evaluation of cultural and non synthetic...
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EVALUATION OF CULTURAL AND NON SYNTHETIC METHODS FOR SOUTHERN CRABGRASS (Digitaria ciliaris) MANAGEMENT IN ST. AUGUSTINEGRASS LAWNS
By
BRIAN GLENN
A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2011
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© 2011 Brian Glenn
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To my wife, Rachel, and my daughter Julia
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ACKNOWLEDGMENTS
I would like to thank my major advisor, Dr. Barry Brecke, for the opportunity and
help he gave me to pursue this degree. I also thank my committee co-chair, Dr. Jason
Ferrell, for all of the help with presentations and getting a handle on everything. Special
thanks to Dr. Bryan Unruh for answering many a random question, and Dr. Greg
MacDonald and Dr. Kevin Kenworthy for advice they gave on my project.
I thank all the grad students at the weed shop for the encouragement and laughs,
especially Neha Rana for the many statistics questions. A special thanks to everyone at
the WFREC, especially Adam White and Vernon Tedder for all the hard work and
keeping everything alive. Above all, I would like to thank my family, my wife Rachel and
my daughter Julia for their love and support, and sticking with it through the summers at
the farm.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS .................................................................................................. 4
LIST OF TABLES ............................................................................................................ 7
LIST OF FIGURES .......................................................................................................... 9
ABSTRACT ................................................................................................................... 10
CHAPTER
1 INTRODUCTION .................................................................................................... 12
Management Strategies .......................................................................................... 14 Current Strategies Using Herbicides ................................................................ 15
Preemergence control ................................................................................ 15 Postemergence control .............................................................................. 15
Alternative Strategies ....................................................................................... 16
Cultural practices ....................................................................................... 16 Alternative herbicides ................................................................................. 19
Summary ................................................................................................................ 20
2 CULTURAL PRACTICES ....................................................................................... 22
Materials and Methods............................................................................................ 23 General Procedures ......................................................................................... 23
Irrigation ..................................................................................................... 24
Mowing height ............................................................................................ 25 Nitrogen fertility .......................................................................................... 25
Evaluation ......................................................................................................... 25 Results and Discussion........................................................................................... 26
Crabgrass Cover and Count - Jay, Florida ....................................................... 26
Crabgrass Cover and Count - Citra, Florida ..................................................... 29 St. Augustinegrass Quality ............................................................................... 30
Summary ................................................................................................................ 31
3 ALTERNATIVE HERBICIDES ................................................................................ 47
Materials and Methods............................................................................................ 48 Alternative Herbicide Greenhouse Evaluation .................................................. 48 Alternative Herbicide Field Evaluation .............................................................. 49 AG Crabgrass Killer Ingredient Greenhouse Evaluation .................................. 50
Results and Discussion........................................................................................... 50 Alternative Herbicide Greenhouse Evaluation .................................................. 50
Crabgrass control ....................................................................................... 50
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Shoot dry weights ...................................................................................... 52
Alternative Herbicide Field Evaluation .............................................................. 53 Crabgrass control ....................................................................................... 53
St. Augustinegrass tolerance ..................................................................... 55 AG Crabgrass Killer Ingredient Evaluation ....................................................... 56
Summary ................................................................................................................ 58
APPENDIX: FIGURES AND TABLES FROM REMOTE SENSING DATA .................... 77
LIST OF REFERENCES ............................................................................................... 79
BIOGRAPHICAL SKETCH ............................................................................................ 83
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LIST OF TABLES
Table page 2-1 Influence of irrigation and fertility on crabgrass cover in St. Augustinegrass in
2009 at Jay, FL. .................................................................................................. 35
2-2 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass in 2009 at Jay, FL. .................................................................... 36
2-3 Influence of irrigation and fertility on crabgrass cover in St. Augustinegrass in 2010 at Jay, FL. .................................................................................................. 37
2-4 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass in 2010 at Jay, FL. .................................................................... 38
2-5 Influence of mowing height on crabgrass cover in St. Augustinegrass in 2009 at Jay, FL. ........................................................................................................... 39
2-6 Influence of mowing height on crabgrass grid count in St. Augustinegrass in 2009 at Jay, FL. .................................................................................................. 39
2-7 Influence of mowing height on crabgrass cover in St. Augustinegrass in 2010 at Jay, FL ............................................................................................................ 40
2-8 Influence of mowing height on crabgrass grid count in St. Augustinegrass in 2010 at Jay, FL ................................................................................................... 40
2-9 Influence of fertility on crabgrass cover in St. Augustinegrass in 2009 at Citra, FL .............................................................................................................. 41
2-10 Influence of fertility on crabgrass cover in St. Augustinegrass in 2010 at Citra, FL ....................................................................................................................... 41
2-11 Influence of fertility on crabgrass grid count in St. Augustinegrass in 2009 at Citra, FL .............................................................................................................. 41
2-12 Influence of fertility on crabgrass grid count in St. Augustinegrass in 2010 at Citra, FL .............................................................................................................. 41
2-13 Response of St. Augustinegrass to fertility in 2009 in Jay, FL. ........................... 42
2-14 Response of St. Augustinegrass to fertility in 2010 in Jay, FL. ........................... 42
2-15 Response of St. Augustinegrass to fertility in 2009 in Citra, FL. ......................... 42
2-16 Response of St. Augustinegrass to fertility in 2010 in Citra, FL. ......................... 43
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3-1 Alternative herbicide treatments for greenhouse evaluation ............................... 60
3-2 Alternative herbicide treatments for field evaluation. .......................................... 61
3-3 Treatments for AG Crabgrass Killer ingredient evaluation. ................................. 61
3-4 Crabgrass control with alternative herbicides in the greenhouse 7 days after application - Trial I ............................................................................................. 62
3-5 Crabgrass control with alternative herbicides in the greenhouse 7 days after application - Trial II ............................................................................................. 63
3-6 Crabgrass control with alternative herbicides in the greenhouse 21 days after application - Trial I .............................................................................................. 64
3-7 Crabgrass control with alternative herbicides in the greenhouse 21 days after application - Trial II ............................................................................................. 65
3-8 Crabgrass shoot dry weights - Trial I .................................................................. 66
3-9 Crabgrass shoot dry weights - Trial II ................................................................. 67
3-10 Crabgrass control in the field with alternative herbicides 7 days after application - 2009 .............................................................................................. 68
3-11 Crabgrass control in the field with alternative herbicides 7 days after application - 2010 ............................................................................................... 69
3-12 Crabgrass control in the field with alternative herbicides 21 days after application - 2009. .............................................................................................. 70
3-13 Crabgrass control in the field with alternative herbicides 21 days after application - 2010 .............................................................................................. 71
3-14 St. Augustinegrass injury from alternative herbicides 7 days after application - 2009 ................................................................................................................. 72
3-15 St. Augustinegrass injury from alternative herbicides 7 days after application - 2010 ................................................................................................................. 73
3-16 St. Augustinegrass injury from alternative herbicides 21 days after application - 2009 ................................................................................................................. 74
3-17 St. Augustinegrass injury from alternative herbicides 21 days after application - 2010 ................................................................................................................. 75
3-18 Postemergence crabgrass control with Crabgrass Killer ingredients 14 days after application. ................................................................................................. 76
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3-19 Shoot dry weights as influenced by AG Crabgrass Killer ingredients. ................ 76
LIST OF FIGURES
Figure page 2-1 Influence of irrigation and fertility on crabgrass grid count in St.
Augustinegrass with no irrigation in 2009 in Jay, FL. .......................................... 44
2-2 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with ET irrigation in 2009 in Jay, FL. ......................................... 44
2-3 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with daily irrigation in 2009 in Jay, FL. ...................................... 44
2-4 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with no irrigation in 2010 in Jay, FL. .......................................... 45
2-5 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with ET irrigation in 2010 in Jay, FL. ......................................... 45
2-6 Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with daily irrigation in 2010 in Jay, FL. ...................................... 45
2-7 Total rainfall by month in 2009 and 2010 in Jay, FL. .......................................... 46
2-8 Total rainfall by month in 2009 and 2010 in Citra, FL. ........................................ 46
4-1 Percent volumetric water content based on irrigation and nitrogen fertility in Jay, FL on July 21, 2010. ................................................................................... 77
4-2 Chlorophyll count based on mowing height and nitrogen fertility in Jay, FL on July 22, 2009. ..................................................................................................... 77
4-3 Chlorophyll count based on mowing height and nitrogen fertility in Jay, FL on July 21, 2010. ..................................................................................................... 78
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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science
EVALUATION OF CULTURAL AND NON SYNTHETIC METHODS FOR SOUTHERN CRABGRASS (Digitaria ciliaris) MANAGEMENT IN ST. AUGUSTINEGRASS LAWNS
By
Brian Glenn
May 2011 Chair: Barry Brecke Cochair: Jason Ferrell Major: Agronomy
Southern crabgrass (Digitaria ciliaris (Retz.) Koeler) is a common weed problem
in turfgrass throughout the United States, particularly in St. Augustinegrass
(Stenotaphrum secundatum [Walt.] Kuntze) lawns in Florida. Due to recent herbicide
label changes, and lack of tolerance, no postemergence herbicides are currently
available to the homeowner for crabgrass control in St. Augustinegrass (Gale, 2003).
Alternative weed control methods such as cultural practices and alternative herbicides
have been investigated to a limited extent by others for postemergence crabgrass
management (Busey and Johnston, 2006). Experiments were conducted at the West
Florida Research and Education Center in Jay, Florida and at the Plant Science
Research and Education Unit in Citra, Florida to more extensively evaluate cultural
practices for crabgrass management. Three irrigation treatments (no irrigation,
irrigation based on evapotranspiration (ET), and daily irrigation), three mowing heights
(5, 7.5, 10 cm), and four fertility treatments (0, 98, 146, 195 kg N ha-1) split into three
applications throughout the year (April, June, August) were used. Crabgrass counts
were significantly higher in plots that received irrigation daily, compared to ET and non-
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irrigated blocks. Crabgrass density increased as mowing height decreased at Jay, FL.
Plots that were not fertilized had the lowest crabgrass counts, while those receiving
fertility showed increased counts, usually increasing with increasing nitrogen rate.
Treatments that followed IFAS recommendations for irrigation, mowing height, and
fertility in St. Augustinegrass had crabgrass counts 77% less than treatments that did
not follow recommendations in August of 2010. Alternative herbicides (defined as non-
synthetic chemicals that have herbicidal properties) evaluated included acetic acid
(vinegar), borax, sodium bicarbonate (baking soda), and Garden Weasel AG Crabgrass
Killer (an improved sodium bicarbonate formulation including cinnamon, flour, and
cumin). Greenhouse and field trials were conducted at Jay, FL to test product efficacy
in controlling crabgrass and turf injury. In the greenhouse, one rate of vinegar (2x 280.6
L ha-1) and two rates of AG Crabgrass Killer (976.6 and 1464.9 kg ha-1) provided ≥ 70%
control for 1-2 leaf crabgrass 7 days after application (DAA). By 21 DAA, only asulam
(a synthetic herbicide included for comparison) provided ≥ 70% control at any weed
stage. No alternative herbicide provided ≥ 70% control weed control at any weed stage
longer than 7 DAA. Initial turf injury was very high for most rates of vinegar, sodium
bicarbonate, and AG Crabgrass Killer, causing ≥ 20% St. Augustinegrass damage 7
DAA. By 21 DAA, turf injury levels had fallen to ≤ 20% for all treatments except higher
rates of sodium bicarbonate and AG Crabgrass Killer. Although acceptable levels of
control were not consistently seen from any alternative herbicide tested, they may have
a future role as a supplement to proper cultural practices for crabgrass suppression in
St. Augustinegrass.
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CHAPTER 1
INTRODUCTION
Southern crabgrass (Digitaria ciliaris (Retz.) Koeler) is a summer annual grass
species that is native to the Old World and it infests many tropical and subtropical areas
of the world (Clayton et al. 2006). In the United States, its range is northward along the
coastal plains into Connecticut, east of the Appalachians, throughout Florida, extending
west into Texas, Nebraska and Kansas (Murphy 2007). Leaf blades measure 3 - 25 cm
in length, and 2-10 mm in width (Anonymous 2008). Southern crabgrass is
characterized by dense hairs on both sides of the leaf and sheath surface. The ligule is
membraneous and toothed. Seed heads are compromised of 2 to 9 racemes that
branch at varying locations. It can be tufted, prostrate or spreading; its stems are
branched and it can root at the nodes (Clayton et al. 2006). Reproducing from seed, it
is very prolific (several seed crops can be produced every year) and seeds are spread
mainly by mechanical means (Peters and Dunn 1971). Southern crabgrass can
germinate under no light conditions, but germination is higher with light (Chauhan and
Johnson 2008). Seeds germinated at a rate of <40% when daytime/nighttime
temperatures were 25/15 C; germination increased to >80% when temperatures were
30/20 C (Chauhan and Johnson 2008). Spreading can also occur by plants rooting at
nodes, often forming dense mats. Southern crabgrass is differentiated from large
crabgrass (Digitaria sanguinalis (L.) Scop) by the length of prickle on the abaxial leaf
surface (Gilani et al, 2002) and the length of the second glume (Clayton et al. 2006). Its
habitat includes open fields, pastures, disturbed areas, and lawns (Holm et al. 1977).
Other common names include Henry’s crabgrass, summer grass, and tropical finger
grass (Murphy 2007).
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St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.) is a warm season
perennial turfgrass that is the most widely used species for lawns in Florida where it is
grown on 1.2 million home lawns across the state (Hodges et al. 1994). Its origins can
be traced to the warm climates of the Old World, but alternative hypotheses state that it
could be native to North America, with samples having been found in the Carolinas in
the late 1700’s (Hanson et al. 1969; Busey 2000). St. Augustinegrass is characterized
by thick leaf blades and large running stolons that can produce heavy thatch requiring
mechanical thatch removal. The recommended mowing height is 7.6 to 10.2 cm in for
‘Floratam’ St. Augustinegrass in Florida, and the generalized mean summer
evapotranspiration rate is 4.3 to 6.6 cm-1 week (Unruh and Elliot 1999). St.
Augustinegrass also requires a higher mowing height than other common warm season
turfgrasses including bermudagrass (Cynodon dactylon (L.) Pers.) (Trenholm et al.
2000; Christians 2004).
St. Augustinegrass has been in use as a turfgrass since 1880, but did not reach its
current popularity until the 1970’s, when Texas A&M and the University of Florida
released the cultivar ‘Floratam’ (Busey 2000). It is usually propagated vegetatively, due
to limited or no seed production. Its range includes Florida and the Gulf Coast states,
extending west into Texas (Busey 2000). Winter kill limits its use to the southern portion
of the transition zone. Colder winters induce dormancy until soil temperatures warm in
the spring to above 16˚C (Christians and Engelke 1994). St. Augustinegrass has
relatively poor cold tolerance, moderate salt tolerance, and is subject to winter
desiccation in drier climates (Christians 2004). It is also susceptible to southern chinch
bugs (Blissus insularis), gray leaf spot (Pyricularia grisea), large patch (Rhizoctonia
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solani) and St. Augustinegrass decline (SAD), caused by the panicum mosaic virus
(PMV). Advantages include moderate to good shade tolerance depending on the
cultivar, rapid growth, and thick canopy that competes well with weeds.
Management Strategies
Southern crabgrass is a troublesome weed that appears and persists in residential
lawns throughout the southeastern United States. Each year in the state of Florida, $90
million dollars are spent on herbicides for weed control in turfgrass (Hodges et al. 1994).
Coupled with the high cost of chemicals, new pesticide regulations and environmental
protection statutes have caused applicators to begin to look for alternative means by
which to control turf pests. Changing public opinion has also led many homeowners to
desire organic weed management programs for their lawns, which is characterized by
using non-chemical methods such as mowing, mulching, and cultivation as well as non-
synthetic herbicides (Ferguson and Chase 2004). The original organic movement
began in Great Britain in the 1940’s, centered on soil conservation and decreased
tillage (Macilwain 2004). In the past ten years the movement has seen resurgence, and
has also included increasing biodiversity, reducing erosion, and reducing materials that
may be moved to off target sites (Macilwain 2004). Current research in organic systems
is mainly directed toward crop production systems, and there is a need for the
evaluation of organic weed control methods for use in turfgrass.
Another reason for interest in alternative weed control products is the lack of
postemergence herbicides labeled for use in St. Augustinegrass turf. Currently, there
are few selective herbicides labeled for residential postemergence control of grassy
weeds in improved St. Augustinegrass cultivars. Preemergence options are still
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available, but they must be applied before weeds germinate in order to have control
activity.
Current Strategies Using Herbicides
Preemergence control
Many herbicide options are available to homeowners with established lawns for
control of crabgrass preemergence. The herbicides in the triazine herbicide family are
photosystem II inhibitors that are used extensively in St. Augustinegrass (Teuton et al.
2004; Senseman 2007). Mitosis inhibitors are also used preemergence and include S-
metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-{(1S)-2-methoxy-1-
methyethyl}acetamide], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-
dinitrobenzenamine], prodiamine [2,4-dinitro-N3, N3-dipropyl-6-(trifluoromethyl)-1,3-
benzenediamine] and napropamide [N,N-diethyl-2-(1-naphthalenyloxy) propanamide]
(Senseman 2007). Oxidiazon [3-{2,4-dichloro-5-(1-methylethoxy)phenyl}-5-(1,1-
dimethylethyl)-1,3,4-oxadiazol-2-(3H)one] is a protoporphyrinogen oxidase inhibitor
which is also used, and often in conjunction with other herbicides to broaden the
spectrum of control (Senseman 2007).
Postemergence control
Currently, there are few selective herbicides labeled for postemergence control of
grassy weeds in improved St. Augustinegrass cultivars in residential settings. Asulam
[methyl {(4-aminophenyl) sulfonyl} carbamate], a dihydropteroate synthetase inhibitor
used for postemergence control of crabgrass in St. Augustinegrass, is no longer labeled
for residential use (Gale 2003). Label changes have made atrazine [6-choro-N-ethyl-N-
(1-methylethyl)-1,3,5-triazine-2,4-diamine] a restricted use pesticide, making it
unavailable to the homeowner without a pesticide applicator license. New restrictions
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include reduced use rates and imposed buffer zones around impounded water.
Ethofumesate [2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] is
relatively tolerant in St. Augustinegrass and has been used for bermudagrass
suppression (Johnson and Carrow 1995). It has shown to have fair control of
crabgrass, and is labeled for residential turf. However, label restrictions require
application by a licensed pesticide applicator.
Alternative Strategies
Cultural practices
Cultural control practices are often used in integrated pest management programs
in conjunction with chemical means as another tool for decreasing weed pressure.
Cultural practices used in turf situations can include mowing height, cultivation practices
(i.e., aerification, verticutting), fertility, and irrigation scheduling. With the right
combination of methods, these practices can provide a means of managing weed
populations with lower inputs and possibly lessen the potential negative impacts of
herbicides such as weed resistance, leaching, and drift.
Mowing height. Mowing is a common practice in most turfgrass situations.
Increasing mowing height is generally accepted to improve turf health. However, many
applications such as putting greens and athletic fields can call for very low heights.
When easily done, an increased mowing height may be a means to decrease the
germination and growth of crabgrass and other weed seeds by limiting the amount of
sunlight that reaches the soil surface. Previous research has provided mixed results
when using mowing height as a means to control crabgrass. Increased mowing heights
reduced crabgrass populations in trials with cool season turf such as Kentucky
bluegrass (Poa pratensis L.) (Dunn et al. 1981), Chewings fescue (Festuca rubra L. ssp.
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fallax (Thuill.) Nyman) (Jagschitz and Ebdon 1985), and tall fescue (Festuca
arundinacea Schreb.) (Dernoeden et al. 1993; Voigt et al. 2001).
Trials with warm-season grasses have been for the most part inconclusive. In
bermudagrass, mowing proved to be inconsistent and did not appear to provide any
weed control of crabgrass (Callahan and Overton 1978). The effect of mowing on weed
growth in St. Augustinegrass was evaluated in south Florida from 2001 to 2003.
Dollarweed (Hydrocotyle umbellate L.) control was not consistently affected by mowing.
Growth of other weeds including Florida pusley (Richardia scabra L.), southern sida
(Sida acuta Burm. f.), and Carolina dichondra (Dichondra carolinensis Michx.) was
reduced in only one year when the weed intensity was the greatest and only at the
highest mowing height (Busey and Johnston 2006). While the results of increased
mowing height in cool season turfgrasses has been documented to decrease crabgrass
populations, the same effects have not been reported in warm season grasses.
Fertility. Depending on the species, turf generally requires a high input of
nitrogen for optimal growth. Nitrogen is usually supplemented by applying fertilizer,
which is available in many different forms. The same nitrogen that is available for the
turf is also available for uptake by weeds. Because of the vigor of most turfgrasses,
plants that receive adequate levels of nitrogen can often out compete weeds for
resources. Using supplemental nitrogen has been shown to reduce weed infestation in
both warm and cool season turfgrasses. Higher nitrogen rates (196 - 300 kg N ha-1 yr-1)
reduced crabgrass populations in tall fescue (Dernoeden et al. 1993; Voigt et al. 2001),
Chewings fescue (Jagschitz and Ebdon 1985), and Kentucky bluegrass (Dunn et al.
1981; Johnson and Bowyer 1982; Murray et al. 1983).
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When fertility level was increased in St. Augustinegrass, weed pressure was
reduced for all weed species evaluated in the study except for dollarweed (Busey and
Johnston 2006). This included a small population of southern crabgrass, but the results
were not definitive because of the size of the sample. The data shows that there is a
strong relationship for higher rates of nitrogen and decreased crabgrass population;
however, more information is needed to better describe the relationship between
nitrogen fertilization and crabgrass growth in warm season grasses such as St.
Augustinegrass.
Irrigation. Based on different water requirements, many turfgrasses need
supplemental irrigation to remain healthy. Weed species that are found in lawns and
other turf applications can grow under various soil moisture levels, which helps them
remain competitive during drought conditions. The results of different irrigation
regiments are varied among weeds growing in warm and cool season turf. Treatments
in cool season turf infested with annual bluegrass (Poa annua L.) showed little or no
change in weed populations by changing the frequency of watering (Jiang et al. 1998).
In perennial ryegrass (Lolium perenne L.), a study showed that irrigation treatments had
no effect on dandelion (Taraxacum officinale) or smooth crabgrass (Digitaria
ischaemum Schreb.) (Jiang et al. 1998). In St. Augustinegrass, dollarweed coverage
increased with increasing irrigation, while density of other weeds including southern
crabgrass decreased (Busey and Johnston 2006). Although the previous study
included crabgrass, the population density may have been too low to detect changes in
level of infestation.
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Alternative herbicides
Alternative herbicides are those which are not the synthetic chemicals traditionally
used to control weeds. These include common household products such as sodium
bicarbonate (baking soda), acetic acid (vinegar), sodium chloride, and borax. Little
information has been published in regards to the use and effectiveness of these
products as an herbicide (Chase et al. 2004). The recent demand for organic food
production and products has contributed to the exploration of natural products for use in
weed management.
Sodium bicarbonate (baking soda) has been shown to be antagonistic when used
with synthetic herbicides (Thelen et al. 1995). When sodium bicarbonate was used
alone as a postemergence herbicide, some activity was noted. A 1994 study conducted
by Dr. Barry Brecke at the University of Florida showed sodium bicarbonate provided
between 35 and 45% control of crabgrass at 28 days after application when applied to
crabgrass at the 1-3 leaf growth stage. Application rates were between 49 and 98 kg ai
ha-1. New products that contain sodium bicarbonate, mixed with other natural materials,
are being marketed to control crabgrass postemergence. Claims include crabgrass
control while being safe for most warm season turfgrasses, including St. Augustinegrass
(Anonymous 2005). Continued research is needed to determine tolerance of St.
Augustinegrass to sodium bicarbonate and effectiveness for crabgrass control.
Acetic acid, which is the principle ingredient in vinegar, has been researched in
the past few years to test its effectiveness in weed management. Organic growers have
expressed interest because it is considered a natural product and can be used
postemergence. Early research showed effective control of common lambsquarter
(Chenopodium alba L.), giant foxtail (Setaria faberi Herrm.), redroot pigweed
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(Amaranthus retroflexus L.) and smooth pigweed (Amaranthus hybridus L.) at
concentrations of acetic acid ranging from 15 to 30 % (Radhakrishnan et al. 2002;
Evans et al. 2009). Vinegar provided above 80% control of crabgrass 1 day after
treatment when applied at the 2 to 3 leaf growth stage, (Evans and Bellinder 2009).
However, timing was critical in the application of vinegar because it acts as a contact
material, and it was most effective on smaller weeds.
Borax has been tested for its weed control properties since at least the 1940’s
(Allgaier 1944). The most predominant use of borax as an herbicide is to control ground
ivy (Glechoma hederacea L.). Results have varied, but have shown moderate to good
postemergence control of ground ivy in field trials (Rossi et al. 1996; Hatterman-Valenti
et al. 1996). Temporary injury to turfgrass was recorded with all treatments. Because
borax is comprised of the micronutrient boron, toxicity problems are a concern with
continued applications. Levels of boron required to create toxic levels are still unclear.
Research is needed to determine the effectiveness of borax for control of crabgrass and
the sensitivity of St. Augustinegrass to borax.
Summary
The lack of postemergence chemical control for crabgrass in St. Augustinegrass
has lead to interest in areas other than synthetic chemical control. Cultural practices
and alternative herbicides may provide a means to manage southern crabgrass
populations. Potential management strategies should be available for use by
homeowners without excessive complications.
Cultural practices have been used in many turfgrasses to promote plant health and
to suppress weed growth. Research is needed to document the effect that these
practices, specifically mowing height, irrigation, and nitrogen fertility levels, will have on
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St. Augustinegrass quality and crabgrass management. Alternative herbicides are used
in applications such as organic crop production as a means of weed control. They
include common household products such as sodium bicarbonate (baking soda),
vinegar, and borax. Research is needed to document the efficacy of crabgrass control
at different weed stages, and to determine St. Augustinegrass tolerance. The
information gathered from the described research will be used to increase current
management options for postemergence crabgrass control, in particular those strategies
that will augment organic weed control strategies.
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CHAPTER 2 CULTURAL PRACTICES
Southern crabgrass (Digitaria ciliaris (Retz.) Koeler) is an annual grass species
that is native to the Old World and infests many tropical and subtropical temperature
regions around the world (Clayton et al. 2006). The range of adaptation of southern
crabgrass in the United States extends from Texas, across to Florida, and northeast of
the Appalachians to Connecticut (Murphy 2007). It infests most open areas including
pastures, fields, lawns, golf courses, athletic fields and commercial turf (Holm et al.
1977).
Southern crabgrass poses a particular challenge to homeowners, due to the
limited control options available in St. Augustinegrass (Stenotaphrum secundatum
[Walt.] Kuntze). Sensitivity to many herbicides, along with label changes to herbicides
once used in St. Augustinegrass, have resulted in a situation with no available
postemergence herbicides for southern crabgrass control in St. Augustinegrass lawns.
This has required researchers to exploring options other than traditional synthetic
chemicals for crabgrass management.
Cultural practices are used by turfgrass managers and homeowners as a way to
maintain and improve plant health. These practices include mowing height, irrigation,
aerification, vertical mowing, and fertilization. Many of these practices have been
researched in the past to determine their impact on weed populations. Weed pressure
was decreased in St. Augustinegrass at a mowing height of 11.4 cm, but not
significantly at any other height evaluated (6.4 and 8.9 cm) (Busey and Johnston 2006).
Dollarweed coverage increased in St. Augustinegrass with an increase in irrigation,
while density of other weeds including crabgrass decreased (Busey and Johnston
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2006). When fertility level was increased, weed pressure was reduced for all weed
species evaluated in the study except for dollarweed (Busey and Johnston 2006).
However, little research has concentrated on the effect of cultural practices on
managing crabgrass in St. Augustinegrass.
Because of the extensive amount of St. Augustinegrass grown for home lawns in
the state of Florida (Hodges et al. 1994) research is needed to evaluate of crabgrass
management using cultural practices. This information can also be used to create
BMPs (Best Management Practices) for homeowners with St. Augustinegrass lawns
and crabgrass populations. Therefore the objective of this research was to determine
the effect of mowing height, irrigation, and nitrogen fertility on management of crabgrass
populations and St. Augustinegrass performance.
Materials and Methods
General Procedures
Studies to evaluate the effects of cultural practices for southern crabgrass
management were conducted in two locations across north Florida. The first was
established at the West Florida Research and Education Center in Jay, Florida.
‘Classic’ St. Augustinegrass was sodded during the second week of April of 2009. Nine
blocks measuring 9.1 m by 9.1 m were sodded, separated by 3.0 m alleys. Treatments
were arranged as a split-split plot design with three replications. Main plots were
irrigation, sub-plots were mowing height and sub-sub-plots were fertility treatments. Soil
at the Jay, FL location was a Dothan fine sandy loam (fine-loamy, siliceous, thermic
Plinthic Paleudults) with 77% sand, 14% silt, 9% clay, and 2% organic matter.
The second location was the Plant Science Research and Education Unit in
Citra, Florida. The study site at the Citra, FL location was a preexisting block of
24
‘Floratam’ St. Augustinegrass. Treatments were arranged in a split plot design with
three replications. Main plots were mowing height and sub-plots were fertility
treatments. Irrigation was not used as a treatment due to limitations in installing
irrigation at the site. Plot size at both locations was 3 m by 1.5 m. Soil characteristics
at the Citra, FL location is a Hague series sand (loamy,siliceous, semiactive,
hyperthermic Arenic Hapludalfs), with a cation exchange capacity of 6.1, 1.4% organic
matter, and pH 5.8. Southern crabgrass was overseeded on May 15 and June 13 in
2009 and on March 15 and 19 in 2010 at Jay, FL and Citra, FL, respectively. ‘Red
River’ southern crabgrass seed obtained from Elstel Farm and Seeds1 was overseeded
both years at a rate of 98 kg ha-1 applied with a drop spreader.
Irrigation
Irrigation pipes and sprinklers were installed during April of 2009. An irrigation
audit was performed in June of 2009 to ensure irrigation uniformity, distribution, and rate
of delivery. Irrigation treatments were separated into three frequency regiments: 1) no
supplemental irrigation, 2) water replacement based on evapotranspiration (ET) rates
for St. Augustinegrass, and 3) irrigation applied daily. The evapotranspiration rate used
was that calculated as described by Unruh and Elliot, (1999). The crop coefficient value
of St. Augustinegrass (0.8) was multiplied by the ET rate added for the previous seven
days. The value was then divided by two, and the amount was applied to plots through
irrigation. Water need based on the recommended ET was applied twice weekly..
Irrigation treatments began as St. Augustinegrass greened up in the spring and
continued until the onset of dormancy in the fall.
1 Elstel Farm and Seeds, 2640 Springdale Road, Ardmore, OK 73401-9106
25
Mowing height
Mowing height treatments were the split-plots at Jay, FL and the main plots at
Citra, FL. Three different mowing heights were used: 5, 7.5, and 10 cm. The 7.5 and
10 cm heights represent the recommended mowing heights for St. Augustinegrass in
Florida while the 5 cm is lower than recommended (Unruh and Elliot 1999). Plots were
mowed using a walk-behind mulching rotary mower. Clipping were not collected. Plots
were mowed weekly from the time of St. Augustinegrass green up to fall dormancy
Nitrogen fertility
Nitrogen was applied at 0, 98, 146, and 195 kg N ha-1 yr-1, simulating low to high
recommendations of fertilization for St. Augustinegrass by UF/IFAS (Unruh and Elliot
2009). The four rates of nitrogen fertilizer were divided into three sequential
applications applied in April, June, and August. A granular fertilizer (18-0-18) with 35%
slow release nitrogen was used and was applied to plots using a shaker can.
Evaluation
Plots were evaluated with grid counts and visual ratings of crabgrass populations
every 2 weeks after the first fertilizer application. Crabgrass density was estimated
using a 0.9 m2 grid that is divided into 36 squares measuring 13 cm2 each. The grid
was placed in the plot to be evaluated and the number of squares containing crabgrass
was recorded. In addition crabgrass percent cover was visually estimated using a scale
of 0-100%, 0 indicating no crabgrass present and 100 equal to complete crabgrass
cover of the plot.
Turf quality was visually estimated using a scale of 1-9 in accordance to standard
evaluation procedures set by the National Turfgrass Evaluation Program (NTEP)
26
According to NTEP,1 is the poorest quality (dead turf) and 9 is the highest quality
possible (NTEP 2010). An acceptable turf quality rating was 6 or higher.
Data were subject to an analysis of variance using the PROC GLIMMIX of SAS
(2008) to determine possible interactions and treatment effects. Means were separated
using Tukey’s HSD test. Weed counts and weed cover data were transformed using a
square root transformation due to non-normal distribution.
Results and Discussion
Crabgrass Cover and Count - Jay, Florida
Treatment by year and treatment by evaluation date interactions at the Jay, FL
location were detected for all observations. Therefore, data have been presented
separately by year for crabgrass count, cover, and St. Augustinegrass quality. An
interaction was observed between irrigation and nitrogen fertility both years. In 2009,
crabgrass cover was significantly higher in plots with no supplemental irrigation with
higher rates of nitrogen, particularly early in the season (Table 2-1). However, in
irrigated plots, crabgrass density did not differ among nitrogen treatments later in the
season regardless of whether plots were irrigated based on ET or irrigated daily.
In 2009 crabgrass counts showed results similar to those observed with crabgrass
cover (Table 2-1 vs. Table 2-2). Only treatments with no supplemental irrigation had
crabgrass counts >10 throughout the year and counts increased with increasing fertility
only in the plots that did not receive supplemental irrigation (Figure 2-1). Nitrogen level
had no effect on crabgrass counts whether irrigated based on ET or on a daily schedule
(Figure 2-2 and 2-3).
In 2010, treatments that were irrigated daily had the most crabgrass cover
consistently throughout the year after June with > 35% cover for plots receiving nitrogen
27
(Table 2-3). Treatments with no irrigation and ET irrigation did not have crabgrass
cover exceeding 30% (Table 2-3) nor crabgrass count >16 (Table 2-4) at any date. All
daily irrigation treatments receiving nitrogen had significantly higher crabgrass cover
than any ET irrigated treatment in June (Figure 2-4, 2-5, and 2-6). All daily irrigated
plots that were also fertilized at any level had higher crabgrass counts than any other
treatment (Table 2-4). All treatments that did not receive nitrogen had low crabgrass
cover and had low crabgrass counts.
The results from nitrogen treatments in this study are not in agreement with
previous research using nitrogen fertility for weed management. Busey and Johnston
(2006) found that as nitrogen levels increased in St. Augustinegrass, crabgrass
populations decreased. The difference in results could be attributed to the small
population size (compared with 21 other weeds in plots) of crabgrass in the Busey and
Johnston study. The results in our study showed that the lowest crabgrass densities
were obtained in the absence of supplemental nitrogen to St. Augustinegrass. This
level of input might not be desirable due to the likelihood of reduced turf quality. If
nitrogen is used, the amount should be determined based on various site conditions,
including availability of irrigation and history of crabgrass infestation.
Results from irrigation treatments in 2009 were similar to findings of Busey and
Johnston study (2006) where crabgrass coverage decreased with increasing irrigation.
In 2010, results were different as crabgrass population was significantly higher at the
highest rate of irrigation. If St. Augustinegrass is newly sodded, it should remain
irrigated until established to prevent rapid decline resulting in open areas that could lead
to crabgrass encroachment. When St. Augustinegrass is well established, irrigation
28
should be applied sparingly to maintain turf health. When applied in excess of ET
replacement crabgrass growth is encouraged. If turf does not receive any supplemental
irrigation, nitrogen levels should be limited to minimize crabgrass growth due to excess
nutrients.
There were no interactions between treatments and mowing height; therefore,
data were pooled. In 2009, crabgrass cover was not significantly different at any date
(Table 2-5). Crabgrass counts increased significantly as mowing height was increased
on two dates in September (Table 2-6). A few rating dates showed that St.
Augustinegrass mowed at 10.2 cm had the most crabgrass cover and counts
throughout much of the year. In 2010, crabgrass cover and counts increased as mowing
height decreased on most dates (Table 2-7 and Table 2-8). Crabgrass counts were the
greatest at the lowest mowing height for each evaluation date. Counts were significantly
lower in plots mowed at 10 cm than 5 cm for four dates during the year (Table 2-8).
Crabgrass cover appeared to be higher at the lowest mowing height for every date
except August 18.
The inconsistent results over years observed in this study is similar to previous
research describing the effect of mowing height on crabgrass coverage in St.
Augustinegrass. Busey and Johnston (2006) observed a significant reduction in
crabgrass coverage in only one year of a 3 year study at the highest mowing height
(6.4, 8.9, and 11.4 cm). Results in this study differed between years, and the highest
mowing height was only effective in decreasing crabgrass cover in 2010.
The differences in mowing height on crabgrass cover between years at the Jay, FL
location could be attributed to both differences in stage of turfgrass establishment and
29
date of overseeding of crabgrass. St. Augustinegrass sod was laid on April 17, 2009.
The sod was watered regularly to promote establishment until irrigation treatments
began on June 13. The length of establishment before irrigation treatments were
applied could have had an effect on crabgrass cover, as higher temperatures and lower
levels of rainfall are typical in June in north Florida. Treatments that did not receive
irrigation showed higher crabgrass cover than irrigated plots. Lack of irrigation usually
adds stress to turfgrass, causing leaf firing and eventual thinning of the turf canopy.
Weeds can take advantage of open areas in the canopy, leading to increased
populations. Crabgrass was also overseeded in June, well beyond the usual date of
crabgrass emergence. Because southern crabgrass is a summer annual, and usually
begins to emerge as temperatures increase in the spring (Clayton et al. 2006). Average
temperatures in Florida during June are well above levels needed for crabgrass
germination, and are around those needed for optimum growth. Also, fertility treatments
were applied within two weeks of crabgrass overseeding. As the crabgrass began to
emerge, nitrogen was supplied earlier than what would be applied normally. Nitrogen is
first applied in the spring after St. Augustinegrass has almost completely broken
dormancy. Usually this occurs at least one month after crabgrass has begun to
germinate. The addition of nitrogen soon after overseeding could have affected
crabgrass populations in a way that would not be observed if normal management
practices were followed.
Crabgrass Cover and Count - Citra, Florida
There was an interaction between years at the Citra, FL location; therefore, years
are shown separately. Data were pooled by fertility. Mowing height for most dates was
not significant but nitrogen was significant for all dates. Crabgrass cover and counts
30
were the lowest for plots with no nitrogen for each date and highest for plots receiving
195 kg N ha-1 in 2009 and 2010 (Table 2-9; 2-10; 2-11; 2-12).
The impact of nitrogen on crabgrass abundance in Citra, FL did not agree with the
Busey and Johnston (2006), who observed that crabgrass populations decreased as
nitrogen levels increased in St. Augustinegrass. The difference in results could be
attributed to the small amount of crabgrass in the observed population of the earlier
study. The current experiment had crabgrass densities ranging from 2-35% cover,
while Busey and Johnston (2006) reported < 30% cover for all treatments. The data at
the Citra, FL location were similar with the Jay, FL location in that crabgrass populations
were lowest on those plots receiving no supplemental nitrogen. However, crabgrass
populations on plots that were fertilized varied between Jay, FL and Citra, FL. Irrigation
was not a treatment factor at the Citra, FL location, but an interaction was seen between
irrigation and nitrogen at the Jay, FL location. Plots at the Citra, FL location were
irrigated, but did not follow any irrigation regime implemented in Jay, FL. The amount of
rainfall and temperatures also varied between locations (Figure 2-3 and 2-4). The
difference in irrigation frequency, amount, and weather conditions may explain the
difference between crabgrass populations at Citra, FL and Jay, FL.
St. Augustinegrass Quality
There were treatment by year and treatment by date of evaluation interactions for
all irrigation, mowing, and fertility treatments at both locations; therefore, data are
shown separately by year and location. There were no interactions between treatment
factors (irrigation, mowing and fertility); therefore, data were pooled by nitrogen
treatments, being the only significant factor. For all quality ratings, the highest quality
31
was achieved when fertilized at 195 kg N ha-1, and the lowest quality at 0 kg N ha-1
(Table 2-13; 2-14; 2-15; 2-16).
In Jay and Citra, FL, no untreated plot achieved an acceptable quality rating
(Table 2-13 and Table 2-14) on any rating date in 2009 and 2010. Treatments fertilized
at 98 kg N ha-1 and 146 kg N ha-1 achieved acceptable quality ratings, but not for the
entire season. However, St. Augustine quality was >6 for treatments fertilized at 195 kg
N ha-1 for all evaluation dates except early season in June 2010 at Citra, at both
locations, in 2009 and 2010.
Differences between years could be attributed to various environmental factors.
In both locations, 2010 had significantly longer periods throughout the summer without
rainfall. Because plots that are not irrigated only receive water from rainfall, these
periods could have possibly led to water stress beyond the permanent wilting point.
Even if rainfall was plentiful after an extended dry period, turf decline would have been
irreversible. Also, since plot layout was unchanged between years, St. Augustinegrass
plots not receiving nitrogen had more time elapse from the last application of nitrogen
(applied at the sod farm before sod was harvested). The extended absence of
supplemental nitrogen may have caused further decline of quality in 2010 from ratings
taken in the similar time of year in 2009.
Summary
Cultural practices are used in turfgrass management to improve plant health but
the impact on weed management has not been exhaustively explored. These practices
can include altering mowing height, irrigation, and nitrogen fertility. Due to the lack of
postemergence options available to homeowners for southern crabgrass control in St.
Augustinegrass, alternative management techniques were evaluated for effectiveness.
32
Mowing height and nitrogen fertility rate were jointly tested in two locations for two
years; irrigation frequency was tested only at the Jay, FL location for two years.
Crabgrass density and St. Augustinegrass quality responded to mowing, irrigation, and
fertility at the Jay, FL location. At Citra, only fertility impacted crabgrass density and turf
quality.
Effect of irrigation frequency on crabgrass populations was not consistent over
years. In 2009, plots with no irrigation had the highest crabgrass densities. In 2010,
irrigation frequency was positively correlated with crabgrass density. The differences
between years may have resulted from recently sodded St. Augustinegrass and its
establishment in 2009. As irrigation treatments were imposed June 2009, the no
irrigation plots to rapidly decline. This was due to the short period that the turf had to
establish as well as the hot and dry conditions when irrigation treatments were
implemented. The decline led to increased open areas in non irrigated plots, which led
to rapid crabgrass encroachment. Plots irrigated based on ET tended to have the least
increase in crabgrass populations early in the growing season, and lower populations
throughout the summer, due to improved turf health.
Nitrogen fertility was a significant factor for differences in crabgrass populations
for both locations. As nitrogen fertility levels increased, crabgrass populations also
increased for most treatments. The effect of fertility was more pronounced at the Citra,
FL location for both years. Southern crabgrass appears to be competitive with St.
Augustinegrass for nitrogen uptake (Chauhan and Johnson 2008). In making
management recommendations, nitrogen should be limited if crabgrass management is
desired.
33
Mowing height was significant across all dates at Jay, FL, but not at Citra, FL.
Results differed in Jay, FL for 2009 and 2010. The lowest mowing height resulted in the
lowest crabgrass populations in 2009, but the highest levels of crabgrass infestation in
2010. These differences were seen throughout the summer in both years. Possible
explanations for this difference could be the result of late crabgrass planting and turf
establishment in 2009. Newly sodded turf is more susceptible to decline because of
lack of irrigation due to a root system that is still establishing. As a result, those plots
that were not irrigated when turf was still establishing suffered a rapid decline, leading to
open areas in which weeds could establish. Planting crabgrass later in the season can
expose seedlings to optimal growth conditions immediately. This could cause
differences in results seen because crabgrass does not follow the normal summer
annual life cycle that it is exposed to under normal field conditions.
Another factor to be considered is the visual rating process because of the
difficulty of rating crabgrass in frequently mowed St. Augustinegrass turf. Crabgrass
populations at the lower mowing heights may have been underestimated because of
their small size. Another year of data collection would be required accurately assess
the effect of mowing height on managing crabgrass coverage.
Turfgrass quality was significantly affected only by fertility in both locations.
Quality increased for all treatments in correlation to the amount of nitrogen applied to
the turf. In general, the absence of nitrogen did not provide acceptable turf quality,
especially in 2010. Nitrogen applied at the highest level did provide the highest level of
quality, but also encouraged the highest level of crabgrass populations. Nitrogen fertility
34
should be managed based on the level of expected quality with the knowledge that as
quality increases, so does crabgrass incidence.
Based on the results, no single management technique appears to be
responsible for acceptable management of crabgrass. Turfgrass health should be
considered first. Higher mowing heights and a moderate level of both irrigation and
fertility are recommended as Best Management Principles (BMPs) for homeowners to
follow. Those cultural factors evaluated in these studies that resulted in the best
management of crabgrass also seemed to agree with these commonly followed BMPs.
35
Table 2-1. Influence of irrigation and fertility on crabgrass cover in St. Augustinegrass in 2009 at Jay, FL.
Treatment % Crabgrass Cover - Visual
Irrigation Fertility (kg ha-1) 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep
No Irrigation 0 3.3 a-c 10.0 b-d 7.0 abd 24.4 ab 19.4 ab 20.6 ab
98 4.4 a-c 16.9 a-c 13.8 a-c 32.2 ab 27.2 ab 23.3 ab
146 11.4 ab 26.6 ab 18.0 ab 37.2 ab 27.4 ab 28.3 ab
195 12.9 a 35.8 a 20.3 a 43.3 a 32.4 a 35.6 a
ET Irrigation 0 0 c 0 d 3.3 dc 6.6 b 9.1 b 8.3 b
98 0 c 0.8 dc 2.1 dc 6.9 b 9.4 b 10.0 b
146 0 c 0.4 dc 3.2 dc 7.7 b 11.7 ab 12.2 ab
195 0.2 c 0.4 dc 3.7 dc 6.3 b 9.4 b 8.3 b
Daily Irrigation 0 0.2 c 0 d 5.0 b-d 5.8 b 7.3 b 8.3 b
98 0.8 c 6.3 dc 7.6 a-d 11.3 ab 9.4 b 11.7 ab
146 0.4 c 4.1 dc 3.8 cd 6.6 b 7.8 b 9.7 b
195 1.4 bc 8.3 dc 6.4 a-d 6.9 b 13.3 ab 9.4 b
36
Table 2-2. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass in 2009 at Jay, FL.
Treatment Crabgrass Grid Counta
Irrigation Fertility (kg ha-1) 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep
No Irrigation 0 0.7 b 3.0 bc 5.3 a-d 8.3 abc 5.7 abc 7.6 ab
98 2.8 ab 6.2 abc 7.3 abc 10.7 ab 8.8 ab 9.4 ab
146 3.8 ab 9.9 ab 13.9 a 10.6 ab 8.7 ab 10.6 a
195 4.7 ab 15.2 a 13.0 ab 13.2 a 12.1 a 11.3 a
ET Irrigation 0 0 b 0 c 0.8 d 4.9 abc 2.0 bc 3.4 ab
98 0 b 0.2 c 0.7 d 3.7 bc 2.7 bc 3.4 ab
146 0 b 0.6 c 0.7 d 4.2 bc 3.0 bc 4.4 ab
195 0 b 0.3 c 1.7 cd 3.8 abc 2.3 bc 2.8 b
Daily Irrigation 0 0.1 b 0 c 3.3 cd 2.4 c 1.4 c 5.6 ab
98 0.6 b 1.8 bc 5.3 a-d 3.2 bc 2.6 bc 4.8 ab
146 0 b 1.6 bc 3.8 bcd 3.2 bc 2.1 bc 4.1 ab
195 0.3 b 3.1 bc 4.8 a-d 3.4 bc 3.7 bc 3.9 ab aCrabgrass presence measured with 36 square grid
37
Table 2-3. Influence of irrigation and fertility on crabgrass cover in St. Augustinegrass in 2010 at Jay, FL.
Treatment % Crabgrass Cover - Visual
Irrigation Fertility (kg ha-1
) 26-May 8-Jun 23-Jun 7-Jul 21-Jul 3-Aug 18-Aug 3-Sep
No Irrigation 0 1.1 c 1.1 d 5.6 c 2.8 de 5.6 d 3.3 ef 7.2 def 12.2 cd
98 6.1 bc 12.2 bcd 16.1 bc 23.3 bc 18.9 c 23.3 bcd 31.1 bc 26.3 abc
146 7.8 abc 12.2 bcd 14.4 bc 28.9 abc 16.1 c 19.4 bcd 22.2 cd 21.7 bcd
195 3.9 bc 19.4 bcd 16.1 bc 25.6 abc 17.8 c 11.1 def 26.7 bc 16.7 cd
ET Irrigation 0 2.8 bc 1.1 d 1.7 c 5.6 de 3.9 d 2.4 f 6.1 ef 5.0 d
98 2.2 bc 1.7 cd 0.6 c 18.3 cd 20.6 c 16.7 b-e 15.0 c-f 15.6 bcd
146 1.7 bc 2.2 cd 2.2 c 27.8 abc 22.2 bc 16.1 b-e 17.8 cde 12.8 cd
195 1.1 c 3.3 cd 1.1 c 15.6 cde 20.0 c 14.4 c-f 15.0 c-f 12.4 cd
Daily Irrigation 0 5.0 bc 0 d 3.9 c 1.1 e 0.6 d 3.9 ef 2.2 f 6.7 cd
98 16.1 ab 25.0 ab 30.6 ab 50.6 ab 49.4 ab 41.1 abc 46.7 abc 45.0 ab
146 25.0 a 30.6 ab 29.4 ab 58.9 a 62.2 a 41.7 ab 58.9 ab 52.2 a
195 25.6 a 54.4 a 56.7 a 58.9 a 73.9 a 62.2 a 70.0 a 50.6 a
38
Table 2-4. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass in 2010 at Jay, FL.
Treatment Crabgrass Grid Counta
Irrigation Fertility (kg ha-1
) 26-May 8-Jun 23-Jun 7-Jul 21-Jul 3-Aug 18-Aug 3-Sep
No Irrigation 0 1.1 c 1.1 d 5.6 c 2.8 de 5.6 d 3.3 ef 7.2 def 12.2 cd
98 6.1 bc 12.2 bcd 16.1 bc 23.3 bc 18.9 c 23.3 bcd 31.1 bc 26.3 abc
146 7.8 abc 12.2 bcd 14.4 bc 28.9 abc 16.1 c 19.4 bcd 22.2 cd 21.7 bcd
195 3.9 bc 19.4 bcd 16.1 bc 25.6 abc 17.8 c 11.1 def 26.7 bc 16.7 cd
ET Irrigation 0 2.8 bc 1.1 d 1.7 c 5.6 de 3.9 d 2.4 f 6.1 ef 5.0 d
98 2.2 bc 1.7 cd 0.6 c 18.3 cd 20.6 c 16.7 b-e 15.0 c-f 15.6 bcd
146 1.7 bc 2.2 cd 2.2 c 27.8 abc 22.2 bc 16.1 b-e 17.8 cde 12.8 cd
195 1.1 c 3.3 cd 1.1 c 15.6 cde 20.0 c 14.4 c-f 15.0 c-f 12.4 cd
Daily Irrigation 0 5.0 bc 0 d 3.9 c 1.1 e 0.6 d 3.9 ef 2.2 f 6.7 cd
98 16.1 ab 25.0 ab 30.6 ab 50.6 ab 49.4 ab 41.1 abc 46.7 abc 45.0 ab
146 25.0 a 30.6 ab 29.4 ab 58.9 a 62.2 a 41.7 ab 58.9 ab 52.2 a
195 25.6 a 54.4 a 56.7 a 58.9 a 73.9 a 62.2 a 70.0 a 50.6 a aCrabgrass presence measured with 36 square grid
39
Table 2-5. Influence of mowing height on crabgrass cover in St. Augustinegrass in 2009 at Jay, FL.
Treatment % Crabgrass Cover - Visual
Mowing Height (cm) 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep
5.1 2.6 a 7.6 a 6.6 a 12.6 a 11.6 a 12.8 a
7.6 3.0 a 10.0 a 8.2 a 16.8 a 16.6 a 15.8 a
10.2 3.2 a 9.8 a 8.7 a 19.3 a 17.8 a 17.8 a
Table 2-6. Influence of mowing height on crabgrass grid count in St. Augustinegrass in 2009 at Jay, FL.
Treatment Crabgrass Grid Counta
Mowing Height (cm) 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep
5.1 1.1 a 3.8 a 4.3 a 4.8 a 3.4 b 4.4 b
7.6 1.4 a 3.4 a 5.1 a 5.7 a 4.5 ab 6.0 ab
10.2 0.7 a 3.3 a 5.8 a 7.4 a 5.9 a 7.4 a aCrabgrass presence measured with 36 square grid
40
Table 2-7. Influence of mowing height on crabgrass cover in St. Augustinegrass in 2010 at Jay, FL
Treatment % Crabgrass Cover - Visual Mowing Height
(cm) 26-May 8-Jun 23-Jun 7-Jul 21-Jul 3-Aug 18-Aug 3-Sep
5.1 12.6 a 21.4 a 17.9 a 38.8 a 30.7 a 23.9 a 25.7 a 25.6 a
7.6 6.1 a 8.9 b 12.6 a 25.0 ab 25.3 a 20.8 a 29.3 a 22.3 a
10.2 5.8 a 10.6 ab 14.0 a 15.6 b 21.8 a 19.2 a 24.7 a 21.4 a
Table 2-8. Influence of mowing height on crabgrass grid count in St. Augustinegrass in 2010 at Jay, FL
Treatment Crabgrass Grid Counta
Mowing Height (cm) 26-May 8-Jun 23-Jun 7-Jul 21-Jul 3-Aug 18-Aug 3-Sep
5.1 4.8 a 6.3 a 2.9 a 19.1 a 17.6 a 11.7 a 14.9 a 14.4 a
7.6 2.3 ab 3.6 a 2.2 a 11.9 ab 13.2 ab 9.4 a 13.5 ab 11.7 a
10.2 1.6 b 3.2 a 2.1 a 7.7 b 9.9 b 8.2 a 9.7 b 10.5 a aCrabgrass presence measured with 36 square grid
41
Table 2-9. Influence of fertility on crabgrass cover in St. Augustinegrass in 2009 at Citra, FL
Treatment % Crabgrass Cover - Visual
Fertility (kg ha-1) 17-Jul 4-Aug 18-Aug
0 1.4 a 2.6 b 2.8 b
98 2.7 a 9.7 ab 12.8 ab
146 1.8 a 28.6 a 27.8 a
195 6.1 a 35.0 a 36.3 a
Table 2-10. Influence of fertility on crabgrass cover in St. Augustinegrass in 2010 at Citra, FL
Treatment % Crabgrass Cover - Visual
Fertility (kg ha-1) 10-Jun 23-Jun 5-Jul 23-Jul 30-Aug
0 0.6 b 1.1 c 5.0 b 0 b 0 b
98 9.4 a 13.3 b 35.0 a 32.2 a 5.6 a
146 16.7 a 23.9 ab 27.2 a 35.6 a 4.1 a
195 27.8 a 38.3 a 44.4 a 47.2 a 12.2 a
Table 2-11. Influence of fertility on crabgrass grid count in St. Augustinegrass in 2009 at Citra, FL
Treatment Crabgrass Grid Counta
Fertility (kg ha-1) 17-Jul 4-Aug 18-Aug
0 0.6 b 1.0 b 1.8 b
98 4.0 ab 5.4 ab 5.7 ab
146 2.4 ab 10.1 a 9.6 a
195 6.1 a 12.6 a 11.1 a acrabgrass presence measured with 36 square Scott’s grid
Table 2-12. Influence of fertility on crabgrass grid count in St. Augustinegrass in 2010 at Citra, FL
Treatment Crabgrass Grid Counta
Fertility (kg ha-1) 10-Jun 23-Jun 5-Jul 23-Jul 30-Aug
0 0.7 b 0.2 c 1.0 b 0 b 0 b
98 4.0 a 4.8 b 14.1 a 14.2 a 3.2 a
146 5.1 a 8.1 ab 21.1 a 15.8 a 3.3 a
195 10.2 a 11.8 a 24.8 a 21.0 a 7.0 a acrabgrass presence measured with 36 square Scott’s grid
42
Table 2-13. Response of St. Augustinegrass to fertility in 2009 in Jay, FL.
Treatment Turfgrass Qualitya
Fertility (kg ha-1) 8-Jul 22-Jul 5-Aug 19-Aug 2-Sep 16-Sep
0 4.9 c 4.9 c 5.8 d 5.9 c 5.9 c 5.9 c
98 5.7 b 5.7 b 6.2 c 6.3 b 6.2 b 6.4 b
146 6.1 ab 6.1 ab 6.4 b 6.5 b 6.4 b 6.4 b
195 6.4 a 6.4 a 6.7 a 6.9 a 6.8 a 6.9 a ameasured using NTEP 1-9 rating scale
Table 2-15. Response of St. Augustinegrass to fertility in 2009 in Citra, FL.
Treatment Turfgrass Qualitya
Fertility (kg ha-1) 17-Jul 4-Aug 18-Aug 12-Sep
0 5.8 c 5.8 c 5.4 c 5.9 b
98 6.7 b 6.6 b 6.1 b 6.5 a
146 6.9 ab 6.7 ab 6.2 b 6.9 a
195 7.3 a 7.1 a 6.6 a 6.9 a ameasured using NTEP 1-9 rating scale
Table 2-14. Response of St. Augustinegrass to fertility in 2010 in Jay, FL.
Treatment Turfgrass Qualitya
Fertility (kg ha-1) 26-May 8-Jun 23-Jun 7-Jul 21-Jul 3-Aug 18-Aug 3-Sep
0 4.6 c 4.0 d 4.1 c 3.8 c 3.9 c 4.2 c 4.1 c 4.2 b
98 5.5 b 5.2 c 5.3 b 6.0 b 5.8 b 6.2 b 6.5 b 7.1 a
146 5.9 ab 5.7 b 5.7 b 6.5 a 6.3 ab 6.6 ab 7.1 a 7.4 a
195 6.2 a 6.3 a 6.3 a 6.8 a 6.8 a 6.8 a 7.3 a 7.1 a ameasured using NTEP 1-9 rating scale
43
Table 2-16. Response of St. Augustinegrass to fertility in 2010 in Citra, FL.
Treatment Turfgrass Quality
Fertility (kg ha-1) 10-Jun 23-Jun 5-Jul 23-Jul 30-Aug
0 3.6 c 3.8 c 3.9 b 3.9 c 4.2 b
98 4.7 b 5.1 b 5.6 a 5.9 b 6.1 a
146 5.2 a 5.8 a 5.7 a 6.5 a 6.3 a
195 5.4 a 6.2 a 6.1 a 6.6 a 6.5 a ameasured using NTEP 1-9 rating scale
44
0 kg N/ha-1
f=-3.1556+4.0762*x-0.3968*x^2 r2 = 0.86
8 kg N/ha-1
f=-1.2111+4.5028*x-0.4623*x^2 r2=0.86
12 kg N/ha-1
f=-0.5778+6.3516*x-0.7976*x^2 r2=0.62
16 kg N/ha-1-1
f=0.4667+7.2198*x-0.9325*x^2 r2=0.62
Date
0 2 4 6
Cra
bg
rass C
ou
nt
(0-3
6)
0
5
10
15
20
25
30
35
0 kg N/ha-1
8 kg N/ha-1
12 kg N/ha-1
16 kg N/ha-1
0 kg N/ha-1
8 kg N/ha-1
12 kg N/ha-1
16 kg N/ha-1
Figure 2-1. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with no irrigation in 2009 in Jay, FL.
0 kg N ha-1
f=-2.1222+1.7115*x-0.1329*x^2 r2 = 0.57
98 kg N ha-1
f=-1.4778+1.1623*x-0.0536*x^2 r2=0.64
146 kg N ha-1
f=-1.3111+1.0571*x-0.0159*x^2 r2=0.66
195 kg N ha-1
f=-2.1444+1.9480*x-0.1885*x^2 r2=0.63
Date
0 2 4 6
Cra
bgra
ss C
ount
(0-3
6)
0
5
10
15
20
25
30
35
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 2-2. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with ET irrigation in 2009 in Jay, FL.
0 kg N ha-1 f=-0.2889+0.4040*x+0.0675*x^2 r2 = 0.61
98 kg N ha-1 f=-1.0778+2.0956*x-0.2123*x^2 r2=0.50
146 kg N ha-1 f=-1.5556+2.0079*x-0.1984*x^2 r2=0.68
195 kg N ha-1 f=-1.7000+2.8369*x-0.3313*x^2 r2=0.61
Date
0 2 4 6
Cra
bgra
ss C
ount
(0-3
6)
0
5
10
15
20
25
30
35
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 2-3. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with daily irrigation in 2009 in Jay, FL.
45
0 kg N ha-1
f=-0.4286=0.7619*x-0.0370*x^2 r2 = 0.64
98 kg N ha-1
f=-5.6944+4.6045*x-0.3638*x^2 r2=0.69
146 kg N ha-1
f=-7.1567+6.3380*x-0.5747*x^2 r2=052
195 kg N ha-1
f=-4.2302+3.4220*x-0.2474*x^2 r2=0.66
Date
0 2 4 6 8
Cra
bgra
ss C
ount
(0-3
6)
0
5
10
15
20
25
30
35
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 2-4. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with no irrigation in 2010 in Jay, FL.
0 kg N ha-1
f=0.7262-0.0503*x+0.0926*x^2 r2 = 0.75
98 kg N ha-1
f=-0.3393+2.3843*x-0.0496*x^2 r2=0.86
146 kg N ha-1
f=-1.7956+3.5589*x-0.2401*x^2 r2=0.53
195 kg N ha-1
f=-0.1230+2.1005*x-0.1164*x^2 r2=0.52
Date
0 2 4 6 8
Cra
bgra
ss C
ount
(0-3
6)
0
5
10
15
20
25
30
35
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 2-5. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with ET irrigation in 2010 in Jay, FL.
0 kg N ha-1
f=2.4345-0.9438*x+0.1435*x^2 r2 = 0.68
98 kg N ha-1
f=-5.3810+8.4220*x-0.6151*x^2 r2=0.70
146 kg N ha-1
f=-3.4603+8.3743*x-0.5807*x^2 r2=0.64
195 kg N ha-1
f=-1.2599+9.2890*x-0.7189*x^2 r2=0.75
Date
0 2 4 6 8
Cra
bgra
ss C
ount
(0-3
6)
0
5
10
15
20
25
30
35
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 2-6. Influence of irrigation and fertility on crabgrass grid count in St. Augustinegrass with daily irrigation in 2010 in Jay, FL.
46
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Rain
fall (
cm
)
0
5
10
15
20
25
30
35
40
45
2009
2010
Figure 2-7. Total rainfall by month in 2009 and 2010 in Jay, FL.
Figure 2-8. Total rainfall by month in 2009 and 2010 in Citra, FL.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Rain
fall (
cm
)
0
5
10
15
20
25
30
35
40
45
2009
2010
47
CHAPTER 3 ALTERNATIVE HERBICIDES
Southern crabgrass (Digitaria ciliaris (Retz.) Koeler) is an annual summer grass
species that is found in many of the tropical and subtropical areas of the world (Clayton
et al. 2006). It is native to the Old World, and can be found throughout the southeast
region of the United States, including Florida (Murphy 2007). Common names include
Henry’s crabgrass, summer grass, and tropical finger grass. It commonly invades
pastures, lawns, roadsides, and open areas (Holm et al. 1977).
St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze) is the most widely
grown turfgrass for lawns in the state of Florida (Hodges et al. 1994). It is characterized
by coarse leaf blades, aggressive growth habit which forms a dense canopy, and thick
stolons (Christians 2004). St. Augustinegrass is also sensitive to many herbicides used
to control crabgrass in other turfgrasses (Unruh 2009). Label changes and restrictions
of herbicides previously used for crabgrass control in St. Augustinegrass have
eliminated postemergence herbicide options for this weed in residential St.
Augustinegrass, leading homeowners to search for new products and methods for
crabgrass management.
Alternative herbicides can be generalized as materials that have been used for
weed control or suppression that are not traditional synthetic chemicals. Many are
products common in households, including sodium bicarbonate, acetic acid (vinegar),
and borax. AG Crabgrass Killer is marketed by Garden Weasel for crabgrass control in
turf contains sodium bicarbonate, cinnamon, cumin, and corn and wheat flour
(Anonymous 2005). The active ingredient for AG Crabgrass Killer is listed as cinnamon,
with inert ingredients making up the remainder of the product. Because of the lack of
48
research on the effectiveness of these products as herbicides, evaluation is needed to
determine which ingredients are causing weed control.
Current research with alternative herbicides is almost completely related to weed
control in organic cropping systems (Chase et al. 2004). The objectives of this research
were to 1) evaluate southern crabgrass control provided by selected alternative
herbicides, 2) measure tolerance of St. Augustinegrass to these products and 3) to
assess the ingredients of AG Crabgrass Killer for effectiveness at controlling southern
crabgrass.
Materials and Methods
Alternative Herbicide Greenhouse Evaluation
Southern crabgrass from Elstel Farm and Seeds1was overseeded at a rate of 98
kg ha-1 on the soil surface in 58-cm2 pots filled with potting media Fafard Mix #42. After
crabgrass emergence, plants were evaluated frequently for stage of growth. Herbicides
treatments were applied at three growth stages; 1-2 leaf, 3-4 leaf, and 1-2 tiller in each
of two trials (Trial I and Trial II). A list of products and use rates is outlined in Table 3-1.
Sodium bicarbonate and AG Crabgrass Killer were applied to crabgrass using a shaker
can. Applications labeled as dry were applied to dry foliage (Table 3-1). Wet
treatments were applied to wet foliage, and lightly misted until all product was
adequately moist. Vinegar, borax, and asulam were applied with a boom sprayer using
a CO2 propellant with 11002 flat fan nozzles calibrated to deliver 187 L ha-1 at 159 kPa.
Vinegar treatments that required a second application were applied 7 days after initial
applications. For Trial II, asulam was added as a comparative control treatment to
1 Elstel Farm and Seeds, 2640 Springdale Road, Ardmore, OK 73401-9106
2 Fafard, Inc. PO Box 790 Agawam, MA 0100-0790 (40% peat, 30% bark, 30% vermiculite v/v).
49
compare crabgrass control between alternative herbicides and a common synthetic
herbicide used in Augustinegrass sod production. Visual estimates of crabgrass control
were recorded at 1, 3, 7, 14, 21, and 28 days after application (DAA). Control was
evaluated using a scale of 0 to 100%, where 0 indicated no crabgrass control and 100
equals crabgrass death.
At the end of each experiment southern crabgrass shoots were harvested and
oven dried at 65˚C for 5 days and shoot dry weights (g) were recorded. All studies were
arranged in a randomized complete block design with four replications and were
conducted twice. Data were analyzed using analysis of variance and means were
separated using a LSD (0.05).
Alternative Herbicide Field Evaluation
Southern crabgrass was overseeded at a rate of 98 kg ha-1 in established
‘Raleigh’ St. Augustinegrass in Jay, Florida in 2009 and 2010. After emergence,
crabgrass plants were evaluated frequently for stage of growth. Treatments were
applied at 1-2 leaf and 1-2 tiller crabgrass growth stage. A list of treatments is outlined
in Table 3-2. Plots measured 1.5 m by 3.0 m and treatments were arranged in a
randomized complete block design with 3 replications and were conducted twice.
Sodium bicarbonate and AG Crabgrass Killer treatments were applied using a
shaker can to plots wet from dew or irrigation event. Vinegar and borax were applied
with a boom sprayer using a CO2 propellant with 11002 flat fan nozzles calibrated to
deliver 187 L ha-1 at 159 kPa. Subsequent vinegar applications were applied 7 days
after initial applications. Turfgrass injury and crabgrass control were visually evaluated
at 1, 3, 7, 14, 21, and 28 DAA. Turfgrass injury ratings were based on a scale of 0 to
100%, 0 indicating no turf injury and 100 equaling completely brown turfgrass.
50
Crabgrass control was evaluated using a scale of 0 to 100%, where 0 indicated no
crabgrass control and 100 equal to complete crabgrass control. Data were analyzed
using analysis of variance and means were separated using an LSD value (0.05).
AG Crabgrass Killer Ingredient Greenhouse Evaluation
Southern crabgrass was seeded at 98 kg ha-1 into 58-cm2 pots containing
Farfald Mix #42. Crabgrass was evaluated after emergence to confirm the correct
growth stage. Treatments were applied to crabgrass at 1-2 leaf and 3-4 leaf stages. A
list of treatments is outlined in Table 3-3. All treatments were applied using a shaker
can. Crabgrass control was visually evaluated at 3, 7, 14, 21, and 28 DAT. Control was
evaluated using a scale of 0 to 100%, where 0 indicated no crabgrass control and 100
equal to complete crabgrass control. At the end of each experiment crabgrass shoots
were harvested and oven dried at 65˚C for 5 days and shoot dry weights (g) were
recorded. All studies were arranged in a randomized complete block design with four
replications. Data was analyzed using analysis of variance and means were separated
with LSD (0.05).
Results and Discussion
Alternative Herbicide Greenhouse Evaluation
Crabgrass control
There was an interaction between trials and growth stages for the greenhouse
experiments; therefore data were analyzed separately for both trials and all stages of
growth. The data presented are the 7 and 21 DAA ratings. These data were selected
to represent control after the product had a short period of time to interact with
crabgrass (7 DAA) and control after a longer interval to determine if regrowth would
occur (21 DAA).
51
Alternative herbicides provided an acceptable level of southern crabgrass control
(70%) only when applied to crabgrass at the 1-2 leaf stage and evaluated 7 DAA for
both trials (Tables 3-4 and 3-5). Control of southern crabgrass 7 DAA was ≥ 70% in
both trials with two applications of 300 grain vinegar at 281 L ha-1 (Table 3-4 and 3-5).
Two higher rates of AG Crabgrass Killer (977 and 1465 kg ha-1) applied to wet foliage
provided ≥ 70% control 7 DAA (Table 3-4 and 3-5). Borax did not offer ≥ 64% control at
any leaf stage in either trial 7 DAA (Table 3-4 and 3-5).
For most treatments, southern crabgrass control decreased between 7 DAA and
21 DAA. Asulam was the only treatment that provided ≥ 70% control of 1-2 and 3-4 leaf
crabgrass at 21 DAA in Trial II (Table 3-7). No treatment achieved ≥ 70% control of 1-2
tiller stage crabgrass 21 DAA.
Products in these trials are generally not manufactured for use as herbicides.
Inconsistent control can result from the inability of products to remain on leaf surfaces,
especially in the case of sodium bicarbonate applied directly to plants in a powder form.
Borax and vinegar applied as a spray in a liquid form were not mixed with any
surfactants, which may have limited the amount of product that remained on the leaf
surfaces. The impact of surfactants added to these products has not been evaluated.
When applied to the leaf surface, the products tended to bead up on the cuticle of the
crabgrass leaf. Surfactants are added to decrease surface tension of water droplets,
leading to more material coming into contact to the leaf surface and possibly increasing
control (Jansen et al. 1961). When using contact materials, the effectiveness of the
product often correlates with the amount that comes in contact with the leaf surface.
52
Differences in control between trials and growth stages may be explained by water
droplet properties and contact with the leaf surface.
Shoot dry weights
There was a trial by treatment and growth stage by treatment interaction; therefore
data are shown separately. Significant shoot weight differences were seen in both trials
for most treatments applied at the 1-2 leaf stage. Shoot weights were less for
treatments at the 3-4 leaf stage and decreased even more at the 1-2 tiller stage.
Vinegar provided significantly lower shoot weights compared to the untreated in both
trials when applied at the 1-2 leaf stage (Table 3-8 and 3-9). Increased rates or multiple
applications of vinegar at any growth stage did not reduce shoot weights more than
single applications at lower rates in both trials with the exception of 281 L ha-1 rate in
2009 (Table 3-8). This is similar to what was observed with visual ratings, where control
did not differ between treatments for applications made at later growth stages (Table 3-
4). The use of sodium bicarbonate products resulted in significantly lower crabgrass
shoot dry weights than untreated plants when applied at the 1-2 leaf stage (Table 3-8
and 3-9). Higher rates (≥977 kg ha-1) of AG Crabgrass Killer generally reduced shoot
weights the most, while lower rates (≤488 kg ha-1) of AG Crabgrass Killer and sodium
bicarbonate resulted in higher shoot weights than the higher treatments. No consistent
differences were observed whether sodium bicarbonate products were applied to wet
versus dry foliage. The shoot weight results were consistent with those obtained from
visual ratings, were higher rates of AG Crabgrass Killer provided better crabgrass
control (Table 3-4 and 3-5). Borax treatments reduced shoot weights only when applied
at the 1-2 leaf stage (Table 3-8 and 3-9). There were no consistent differences between
rate of borax and shoot dry weight. These results were similar to visual evaluations of
53
crabgrass control from borax applied in greenhouse trials (Table 3-4 and 3-6). Asulam
had the greatest effect on reducing shoot weight at the two smaller growth stages of any
treatment in Trial II (Table 3-9). Shoot weight reductions of asulam were comparable to
other treatments when applied to larger crabgrass stages.
The differences in dry shoot weights between the two studies could be attributed
to fluctuations in temperatures. Both trials were conducted in an opaque greenhouse in
Jay, FL. Temperatures during trial dates fluctuated from a low of 15 C at night to a high
of 35 C during the day. In Trial I, there was a large difference between shoot weights
from different growth stages, especially at 1-2 leaf stage. An explanation could be that
crabgrass for the larger weed stages (3-4 leaf and 1-2 tiller) was grown during the
months of June and July, when crabgrass growth is optimal. Crabgrass used for the 1-2
leaf treatments was planted in August, and treatments extended into September. In
Trial II, crabgrass was planted in May and treatments for each crabgrass growth stage
were applied in succession throughout the month. The late planting in August of
crabgrass used for the 1-2 leaf treatments in Trial I may have affected crabgrass
growth, leading to slower growth and lower shoot weights.
Alternative Herbicide Field Evaluation
Crabgrass control
There was an interaction between treatments and years and treatments and
growth stages for field trials; therefore data were analyzed separately for both trials and
all stages of growth. The data presented were collected at either 7 or 21 DAA for
comparison to greenhouse trials. No treatment provided an acceptable level (≥ 70 %)
crabgrass control at either stage when evaluated 21 DAA for both years.
54
At the 1-2 leaf stage, sodium bicarbonate and AG Crabgrass Killer applied at 488
and 1465 kg ha-1 provided ≥ 45 % control both years when evaluated 7 DAA (Table 3-10
and Table 3-11). By 21 DAA, ≥ 50 % control was achieved in both years by AG
Crabgrass Killer applied at ≥ 488 kg ha-1 (Table 3-12 and Table 3-13). All other
treatments provided < 50% control in at least one of the years observed.
When compared to results from greenhouse trials, all vinegar treatments had
control levels of >10% lower in the field. A possible explanation is the height difference
between crabgrass and St. Augustinegrass at the different weed stages. St.
Augustinegrass used in the study was maintained at approximately 7.5 cm. At the 1-2
leaf stage, crabgrass is approximately 4-5 cm in height. The higher height of St.
Augustinegrass may have prevented even coverage of crabgrass foliage, reducing the
effectiveness of the vinegar treatments. Sodium bicarbonate products also showed
consistently less control in field trials than greenhouse trials. These products are
applied directly to plant foliage in a powder form and must retain contact with the leaf
surface to have activity. Because field conditions have greater environmental variability
(i.e., wind and rainfall), the product was more likely to be blown or washed off the leaf
surface, causing reductions in control. As with vinegar and sodium bicarbonate, borax
treatments were also not as effective in field trials for crabgrass control. For most
ratings, control was <10% for both leaf stages. The decrease in effectiveness could
again be due to different environmental factors.
Southern crabgrass is a summer annual and begins to senesce as day and night
temperatures begin to decrease in the fall (Uva et al. 1997). As temperatures fall,
crabgrass populations begin to decline as they complete their life cycle. Treatments for
55
the 1-2 tiller growth stage in 2009 were applied on August 4. Decreasing temperature
and crabgrass plants that are completing their life cycle may explain the increase in
crabgrass control. This would indicate that the effectiveness of the products is not
increasing; rather, increased control is a result of naturally declining weed populations.
St. Augustinegrass tolerance
There was an interaction between treatments and years and treatments and
growth stages for field trials; therefore, data were analyzed separately for both trials and
all stages of growth. The data presented were taken either at 7 or 21 DAA because
they represent injury observed after the product had a short period of time to interact
with St. Augustinegrass (7 DAA) and the relative rate of turf recovery over time (21
DAA).
For most turfgrass applications, 20% turfgrass injury is considered a maximum
acceptable threshold. In this study, any injury > 20% would be considered
unacceptable. At 7 DAA borax was the only product that was rated at <15% St.
Augustinegrass injury when applied to 1-2 leaf stage crabgrass (Table 3-14 and Table
3-15). All vinegar, sodium bicarbonate, and AG Crabgrass Killer treatments caused
unacceptable levels of injury when applied to 1-2 leaf stage crabgrass. At the 1-2 tiller
crabgrass stage, turfgrass injury was ≥ 15% for all rates of vinegar, sodium bicarbonate
and AG Crabgrass Killer at 1465 kg ha-1 in 2009. Unacceptable levels of injury
occurred both years from all treatments of vinegar and sodium bicarbonate.
By 21 DAA, turfgrass injury was <15% for all treatments in both years (Table 3-16
and Table 3-17). Injury levels in 2009 were unacceptable for vinegar applied in multiple
applications (> 50%), but injury was ≤ 5% in 2010 for the same treatment. When
applied at the 1-2 tiller stage of crabgrass growth, both multiple application treatments
56
of vinegar, sodium bicarbonate, and AG Crabgrass Killer at 1465 kg ha-1 caused ≥ 15%
injury both years. Multiple applications of vinegar caused unacceptable injury in both
years, while single applications of vinegar had unacceptable injury levels only in 2009
(Table 3-16). All sodium bicarbonate products treatments (including AG Crabgrass
Killer) were acceptable in 2009 (Table 3-16). In 2010, injury was unacceptable only
when applied at 1465 kg ha-1 (Table 3-17).
Differences in turfgrass injury between years may be due to the age of the St.
Augustinegrass used for these studies. Turfgrass injury can be prolonged if applied to
newly sodded turf (McCarty et al. 1995). The St. Augustinegrass block utilized for these
studies was sodded in March of 2009 and the 2009 treatments were applied to relatively
new established turf. By 2010, the turfgrass was well established.
Periods of dry weather and other environmental factors could also delay turf
recovery. In 2009, crabgrass overseeding was delayed due to turf establishment;
therefore, 1-2 leaf treatments were applied July 9 and 1-2 tiller treatments on August 4.
In 2010, 1-2 leaf treatments were applied on May 5, with 1-2 tiller treatments applied on
June 8. The difference in timings may have impacted the level and duration of St.
Augustinegrass injury observed. The month of June in Florida is often characterized by
high temperatures and dry conditions. The most prolonged injury was seen from
treatments applied in June and July. The environmental conditions during these months
including high temperatures may explain higher levels of initial and prolonged turfgrass
injury.
AG Crabgrass Killer Ingredient Evaluation
A treatment by growth stage interaction was observed for crabgrass control;
therefore, growth stages are shown separately. At the 1-2 leaf stage, both rates of AG
57
Crabgrass Killer and the sodium bicarbonate applied at 967 kg ha-1 provided ≥ 70%
crabgrass control (Table 3-18). For most treatments, control was less at the 3-4 leaf
stage than the 1-2 leaf stage. AG Crabgrass Killer and sodium bicarbonate did not
provided acceptable control, when applied to 3-4 leaf stage crabgrass. Cinnamon and
cumin did not provide acceptable crabgrass control when applied to either growth stage.
There was no interaction between treatments and growth stages for crabgrass dry
weight; therefore data were pooled from each growth stage. Shoot dry weights that
were different from the untreated control included both rates of AG Crabgrass Killer and
sodium bicarbonate, and cinnamon applied at 9.3 kg ha-1 (Table 3-19). Both rates of
AG Crabgrass Killer and sodium bicarbonate had lower shoot weights than any other
treatment.
Cinnamon is labeled as the active ingredient in Crabgrass Killer, with all other
materials tested listed as inert ingredients (Anonymous 2005). Only treatments
containing sodium bicarbonate provided any crabgrass control at both leaf stages.
Cumin and cinnamon showed inconsistent control and generally insignificant changes in
crabgrass shoot dry weight. The results did show an increase in weed control with a
combination of cinnamon, sodium bicarbonate and cumin. Another product on the label
is wheat and corn flour, though neither have been reported to have herbicidal properties
for postemergence control (Anonymous 2005). The flour components may have been
added to improve handling characteristics and improve efficiency. When sodium
bicarbonate was applied separately, it tended to clump with moisture and does not
adhere well to the leaf surface. AG Crabgrass Killer does adhere to the leaf surface
well, even when moisture is present. The addition of flour in the formulation appears to
58
improve the ability of AG Crabgrass Killer to remain on the leaf, which may lead to an
increase in efficacy of sodium bicarbonate due to increased surface contact.
Summary
Because of the lack of synthetic postemergence herbicide options available to
homeowners for southern crabgrass control in St. Augustinegrass, alternative
herbicides are being considered in management strategies. Recent shifts in public
opinion have also increased interest and demand for organic options for weed control,
particularly in home lawn situations.
Sodium bicarbonate, vinegar, and borax were all considered due to previous
research showing herbicidal activity of these materials. Greenhouse trials showed that
crabgrass was controlled by these products when applied to the smallest growth stage
tested. Repeat applications of vinegar and AG Crabgrass Killer were initially effective,
but crabgrass recovered after a few weeks. Asulam, a synthetic herbicide included for
comparison, was the only treatment to maintain acceptable levels of crabgrass control
over time. In field trials, no alternative herbicide tested provided lasting control of
southern crabgrass. Because of recovery patterns in crabgrass, additional trials need to
be conducted testing multiple applications of sodium bicarbonate products.
Vinegar and sodium bicarbonate were both very injurious to St. Augustinegrass.
Recovery was rapid for most vinegar applications and turf injured by sodium
bicarbonate products was slower to recover. If used, both products would have to be
used as spot treatments in highly infested areas due to high injury levels to turfgrass.
If alternative herbicides are used for southern crabgrass management, control
levels of ≥ 70% should not be expected from any of the products tested. They can be
used as a means of suppression, and used with other weed management practices. If
59
utilized they would have to be applied to small crabgrass growth, preferably at or
immediately after emergence for control.
60
Table 3-1. Alternative herbicide treatments for greenhouse evaluation. Treatment Rate
1 Untreated
2 300 Grain Vinegara 187 L ha-1
3 300 Grain Vinegara 187 L ha-1
+ 300 Grain Vinegar + 187 L ha-1
4 300 Grain Vinegara 281 L ha-1
5 300 Grain Vinegara 281 L ha-1
+ 300 Grain Vinegar + 281 L ha-1
6 300 Grain Vinegara 374 L ha-1
7 AG Crabgrass Killercd 244 kg ha-1
8 AG Crabgrass Killercd 488 kg ha-1
9 AG Crabgrass Killercd 977 kg ha-1
10 AG Crabgrass Killercd 1465 kg ha-1
11 Sodium Bicarbonated 1465 kg ha-1
12 AG Crabgrass Killerce 244 kg ha-1
13 AG Crabgrass Killerce 488 kg ha-1
14 AG Crabgrass Killerce 977 kg ha-1
15 AG Crabgrass Killerce 1465 kg ha-1
16 Sodium Bicarbonatee 1465 kg ha-1
17 Boraxb 15 kg ha-1
18 Boraxb 30 kg ha-1
19 Boraxb 61 kg ha-1
aacetic acid - 30%
bborax - 99.5%
cactive – cinnamon - 0.95%, inert – sodium bicarbonate, corn and wheat flour, cumin - 99.1%
dwet
edry
61
Table 3-2. Alternative herbicide treatments for field evaluation. Treatment Rate
1 Untreated
2 300 Grain Vinegara 187 L ha-1
3 300 Grain Vinegara 187 L ha-1
+ 300 Grain Vinegar + 187 L ha-1
4 300 Grain Vinegara 281 L ha-1
5 300 Grain Vinegara 281 L ha-1
+ 300 Grain Vinegar + 281 L ha-1
6 300 Grain Vinegar 374 L ha-1
7 AG Crabgrass Killerc 244 kg ha-1
8 AG Crabgrass Killerc 488 kg ha-1
9 AG Crabgrass Killerc 977 kg ha-1
10 AG Crabgrass Killerc 1465 kg ha-1
11 Sodium Bicarbonate 1465 kg ha-1
12 Boraxb 15 kg ha-1
13 Boraxb 30 kg ha-1
14 Boraxb 61 kg ha-1
aacetic acid - 30%
bborax - 99.5%
cactive – cinnamon - 0.95%, inert – sodium bicarbonate, corn and wheat flour, cumin - 99.1%
Table 3-3. Treatments for AG Crabgrass Killer ingredient evaluation. Treatment Rate
1 Untreated
2 Cinnamon 4.6 kg ha-1
3 Cinnamon 9.3 kg ha-1
4 Sodium Bicarbonate 484 kg ha-1
5 Sodium Bicarbonate 967 kg ha-1
6 Crabgrass Killera 488 kg ha-1
7 Crabgrass Killera 977 kg ha-1
8 Cumin 9.3 kg ha-1 aactive – cinnamon - 0.95%, inert – sodium bicarbonate, corn and wheat flour, cumin - 99.1%
62
Table 3-4. Crabgrass control with alternative herbicides in the
greenhouse 7 days after application - Trial I. Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 3-4 Leaf 1-2 Tiller
-----------% Control---------
Untreated 0 kg ha-1 0 0 0
300 Grain Vinegar 187 L ha-1 63 5 2
+ 300 Grain Vinegar + 187 L ha-1 62 5 10
300 Grain Vinegar 187 L ha-1 300 Grain Vinegar 281 L ha-1 57 10 15
300 Grain Vinegar 281 L ha-1 87 13 15
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 95 15 15
AG Crabgrass Killera 244 kg ha-1 23 0 13
AG Crabgrass Killera 488 kg ha-1 56 5 20
AG Crabgrass Killera 977 kg ha-1 81 31 25
AG Crabgrass Killera 1465 kg ha-1 91 66 26
Sodium Bicarbonatea 1465 kg ha-1 26 16 18
AG Crabgrass Killerb 244 kg ha-1 40 14 6
AG Crabgrass Killerb 488 kg ha-1 68 23 11
AG Crabgrass Killerb 977 kg ha-1 89 24 20
AG Crabgrass Killerb 1465 kg ha-1 73 31 34
Sodium Bicarbonateb 1465 kg ha-1 43 19 19
Borax 15 kg ha-1 11 18 5
Borax 30 kg ha-1 6 13 6
Borax 61 kg ha-1 9 10 19
LSD (0.05) 22 10 6
CV% 30 40 28 awet
bdry
63
Table 3-5. Crabgrass control with alternative herbicides in the greenhouse
7 days after application - Trial II. Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 3-4 Leaf 1-2 Tiller
-----------% Control---------
Untreated 0 kg ha-1 0 0 0
300 Grain Vinegar 187 L ha-1 38 13 10
+ 300 Grain Vinegar + 187 L ha-1 46 28 6
300 Grain Vinegar 187 L ha-1 300 Grain Vinegar 281 L ha-1 64 48 15
300 Grain Vinegar 281 L ha-1 83 59 20
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 55 24 25
AG Crabgrass Killera 244 kg ha-1 38 13 9
AG Crabgrass Killera 488 kg ha-1 50 19 5
AG Crabgrass Killera 977 kg ha-1 75 38 16
AG Crabgrass Killera 1465 kg ha-1 85 45 18
Sodium Bicarbonatea 1465 kg ha-1 49 11 20
AG Crabgrass Killerb 244 kg ha-1 44 10 4
AG Crabgrass Killerb 488 kg ha-1 55 8 10
AG Crabgrass Killerb 977 kg ha-1 48 14 8
AG Crabgrass Killerb 1465 kg ha-1 65 14 6
Sodium Bicarbonateb 1465 kg ha-1 44 16 11
Borax 15 kg ha-1 11 4 4
Borax 30 kg ha-1 35 14 5
Borax 61 kg ha-1 64 15 6
Asulam 2.3 kg ha-1 39 15 5
LSD (0.05) 14 10 9
CV% 20 36 63 awet
bdry
64
Table 3-6. Crabgrass control with alternative herbicides in the greenhouse 21
days after application - Trial I. Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 3-4 Leaf 1-2 Tiller
-----------% Control---------
Untreated 0 kg ha-1 0 0 0
300 Grain Vinegar 187 L ha-1 53 7 5
+ 300 Grain Vinegar + 187 L ha-1 55 10 7
300 Grain Vinegar 187 L ha-1 300 Grain Vinegar 281 L ha-1 37 18 5
300 Grain Vinegar 281 L ha-1 67 23 17
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 95 10 15
AG Crabgrass Killera 244 kg ha-1 25 10 5
AG Crabgrass Killera 488 kg ha-1 39 10 9
AG Crabgrass Killera 977 kg ha-1 88 21 14
AG Crabgrass Killera 1465 kg ha-1 93 36 18
Sodium Bicarbonatea 1465 kg ha-1 45 19 9
AG Crabgrass Killerb 244 kg ha-1 39 10 6
AG Crabgrass Killerb 488 kg ha-1 65 21 6
AG Crabgrass Killerb 977 kg ha-1 87 19 12
AG Crabgrass Killerb 1465 kg ha-1 83 18 14
Sodium Bicarbonateb 1465 kg ha-1 43 8 8
Borax 15 kg ha-1 34 5 5
Borax 30 kg ha-1 25 5 6
Borax 61 kg ha-1 33 13 9
LSD (0.05) 27 4 4
CV% 35 21 31 awet
bdry
65
Table 3-7. Crabgrass control with alternative herbicides in the greenhouse
21 days after application - Trial II. Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 3-4 Leaf 1-2 Tiller
-----------% Control---------
Untreated 0 kg ha-1 0 0 0
300 Grain Vinegar 187 L ha-1 20 3 3
+ 300 Grain Vinegar + 187 L ha-1 29 3 3
300 Grain Vinegar 187 L ha-1 300 Grain Vinegar 281 L ha-1 44 15 1
300 Grain Vinegar 281 L ha-1 45 19 1
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 49 4 4
AG Crabgrass Killera 244 kg ha-1 15 0 1
AG Crabgrass Killera 488 kg ha-1 16 0 0
AG Crabgrass Killera 977 kg ha-1 31 6 5
AG Crabgrass Killera 1465 kg ha-1 52 8 4
Sodium Bicarbonatea 1465 kg ha-1 24 0 7
AG Crabgrass Killerb 244 kg ha-1 11 0 0
AG Crabgrass Killerb 488 kg ha-1 10 0 2
AG Crabgrass Killerb 977 kg ha-1 18 1 1
AG Crabgrass Killerb 1465 kg ha-1 20 0 5
Sodium Bicarbonateb 1465 kg ha-1 10 5 3
Borax 15 kg ha-1 5 0 3
Borax 30 kg ha-1 8 1 3
Borax 61 kg ha-1 19 4 5
Asulam 2.3 kg ha-1 87 74 50
LSD (0.05) 12 6 10
CV% 32 56 146 awet
bdry
66
Table 3-8. Crabgrass shoot dry weights - Trial I. Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 3-4 Leaf 1-2 Tiller
---------Dry Weight (g)--------
Untreated 0 kg ha-1 1.01 40.46 32.48
300 Grain Vinegar 187 L ha-1 0.01 47.97 24.30
+ 300 Grain Vinegar + 187 L ha-1 0.02 49.40 20.99
300 Grain Vinegar 187 L ha-1 300 Grain Vinegar 281 L ha-1 0.66 52.97 30.13
300 Grain Vinegar 281 L ha-1 0.02 41.45 22.78
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 0.04 40.40 28.50
AG Crabgrass Killera 244 kg ha-1 0.32 33.70 25.98
AG Crabgrass Killera 488 kg ha-1 0.49 37.65 23.48
AG Crabgrass Killera 977 kg ha-1 0.01 26.95 23.93
AG Crabgrass Killera 1465 kg ha-1 0.01 13.53 11.75
Sodium Bicarbonatea 1465 kg ha-1 0.10 31.21 25.00
AG Crabgrass Killerb 244 kg ha-1 0.02 39.53 23.15
AG Crabgrass Killerb 488 kg ha-1 0.22 28.30 29.50
AG Crabgrass Killerb 977 kg ha-1 0.01 31.48 28.28
AG Crabgrass Killerb 1465 kg ha-1 0.17 20.93 17.60
Sodium Bicarbonateb 1465 kg ha-1 0.13 35.75 22.43
Borax 15 kg ha-1 0.19 44.55 36.88
Borax 30 kg ha-1 0.14 46.85 38.44
Borax 61 kg ha-1 0.47 39.55 19.50
LSD (0.05) 0.54 12.24 13.34
CV% 168 23 35 awet
bdry
67
Table 3-9. Crabgrass shoot dry weights - Trial II. Growth Stage
Treatment Rate 1-2 Leaf 3-4 Leaf 1-2 Tiller
---------Dry Weight (g)--------
Untreated 0 kg ha-1 10.48 15.60 17.00
300 Grain Vinegar 187 L ha-1 6.28 11.30 17.95
+ 300 Grain Vinegar 187 L ha-1 6.26 9.05 18.10
300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 6.95 7.95 15.60
300 Grain Vinegar 281 L ha-1 5.40 7.85 18.58
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 6.90 11.45 18.85
AG Crabgrass Killera 244 kg ha-1 7.65 10.40 16.53
AG Crabgrass Killera 488 kg ha-1 5.70 9.50 14.85
AG Crabgrass Killera 977 kg ha-1 4.98 9.03 17.83
AG Crabgrass Killera 1465 kg ha-1 6.25 10.78 15.03
Sodium Bicarbonatea 1465 kg ha-1 8.48 13.93 17.88
AG Crabgrass Killerb 244 kg ha-1 7.65 14.58 19.43
AG Crabgrass Killerb 488 kg ha-1 5.28 12.83 16.93
AG Crabgrass Killerb 977 kg ha-1 6.01 13.45 17.40
AG Crabgrass Killerb 1465 kg ha-1 4.53 13.30 18.10
Sodium Bicarbonateb 1465 kg ha-1 7.33 8.20 16.35
Borax 15 kg ha-1 11.00 17.30 17.30
Borax 30 kg ha-1 6.93 12.33 16.45
Borax 61 kg ha-1 5.65 13.15 15.80
Asulam 2.3 kg ha-1 0.33 1.90 15.53
LSD (0.05) 2.14 3.49 ns
CV% 23 22 22 awet
bdry
68
Table 3-10. Crabgrass control in the field with alternative herbicides 7 days after
application - 2009.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
----% Control----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 13 72
Borax 30 kg ha-1 8 73
Borax 61 kg ha-1 10 70
AG Crabgrass Killer 244 kg ha-1 43 55
AG Crabgrass Killer 488 kg ha-1 52 52
AG Crabgrass Killer 977 kg ha-1 58 47
AG Crabgrass Killer 1465 kg ha-1 52 23
Sodium Bicarbonate 1465 kg ha-1 52 52
300 Grain Vinegar 187 L ha-1 35 48
300 Grain Vinegar 187 L ha-1 30 47
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 38 48
300 Grain Vinegar 281 L ha-1 35 43
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 10 48
LSD (0.05) 10 37
CV% 18 19
69
Table 3-11. Crabgrass control in the field with alternative herbicides 7 days after
application – 2010.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
----% Control----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 2 2
Borax 30 kg ha-1 3 5
Borax 61 kg ha-1 7 5
AG Crabgrass Killer 244 kg ha-1 46 20
AG Crabgrass Killer 488 kg ha-1 53 27
AG Crabgrass Killer 977 kg ha-1 45 42
AG Crabgrass Killer 1465 kg ha-1 58 50
Sodium Bicarbonate 1465 kg ha-1 50 41
300 Grain Vinegar 187 L ha-1 42 17
300 Grain Vinegar 187 L ha-1 51 78
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 45 28
300 Grain Vinegar 281 L ha-1 48 78
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 48 45
LSD (0.05) 13 18
CV% 22 34
70
Table 3-12. Crabgrass control in the field with alternative herbicides 21 days after
application - 2009.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
----% Control----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 7 72
Borax 30 kg ha-1 0 75
Borax 61 kg ha-1 0 78
AG Crabgrass Killer 244 kg ha-1 18 57
AG Crabgrass Killer 488 kg ha-1 55 62
AG Crabgrass Killer 977 kg ha-1 50 53
AG Crabgrass Killer 1465 kg ha-1 59 74
Sodium Bicarbonate 1465 kg ha-1 32 65
300 Grain Vinegar 187 L ha-1 35 45
300 Grain Vinegar 187 L ha-1 20 50
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 23 45
300 Grain Vinegar 281 L ha-1 27 35
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 32 52
LSD (0.05) 26 20
CV% 61 34
71
Table 3-13. Crabgrass control in the field with alternative herbicides 21 days after
application - 2010.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
----% Control----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 3 0
Borax 30 kg ha-1 3 2
Borax 61 kg ha-1 5 5
AG Crabgrass Killer 244 kg ha-1 52 15
AG Crabgrass Killer 488 kg ha-1 53 10
AG Crabgrass Killer 977 kg ha-1 50 18
AG Crabgrass Killer 1465 kg ha-1 57 27
Sodium Bicarbonate 1465 kg ha-1 55 10
300 Grain Vinegar 187 L ha-1 27 8
300 Grain Vinegar 187 L ha-1 42 20
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 22 15
300 Grain Vinegar 281 L ha-1 43 12
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 35 25
LSD (0.05) 16 14
CV% 29 72
72
Table 3-14. St. Augustinegrass injury from alternative herbicides 7 days after
application – 2009.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
-----% Injury-----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 5 0
Borax 30 kg ha-1 8 0
Borax 61 kg ha-1 10 0
AG Crabgrass Killer 244 kg ha-1 28 7
AG Crabgrass Killer 488 kg ha-1 40 8
AG Crabgrass Killer 977 kg ha-1 50 8
AG Crabgrass Killer 1465 kg ha-1 47 17
Sodium Bicarbonate 1465 kg ha-1 53 20
300 Grain Vinegar 187 L ha-1 62 27
300 Grain Vinegar 187 L ha-1 60 18
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 62 23
300 Grain Vinegar 281 L ha-1 55 22
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 55 27
LSD (0.05) 14 7
CV% 21 32
73
Table 3-15. St. Augustinegrass injury from alternative herbicides 7 days after
application – 2010.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
-----% Injury-----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 3 2
Borax 30 kg ha-1 5 10
Borax 61 kg ha-1 10 8
AG Crabgrass Killer 244 kg ha-1 18 23
AG Crabgrass Killer 488 kg ha-1 32 32
AG Crabgrass Killer 977 kg ha-1 53 53
AG Crabgrass Killer 1465 kg ha-1 58 65
Sodium Bicarbonate 1465 kg ha-1 58 72
300 Grain Vinegar 187 L ha-1 42 30
300 Grain Vinegar 187 L ha-1 42 93
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 45 35
300 Grain Vinegar 281 L ha-1 47 95
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 45 45
LSD (0.05) 13 12
CV% 23 18
74
Table 3-16. St. Augustinegrass injury from alternative herbicides 21 days after
application – 2009.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
-----% Injury-----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 2 2
Borax 30 kg ha-1 0 2
Borax 61 kg ha-1 0 3
AG Crabgrass Killer 244 kg ha-1 6 8
AG Crabgrass Killer 488 kg ha-1 14 8
AG Crabgrass Killer 977 kg ha-1 13 15
AG Crabgrass Killer 1465 kg ha-1 11 15
Sodium Bicarbonate 1465 kg ha-1 13 18
300 Grain Vinegar 187 L ha-1 15 38
300 Grain Vinegar 187 L ha-1 53 43
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 12 20
300 Grain Vinegar 281 L ha-1 57 52
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 17 23
LSD (0.05) 10 22
CV% 38 75
75
Table 3-17. St. Augustinegrass injury from alternative herbicides 21 days after
application – 2010.
Crabgrass Growth Stage
Treatment Rate 1-2 Leaf 1-2 Tiller
-----% Injury-----
Untreated 0 kg ha-1 0 0
Borax 15 kg ha-1 0 0
Borax 30 kg ha-1 0 0
Borax 61 kg ha-1 0 0
AG Crabgrass Killer 244 kg ha-1 0 5
AG Crabgrass Killer 488 kg ha-1 0 12
AG Crabgrass Killer 977 kg ha-1 0 10
AG Crabgrass Killer 1465 kg ha-1 3 25
Sodium Bicarbonate 1465 kg ha-1 0 40
300 Grain Vinegar 187 L ha-1 0 8
300 Grain Vinegar 187 L ha-1 3 33
+ 300 Grain Vinegar + 187 L ha-1 300 Grain Vinegar 281 L ha-1 0 10
300 Grain Vinegar 281 L ha-1 5 42
+ 300 Grain Vinegar + 281 L ha-1 300 Grain Vinegar 374 L ha-1 0 5
LSD (0.05) 4 11
CV% 181 46
76
Table 3-18. Postemergence crabgrass control with Crabgrass Killer ingredients 14 days after application.
Rate Crabgrass Growth Stage
Treatment (kg ha-1) 1-2 Leaf 3-4 Leaf
-----% Control-----
Untreated 0 0 0
Cinnamon 4.6 0 3
Cinnamon 9.3 0 0
Sodium Bicarbonate 484 33 19
Sodium Bicarbonate 967 70 11
Crabgrass Killer 488 75 29
Crabgrass Killer 977 84 28
Cumin 9.3 23 0
LSD (0.05) 37 10
CV% 72 64
Table 3-19. Shoot dry weights as influenced by AG Crabgrass Killer ingredients.
Treatment Rate (kg ha-1) Weight (g)
Untreated 0 9.35
Cinnamon 4.6 9.63
Cinnamon 9.3 5.46
Sodium Bicarbonate 484 4.96
Sodium Bicarbonate 967 4.84
Crabgrass Killer 488 3.65
Crabgrass Killer 977 4.13
Cumin 9.3 9.14
LSD (0.05) 3.57
CV% 56
77
APPENDIX
FIGURES AND TABLES FROM REMOTE SENSING DATA
No Irrigation ET Irrigation Daily Irrigation
% V
WC
0
5
10
15
20
25
30
35
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 4-1. Percent volumetric water content based on irrigation and nitrogen fertility in
Jay, FL on July 21, 2010.
Mowing Height
5 cm 7.5 cm 10 cm
Chlo
rophyll
Count
0
50
100
150
200
250
300
350
0 kg ha-1
98 kg ha-1
146 kg ha-1
195 kg ha-1
Figure 4-2. Chlorophyll count based on mowing height and nitrogen fertility in Jay, FL
on July 22, 2009.
78
Mowing Height
5 cm 7.5 cm 10 cm
Chlo
rophyll
Count
0
50
100
150
200
250
300
350
0 kg N ha-1
98 kg N ha-1
146 kg N ha-1
195 kg N ha-1
Figure 4-3. Chlorophyll count based on mowing height and nitrogen fertility in Jay, FL
on July 21, 2010.
79
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BIOGRAPHICAL SKETCH
Brian Glenn is the son of Robert Glenn and Catherine Christianson. He grew up in
Texas and southern California. Brian graduated from high school in 2001, then enrolled
at Brigham Young University in Provo, Utah. He took a two year break from school in
2002 for a service mission for his church to southern Chile. After his return, he married
Rachel Eynon in 2007, and graduated in 2008 with a Bachelor of Science degree in
landscape management. He also earned his CLP (Certified Landscape Professional)
while in school. Brian completed his masters at the University of Florida in the spring of
2011, focusing on weed management in turfgrass. He plans to pursue a doctorate from
the University of Florida focused on research dealing with improving turf management
strategies.