research article selective herbicides for cultivation of...

Research ArticleSelective Herbicides for Cultivation ofEucalyptus urograndis Clones

Patrick J Minogue and Anna Osiecka

University of Florida North Florida Research and Education Center Quincy FL 32351 USA

Correspondence should be addressed to Patrick J Minogue pminogueufledu

Received 17 January 2015 Revised 16 April 2015 Accepted 20 April 2015

Academic Editor Guy R Larocque

Copyright copy 2015 P J Minogue and A OsieckaThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

Competition control is essential for successful eucalyptus plantation establishment yet few selective herbicides have been identifiedFive herbicides flumioxazin imazamox imazapic oxyfluorfen and sulfometuronmethyl were evaluated for selective weed controlin the establishment of genetically modified frost tolerant Eucalyptus urograndis clones Herbicides were applied at two or threerates either before or after weed emergence and compared to a nontreated control and to near-complete weed control obtainedwith glyphosate directed sprays Applications prior to weed emergence were most effective for weed control and with the exceptionof imazapic all resulted in enhanced eucalyptus growth relative to the nontreated control Among postemergent treatments onlyimazamox enhanced stem volume Among selective herbicide treatments preemergent 2240 g haminus1 oxyfluorfen produced the bestgrowth response resulting in stem volume index that was 860 greater than the nontreated control although only 15 of thevolume index obtained with near-complete weed control Imazapic was the most phytotoxic of all herbicides resulting in 40mortality when applied preemergent Survival was 100 for all other herbicide treatments This research found the previouslynontested herbicides imazamox and imazapic to be effective for selective weed control and refined application rate and timing offive herbicides for use in clonal plantations

1 Introduction

Because of their adaptability and fast growth rates Eucalyptusspecies and hybrids have been grown for fiber fuel landscap-ing mulch essential oils phytoremediation and as ornamen-tal trees [1 2] on more than 178 million ha worldwide [3]Few silvicultural guidelines for eucalyptus plantations in thesouthern US have been published but vegetation manage-ment during stand establishment and nutrient managementare known to be critical to success [4 5] In summarizingexperience with eucalyptus plantings in this region Kellisonet al [5] ldquohighlyrdquo recommended that plantations be kept freefrom competition for at least the first two growing seasonsThe importance of vegetation management prior to plantingeucalyptus is stressed by many authors [6 7] and studiesthroughout the world have demonstrated that competitionin the first eighteen months to two years following plantingis most impactful [8ndash10] as fast growing eucalyptus trees attypical plantation densities (3 by 35m) quickly close crowncanopy excluding light to the understory thus limiting the

growth of other vegetation Because trees under stress fromweed pressure or limited nutrients are more susceptible tocold injury than those without these limitations [11 12] con-trolling competition may also impart greater cold tolerancean important consideration in temperate climates

A limited number of herbicides are used in eucalyptusculture worldwide and even fewer are specifically labeledfor eucalyptus plantation silviculture by various regulatoryagencies [7] There are more alternative herbicides for usein site preparation than in established stands where greaterherbicide selectivity is needed The development of a selec-tive broad spectrum herbicide which can be sprayed overeucalyptus transplants and provide persistent weed controlwhen applied either prior to weed emergence (preemergent)or to actively growing weeds (postemergent) would advanceeucalyptus silviculture

The nonselective herbicide glyphosate controls a broadweed spectrum and is widely used to prepare sites forplanting and applied after planting using shielded or directed

Hindawi Publishing CorporationInternational Journal of Forestry ResearchVolume 2015 Article ID 341314 12 pageshttpdxdoiorg1011552015341314

2 International Journal of Forestry Research

sprays to avoid eucalyptus foliage contact Because glyphosatedoes not provide soil residual herbicide activity applicationsprior to planting are not injurious to eucalyptus transplantsConversely applications after planting often reduce growthrates or cause significant injury or mortality because it isdifficult to eliminate drift in operational practice even withdirected sprays In their study of the effect of glyphosate spraydrift to eucalyptus clones Tuffi Santos et al [13] observed aprogression of injury symptoms from leaf chlorosis throughnecrosis to plant death with phytotoxicity positively corre-lated to increasing application rate Multiple applications ofglyphosate are needed through the growing season as newweeds emerge resulting in a significant cost [14] There arealso concerns regarding the development of resistant weedswhen a single herbicide or herbicides with a common modeof action are used particularly with repeated applications andhigh selection pressure

Oxyfluorfen and flumioxazin are selective herbicideswhichmay be applied over newly planted eucalyptus Oxyflu-orfen is effective as a pre- and early postemergence herbicideon small-seeded annual forbs and it suppresses annual grassesbut provides poor control of perennial grasses [15] Oxyflu-orfen is widely used in eucalyptus silviculture but currentproduct labels restrict applications to ldquodormantrdquo trees [16] acondition that may not exist in some climates because euca-lyptus have naked bud habit and are never truly dormant Flu-mioxazin is effective for forb and annual grass control whenapplied preemergence or at a very early stage of weed growth[16] but because of photodegradation this herbicide has shortresidual activity [15] Flumioxazin is labeled for use in ldquofieldgrown deciduous treesrdquo [16] but not specifically for eucalyp-tus plantations In a recent study in Brazil [17] flumioxazinrates ranging from 75 to 125 g active ingredient (ai) haminus1 wereexamined for selective weed control in newly planted Euca-lyptus grandisWHill exMaid clonesThe authors concludedthat flumioxazin is selective to eucalyptus at the highest ratetested but that combinations with other herbicides providedbetter weed control Research is needed to refine applicationrate and timing relative to stage of eucalyptus growth andweed development for both oxyfluorfen and flumioxazin

Sulfometuron methyl (hereafter referred to as sulfome-turon) is a soil residual herbicide providing selective weedcontrol with either pre- or postemergence applications ineucalyptus plantations although best efficacy is obtainedwhen weeds are in an early stage of growth Specific herbicidelabeling for eucalyptus plantations is currently limited [7]Sulfometuron is perhaps most promising as it is a longresidual herbicide and controls a broad spectrum of annualand perennial weeds however seedling injury is a seriousconcern where soil pH exceeds 6This is explained by greatersoil residual activity as degradation by hydrolysis is limitedin alkaline conditions [18] Blazer et al [14] found applica-tions of oxyfluorfen and sulfometuron to reduce competingvegetation and promote Eucalyptus macarthuriiH Dean andMaiden seedling height growth better than directed spraysof glyphosate but emphasized the need for future researchto define sulfometuron rate responses for various vegetationtypes and soils

Eucalyptus afforestation efforts by forest industry in thesouthern US have had limited success because of frost intol-erance [5 19] but there is renewed interest in planting cold-tolerant species hybrids and genetically modified cold hardyplanting stock to meet increasing hardwood fiber demandand to supply potential bioenergymarketsThe hybrid E uro-grandis a cross between E grandis and E urophylla ST Blakehas shown suitability for plantation culture in the southeast-ern US [5] Advanced breeding techniques including geneticmodification are being used to develop cold hardy cultivarssuch as Arborgenrsquos (Summerville South Carolina USA)ldquoFrost Tolerant Eucalyptusrdquo (FTE) E urograndis clones [20]Selective herbicides for FTE clones have not been identified

Preliminary experiments at our research center demon-strated the effectiveness of imazamox and imazapic herbi-cides for selective weed control in newly established eucalyp-tus plantations in north Florida although selectivity differedby herbicide rate application timing and Eucalyptus species[21] These herbicides have the advantage of being effectiveboth before and after weed emergence but provide varyingdegrees of residual weed control [15] This study examinesfour promising herbicides for selective weed control in euca-lyptus flumioxazin imazamox imazapic and sulfometuronrelative to the widely used oxyfluorfen operational standardto refine application rate and timing recommendations forselective weed control in two genetically modified frost-tolerant hybrid lines of Eucalyptus urograndis

Eucalyptus growth response to selective herbicide treat-ments reflects a balance between direct negative effects ofthe herbicide and the benefits of competition control Tobetter examine their selectivity herbicide treatments werecompared to two experimental controls one which was non-treated and one receiving near complete weed control usingcareful directed sprays of glyphosate The complete weedcontrol treatment demonstrates the potential for eucalyptusgrowth in the absence of competition and herbicide phyto-toxicity

2 Materials and Methods

21 Site Description The study site was a fallow agriculturalfield located at the University of Florida North FloridaResearch and Education Center south of the city of Quincyin the lower Coastal Plain region of Florida USA (30∘321015840N84∘351015840W) at an altitude of approximately 70mThe local cli-mate is temperate warm and wet with highest temperaturesin July (mean temperature 271∘C maximum temperature327∘C) lowest temperatures in January (mean tempera-ture 103∘C minimum temperature 40∘C) and 1431mmannual precipitation [22] The soil is a Dothan- (fine-loamykaolinitic and thermic Plinthic Kandiudults) Fuquay (loamykaolinitic and thermicArenic PlinthicKandiudults) complex[23]

22 Site Preparation and Plantation Establishment In Octo-ber 2008 the study site was prepared for planting by applying34 kg acid equivalent (ae) haminus1 glyphosate herbicide (RazorPro Nufarm Burr Ridge IL USA) as a broadcast spray and

International Journal of Forestry Research 3

Table 1 Herbicide treatments tested for selective weed control in Eucalyptus urograndis clonal plantation culture near Quincy Floridaapplied over the top of newly planted container-grown cuttings1 either prior to weed emergence (PRE two weeks after planting) or afterweed emergence (POST six weeks after planting) compared to a nontreated control and near complete weed control obtained using repeatedglyphosate herbicide sprays carefully directed to weeds while shielding seedlings from spray contact

Treatment Relative rate Actual rate2 (g haminus1) Trade name Herbicide contentFlumioxazin Low 290 ai SureGuard 51Flumioxazin High 430 ai SureGuard 51Imazamox3 Low 140 ae Clearcast 120 g Lminus1

Imazamox3 High 280 ae Clearcast 120 g Lminus1

Imazapic3 Low 140 ae Plateau 240 g Lminus1

Imazapic3 High 210 ae Plateau 240 g Lminus1

Oxyfluorfen Low 1120 ai GoalTender 480 g Lminus1

Oxyfluorfen High 2240 ai GoalTender 480 g Lminus1

Sulfometuron methyl Low 26 ai Oust XP 75Sulfometuron methyl Medium 53 ai Oust XP 75Sulfometuron methyl High 105 ai Oust XP 75Nontreated control mdash mdash mdash mdashComplete weed control mdash mdash Accord XRT mdash1Container grown rooted cuttings were sixteen weeks old at planting2Rate of active ingredient (ai) or acid equivalent (ae) applied3A nonionic surfactant was added at 025 (vv) for POST applications of imazamox and imazapic as directed by the herbicide labels

disking two weeks laterThis was followed by a second broad-cast spray using 22 kg ae haminus1 glyphosate (Accord XRT DowAgroSciences Indianapolis INUSA) onMarch 25 2009 anddisking on April 7th to provide a bare soil surface optimumto preemergent herbicide performance Sixteen-week-old(from cutting) container-grown rooted stem cuttings of twoEucalyptus urograndis transgenic clonal lines (Frost TolerantEucalyptus (FTE) ArborGen Summerville SC USA) werehand-planted on April 14th 2009 at 24m (between rows) by15m (between trees within rows) spacing (2777 trees haminus1)The two lines were from the same base clone and the sameinserted gene set Each line resulted from an independenttransformation event and as the location of the insertion israndom the effects can be random Of the hundreds of linestested by ArborGen these two lines provided the best coldtolerance growth rate and rooting potential (personal com-munication William Hammond ArborGen February 2012)

23 Experimental Design Five herbicides were chosen fortheir potential to provide selective weed control in eucalyptusplantations and were compared at two application timingspreemergence of weeds (PRE) or post emergence of weeds(POST) and at two rates low or high (Table 1) Sulfometuronmethyl (hereafter referred to as sulfometuron) was alsoapplied at a third rate medium because preliminary testingsuggested eucalyptus tolerance to this herbicide [21] butrate response has been variable in operational experienceRepeated glyphosate applications and a nontreated controlwere used as experimental controls representing two extremeweed control levels near-complete control and no controlrespectively A total of 24 weed control treatments were testedon ten-tree row treatment plots (whole plots) 168m longand 18m wide with the narrow dimension centered on treerows Herbicide type herbicide rate and application timingmain effects were tested in a randomized complete block

design with four replications Five rooted stem cuttings ofeach clone were randomly assigned to half of each whole plotutilizing a split plot design to test for differences between thegenetic lines Treatment plots were separated by 06m widenontreated buffers

24 Treatment Application Preemergent herbicide treat-ments were applied on April 29 2009 and POST herbicidetreatments were applied on May 30 2009 using a CO

2

pressurized backpack research sprayer equipped with a four-nozzle boom fitted with 8002 VS flat fan nozzles (SprayingSystems Wheaton IL USA) 46 cm apart providing a 18meffective swath width A 48 kmhrminus1 ground speed was main-tained using a metronome to adjust walking pace The regu-lator was set to 172 kPa to produce 1900mLminminus1 throughall four nozzles on the boom thus providing 130 L haminus1total spray solution For POST applications spray solutionsof imazamox and imazapic contained 025 (vv) nonionicsurfactant (Induce Helena Chemical Company ColliervilleTN USA) as directed by the labels [16] To maintain nearcomplete weed control an aqueous solution of 2 glyphosateisopropylamine salt (4Accord XRT) was applied as neededas a careful directed spray to avoid contact to eucalyptusfoliage using a backpack sprayer equipped with a hoodedsingle flat fan nozzle During glyphosate applications euca-lyptus trees were additionally protected with polyethyleneshields All glyphosate spraying was done during absolutecalm conditions in the early morning hours to avoid any driftto eucalyptus foliage

25 Measurements

251 Weed Control At 30 60 and 90 days after treatment(DAT) ocular estimates of percent ground cover for bareground (area free of live vegetation) forbs (other than vines)


grasses sedges and vines were made by two experiencedevaluators working together Cover was estimated in four 1by 1m sampling plots per treatment plot (two sampling plotsper clone split plot) centered between seedlings on the rowThe percent ground cover was estimated independently foreach group such that total ground cover may have exceeded100 where groups had overlapping cover Percent cover wasrecorded to the nearest 5 percent for values between 10 and90 cover and to the nearest 1 percent for 0 to 10 and 90 to100 cover The dominant weed species comprising 10 ormore of the total cover in a sampling plot were recorded inthe nontreated control

252 Eucalyptus Injury Symptoms and Growth Eucalyptusinjury was assessed at 30 60 and 90 DAT Each tree wasassigned a symptom severity index (SSI) of 0 to 4 (0 =none 1 = slight 2 = moderate 3 = severe and 4 = extreme)for each injury symptom which included foliar chlorosisfoliar necrosis defoliation fasciculation (multiple buds atstem apices and branch meristems) lateral shoot diebackand leader dieback The percentage of trees with no or onlyminor symptoms was determined at each assessment dateFor this classification slight symptoms of foliar chlorosisfoliar necrosis or defoliationwere consideredminor whereasany symptoms of fasciculation lateral shoot dieback orleader dieback were not regarded as minor Eucalyptus treeswere measured for diameter at 5 cm above ground (GLD

5

)to the nearest 01mm and for total live height (119867) to thenearest 01 cm at planting and at approximately 24 weeks afterplanting on September 29th 2009 Stem volume index wascalculated as GLD

5

2

times 119867

26 Data Analysis Statistical analyses were performed withSAS 92 software [24] Analysis of variance (ANOVA) oranalysis of covariance (ANCOVA) was conducted usingmixed models (Proc Mixed) with blocks treated as randomeffects [25] ANOVAwas conducted for percent ground cover(bare ground forbs grasses sedges and vines) percent treesurvival percentage of treeswith no or onlyminor symptomsandmean severity index for each injury symptom ANCOVAwas conducted for tree stem volume index using the initialstem volume index as a covariate The arcsin square roottransformationwas used for analyses of variables expressed asa percentage and for stem volume index analyses the naturallogarithm of (119883 + 1) transformation where 119883 is the stemvolume index value was used to meet assumptions of nor-mality and homogeneity of variance The backtransformedLS-means are reported The critical level of significance foranalysis of variance and LS-mean comparisons was 120572 = 005Fisherrsquos protected LSD test was used to compare LS-meansThe complete weed control treatment was not included inLS-mean comparisons of percent bare ground or cover fordifferent vegetation groups as multiple applications weremade with the intent to provide near complete weed controland the efficacy of other herbicides was of primary interest

Two analyses were performed for each dependent vari-able The first was a 4-way factorial analysis of a balanceddesign excluding the high sulfometuron rate the nontreated

control and the complete weed control treatment to eval-uate the significance of herbicide type application timingherbicide rate and E urograndis clone (fixed main effects)and their interactions The second full analysis includedall treatments tested Orthogonal contrasts were used totest for the significance of planned comparisons amongthese treatments such as differences among PRE or amongPOST treatments or the significance of herbicide rate andapplication timing effects for individual herbicides

3 Results and Discussion

31 Weed Species Composition Numerous graminoid andforb species were present but only a few were predominantGrasses were the dominant weed group throughout the studyThe most common grass species were large crabgrass [Dig-itaria sanguinalis (L) Scop] southern crabgrass [Digitariaciliaris (Retz) Koel] southern sandspur (Cenchrus echinatusL) and Texas panicum (Panicum texanum Buckl) Sedgeswere less abundant as a group with yellow nutsedge (Cyperusesculentus L) beingmost commonAmong forbs carpetweed(Mollugo verticillata L) was the most prevalent during thefirst evaluation Vente conmigo (Croton glandulosus L varseptentrionalisMull Arg) became the dominant forb speciesas the growing season progressed and common ragweed(Ambrosia artemisiifolia L) cover increased substantiallyduring the study Vine cover was patchy with smallflowermorningglory [Jacquemontia tamnifolia (L) Griseb] mostfrequently recorded and some occurrence of maypop (Pas-siflora incarnata L)

32Weed Control The4-way ANOVA showed no significantE urograndis clone effects for any ground cover variable atany evaluation date (ANOVA not shown) Therefore weedcontrol responses for the two clones combined are presentedand discussed

321 Bare Ground Percent bare ground was significantlyaffected by herbicide type and application timing at allevaluation dates and by herbicide rate at 30 DAT and 60DATWhen compared separately for each herbicide percent bareground was greater for PRE than POST application timingfor all herbicides at 30 DAT and for flumioxazin imazapicand sulfometuron at 60 DAT (contrast results not shown) At90DAT PRE oxyfluorfen resulted in less percent bare groundthan the POST timing Application timing had no effect forother herbicides at 90 DAT

All PRE herbicide treatments resulted in greater percentbare ground than the nontreated control at 30 DAT (Table 2)Bare ground was 80 or more at 30 DAT for all treatmentsexcept the low rates of flumioxazin imazamox and oxyflu-orfen At 60 DAT high sulfometuron and both imazapicrates resulted 77 to 84 bare ground compared to 19 forthe nontreated control Percent bare ground continued todecline for all PRE treatments but at 90DAT some treatmentsdiffered from the nontreated control including the highflumioxazin rate both rates of imazapic medium and highsulfometuron and the high imazamox rate


Table 2 Prevalence of bare ground 30 60 and 90 days after treatment (DAT) for herbicides applied over newly planted Eucalyptus urograndisrooted cuttings either prior to weed emergence (PRE) or after weed emergence (POST) Treatments were evaluated at the end of the monthindicated for each application timing and periodic assessment

Treatment Bare ground cover ()1

Herbicide Rate (g haminus1) 30 DAT 60 DAT 90 DAT2

Applied PRE weed emergence3

May June JulyFlumioxazin 290 ai 74 e 41 d 21 bndasheFlumioxazin 430 ai 80 de 48 cd 38 aImazamox 140 ae 74 e 38 d 21 bndasheImazamox 280 ae 80 de 55 cd 29 andashcImazapic 140 ae 92 andashc 77 andashc 34 abImazapic 210 ae 94 ab 84 a 37 aOxyfluorfen 1120 ai 57 f 13 e 14 deOxyfluorfen 2240 ai 89 andashd 45 d 14 deSulfometuron 26 ai 84 cndashe 51 cd 17 cndasheSulfometuron 53 ai 86 bndashd 64 bc 26 andashdSulfometuron 105 ai 95 a 81 a 31 andashc

Nontreated control 33 g 19 e 13 eComplete weed control 99 97 92

Applied POST weed emergence3

June July AugustFlumioxazin 290 ai 25 fndashi 30 bc 29Flumioxazin 430 ai 27 fndashh 31 bc 28Imazamox4 140 ae 40 de 34 bc 38Imazamox4 280 ae 57 andashc 44 ab 38Imazapic4 140 ae 53 bndashd 43 ab 39Imazapic4 210 ae 70 a 54 a 42Oxyfluorfen 1120 ai 17 hi 27 bc 23Oxyfluorfen 2240 ai 22 gndashi 27 bc 28Sulfometuron 26 ai 43 cndashe 28 bc 33Sulfometuron 53 ai 36 ef 26 cd 28Sulfometuron 105 ai 58 ab 38 andashc 34

Nontreated control 15 i 13 d 21Complete weed control 98 92 95

1LS-means within a column followed by the same letter for PRE or POST applications are not significantly different at 120572 = 005 using Fisherrsquos protectedLSD Means are for the two E urograndis clones combined since clone effects were not significant LS-means for the complete weed control treatment werenot included in LSD comparisons because this treatment was applied repeatedly to provide as close to 100 bare ground as possible and was intended forcomparisons of eucalyptus growth response to weed control2The effect of treatment was not significant for bare ground cover at 90 DAT for POST applications3PRE weed emergence treatments were applied April 29 2009 POST weed emergence treatments were applied May 30 2009 Seedlings were planted April 1420094A nonionic surfactant was added at 025 (vv) for POST applications of imazamox and imazapic as directed by herbicide labels

All POST herbicide treatments had greater percent bareground than the nontreated control at 30 DAT except bothrates of oxyfluorfen and the low flumioxazin rate At 60DAT all treatments resulted in greater bare ground than thenontreated control with the exception of the medium sul-fometuron rateNo significant differences amongPOST treat-ments were observed at 90 DAT

322 Grasses Percent grass cover was significantly affectedby herbicide type andherbicide rate at all evaluation dates andby application timing at 30 and 60DAT (ANOVAnot shown)

Comparing the effect of application timing for individualherbicides percent grass coverwas significantly less followingPRE application thanPOSTapplication for all herbicides at 30DAT and for all herbicides except low oxyfluorfen at 60 DATAt 90 DAT PRE oxyfluorfen resulted in greater percent grasscover than POST

All PRE treatments except low oxyfluorfen resulted insignificantly less grass cover than the nontreated control at30 DAT (Table 3)Themost effective and longest lasting grasscontrol was achieved with medium and high sulfometuronand with both imazapic rates Resulting grass cover at


Table 3 Prevalence of ground cover by vegetation groups 30 60 and 90 days after treatment (DAT) for herbicides applied over newly plantedEucalyptus urograndis rooted cuttings either prior to weed emergence (PRE) or after weed emergence (POST) Treatments were evaluated atthe end of the month indicated for each application timing and periodic assessment

Treatment Ground cover ()1

Herbicide Rate 30 DAT 60 DAT 90 DAT(g haminus1) Grasses Sedges2 Forbs Vines Grasses Sedges Forbs Vines Grasses Sedges Forbs Vines2


May June JulyFlumioxazin 290 ai 17 c 9 0 a 0 a 52 ef 9 dndashf 0 a 0 a 76 e 5 dndashe 0 a 0 abFlumioxazin 430 ai 14 c 6 0 a 0 a 49 ef 5 andashd 0 a 0 ab 59 cndashe 3 bndashd 0 a 0 andashcImazamox 140 ae 3 ab 6 17 e 0 a 36 cndashe 14 f 12 cd 1 andashc 44 bc 8 e 21 cd 2 bndasheImazamox 210 ae 2 ab 7 12 de 0 a 17 bc 11 ef 19 cndashe 0 ab 34 andashc 6 dndashe 29 de 0 andashdImazapic 140 ae 1 ab 3 3 c 0 a 6 ab 2 ab 13 cndashe 0 a 27 ab 1 ab 36 de 0 aImazapic 280 ae 0 a 3 3 c 0 a 3 a 2 a 11 c 0 a 20 a 1 a 38 de 0 aOxyfluorfen 1120 ai 34 d 6 1 andashc 2 b 75 g 6 andashe 2 ab 3 d 81 e 3 bndashd 2 ab 9 fgOxyfluorfen 2240 ai 5 b 6 0 ab 0 a 42 dndashf 12 ef 1 a 1 bndashd 80 e 4 cndashe 1 ab 4 dndashfSulfometuron 26 ai 2 ab 4 10 de 0 a 16 b 8 cndashf 24 e 2 cd 47 bndashd 5 dndashe 30 de 4 endashgSulfometuron 53 ai 0 ab 4 9 d 0 a 5 ab 6 bndashe 23 de 0 andashc 25 ab 5 dndashe 37 de 3 cndashfSulfometuron 105 ai 0 a 2 2 bc 0 a 3 a 3 andashc 12 cndashe 0 andashc 29 ab 4 cndashe 32 de 3 cndashf

Nontreated control 37 d 7 17 e 8 c 61 fg 7 bndashe 9 bc 8 e 72 de 2 andashc 8 bc 10 gComplete weed control 0 0 0 0 0 1 1 1 1 0 0 6


June July AugustFlumioxazin 290 ai 71 f 4 1 a 3 bc 68 f 2 a 1 a 4 bc 66 de 1 a 2 a 3Flumioxazin 430 ai 70 f 3 2 a 3 b 66 f 1 a 2 andashc 1 ab 65 de 0 a 2 a 1Imazamox4 140 ae 53 de 4 7 bc 0 a 54 cndashf 5 ab 9 bndashe 1 a 47 cndashe 1 a 12 andashc 1Imazamox4 210 ae 32 bc 7 7 bc 0 a 37 bndashd 9 b 9 cndashf 2 ab 42 bndashd 7 c 10 andashc 2Imazapic4 140 ae 38 bndashd 4 7 bc 0 a 35 bc 1 a 20 fndashh 0 a 34 bc 0 a 27 cndashe 1Imazapic4 280 ae 17 a 6 10 c 0 a 10 a 1 a 34 h 0 a 11 a 1 a 46 e 1Oxyfluorfen 1120 ai 74 f 6 3 ab 8 de 57 dndashf 3 a 3 andashc 11 e 62 de 0 a 7 ab 7Oxyfluorfen 2240 ai 66 ef 5 3 ab 8 de 61 ef 3 a 2 ab 9 cndashe 67 e 1 a 2 a 4Sulfometuron 26 ai 33 bc 7 12 c 10 e 45 cndashe 5 ab 15 dndashf 10 de 47 cndashe 4 bc 14 andashc 5Sulfometuron 53 ai 47 cd 5 11 c 5 cd 54 cndashf 2 a 19 endashg 6 cndashe 51 cndashe 1 a 19 bndashd 4Sulfometuron 105 ai 27 ab 4 13 c 3 bc 23 ab 3 a 32 gh 5 cd 21 ab 1 ab 40 de 3

Nontreated control 65 ef 5 10 c 11 e 72 f 2 a 8 bndashd 10 de 61 de 1 a 16 bc 6Complete weed control 0 0 1 0 1 0 0 6 0 0 0 41LS-means within a column followed by the same letter for PRE or POST applications are not significantly different at 120572 = 005 using Fisherrsquos protectedLSD Means are for the two E urograndis clones combined since clone effects were not significant LS-means for the complete weed control treatment werenot included in LSD comparisons because this treatment was applied repeatedly to provide as close to 100 bare ground as possible and was intended forcomparisons of eucalyptus growth response to weed control2The effect of treatment was not significant for sedge cover at 30 DAT for PRE or POST applications and for vine cover at 90 DAT for POST applications3PRE weed emergence treatments were applied April 29 2009 POST weed emergence treatments were applied May 30 2009 Seedlings were planted April 1420094A nonionic surfactant was added at 025 (vv) for POST applications of imazapic and imazamox as directed by herbicide label

the various evaluation dates for these treatments ranged from0 to 1 3 to 6 and 20 to 29 at 30 60 and 90 DAT respec-tively compared to 37 61 and 72 respectively for thenontreated control Both rates of imazamox were also effec-tive with 2 to 3 grass cover at 30 DAT and significantlyless grass cover than the nontreated control at all assessmentsFlumioxazin and high oxyfluorfen had less grass cover thanthe nontreated control at 30 DAT but did not control grassesat later assessments

Similar to results observed for PRE treatments amongPOST treatments high imazapic and high sulfometuron ratesprovided the longest lasting and greatest degree of grass

control resulting in 82 and 66 reduction in grass coverrespectively as compared to the nontreated control at 90DATThe low imazapic rate was also effective for postemergencecontrol of grasses with 44 reduction in cover at 90 DATFlumioxazin oxyfluorfen and the low imazamox rate werenot effective for postemergent grass control and did not differfrom the nontreated control at any assessment

323 Sedges Sedge cover was not affected by any factor at30 DAT but was significantly affected by herbicide type andapplication timing at 60 and 90 DAT None of the herbicidetreatments resulted in less sedge cover than the nontreated


control at any evaluation except for the 60 DAT assessmentof PRE imazapic at the high rate (Table 3) Imazapic is widelyused to provide selective nutsedge control in peanut [26]and woody and herbaceous landscape plants [27] Althoughsedge cover was generally low (0 to 14) there were caseswhere PRE applications of imazamox and sulfometuron orPOST imazamox had greater sedge cover than the nontreatedcontrol suggesting that sedgesmay have responded favorablyto the control of other vegetation grasses in particular

324 Forbs When applied PRE both rates of flumioxazinhad no forb cover at any assessment less than the 8 to 17cover observed in the nontreated control (Table 3) Flum-ioxazin treatments applied POST had 1 to 2 forb coverat all assessments less than the 8 to 16 forb cover in thenontreated control with the exception of the high rate at60 DAT Both rates of oxyfluorfen applied PRE resultedin 2 or less forb cover at each assessment although notdifferent from the nontreated control with the low rate at 60DAT and both rates at 90 DAT Oxyfluorfen applied POSThad 3 or less forb cover up to 90 DAT at the high rateand up to 60 DAT at the low rate although not differentfrom the nontreated control for both rates at 60 DAT orfor the low rate at 90 DAT The only other treatments thatresulted in less forb cover than the nontreated control werePRE applied imazapic at both rates and the medium andhigh sulfometuron rates at 30 DAT Herbicide treatmentswhich effectively controlled grasses generally had more forbcover Forb covers greater than the nontreated control wereobserved at 60 DAT for PRE applications of low andmediumsulfometuron and at 90 DAT following all sulfometuronboth imazapic and high imazamox rates Also POST appliedimazapic and sulfometuron had greater forb cover than thenontreated control at 60 DAT for both imazapic rates andmedium and high sulfometuron and at 90 DAT for the highrates of both herbicides

325 Vines All PRE applied herbicides had less vine coverthan observed in the nontreated control (8 to 10 cover) atall evaluation dates except for the low oxyfluorfen and lowsulfometuron rates at 90 DAT (Table 3) POST applicationsof oxyfluorfen and sulfometuron also showed poor vinecontrol with cover not different from the nontreated controlexcept for the medium and high sulfometuron rates at 30DAT Treatment effects for vine cover at 90 DAT were notsignificant for POST application timing

326 Overall Weed Control Efficacy All PRE treatmentsprovided effective weed control but persistent control wasobserved only for high flumioxazin low and high imazapicmedium and high sulfometuron and the high imazamox ratePostemergence treatments were applied when weed coverin the nontreated control averaged 67 Herbicides provid-ing the best overall postemergence weed control includedimazapic imazamox and sulfometuron which all showeda positive herbicide rate response in periodic measures ofpercent bare ground These results are consistent withreported effectiveness in controlling established weeds using

imazapic and imazamox [28] and sulfometuron efficacy incontrolling emerged weeds at an early stage of growth [29]Postemergence applications of flumioxazin and oxyfluorfenwere far less effective in controlling weeds than PRE treat-ments which is consistent with label directions that statethese herbicides are most effective when applied to bare soilUnlike results observed for PRE treatments by the 90 DATassessment none of the POST applied herbicides differedfrom the nontreated control as measured by bare ground

The herbicides tested are more effective for control ofannual plants than perennials [7] Imazapic and sulfome-turon controlled annual grasses with both PRE and POSTapplications The high rate of imazapic controlled sedge withPRE application timing but other herbicides resulting in ahigh degree of grass control (imazamox sulfometuron) hadgreater sedge cover than the nontreated control Flumioxazinand oxyfluorfen were highly effective for forb control whenapplied PRE but did not control annual grasses Climbingvines are damaging in newly established eucalyptus planta-tions and some species particularly morningglory are notcontrolledwith selective herbicides currently available for usein eucalyptus plantations in the USA Vine control was bestwith PRE treatments although POST treatments were alsoeffective except for oxyfluorfen and the low sulfometuronrate Morningglory which was the predominant vine onthis study site and is common on old-field sites in theregion is large-seeded and tends to germinate later thanmany common agricultural weeds such that it is often notcontrolled with herbicides having short residual activity

Blazer et al [14] tested seven herbicides at various rates inLouisianaUSA at an early postemergence application timingand similar stage of eucalyptus growth in E macarthurii andassessed ground cover at 5 10 and 15 weeks after treatmentTheir study included 51 and 101 g haminus1 oxyfluorfen muchlower than the 11 and 22 kg haminus1 rates tested in our studyThey also tested 27 and 66 g haminus1 sulfometuron similar to thelow and medium rates we tested At five weeks after treat-ment they observed 3 to 8 ground cover with oxyfluorfentreatments and 10 to 12 ground cover with sulfometuronwhich were among their most effective treatments Ourresults with sulfometuron are similar but they observedbetter efficacy for much lower rates of oxyfluorfen perhapsbecause only two susceptible annual forbs and one annualgrass were predominant at their study location In their studyno differences in ground cover among herbicide treatmentsand the nontreated control were observed at 10 and 15 weeksafter treatment whereas in our study weed control persistedto 90 DAT for all PRE applied herbicides except oxyfluorfen

We found only one other study testing flumioxazin ineucalyptus plantations In Vicosa Brazil Tiburcio et al [17]compared flumioxazin alone at 75 100 and 125 g haminus1 andcombinations of flumioxazin and isoxaflutole or sulfentra-zone to the standard 960 g haminus1 oxyfluorfen rate (similar toour low rate) at preemergence timing 20 days after planting Egrandis clones They concluded that the highest flumioxazinrate testedwas as effective as the oxyfluorfen standard but thatthe combinations of flumioxazin with the other herbicideswere more effective in controlling weeds than flumioxazin


Table 4 ANOVAANCOVA1119875 values for the percentage of Eucalyptus urograndis trees showing no or minor injury symptoms at 30 60

and 90 days after treatment (DAT) for survival and stem volume index (SVI) at the end of the first growing season and for five herbicidesapplied at two rates and two application timings over newly planted rooted cuttings of two E urograndis clones

Factor

Dependent variablePercentage of trees with no or

minor injury symptoms2 Survival SVI3

30 DAT 60 DAT 90 DATApplication timing (AT)4 lt00001 0240 lt00001 lt00001 lt00001Herbicide (herb)5 lt00001 lt00001 lt00001 lt00001 lt00001Rate6 0080 0047 0294 0947 0364Clone7 0757 0736 0634 0666 0781AT times herb lt00001 0024 0000 lt00001 lt00001AT times rate 0205 0099 0073 0947 0217AT times clone 0426 0495 0816 0666 0178Herb times rate 0592 0102 0872 1000 0134Herb times clone 0743 0898 0943 0944 0963Rate times clone 0620 0626 0855 0482 0495AT times herb times rate 0765 0069 0565 1000 0386AT times herb times clone 0135 0978 0391 0944 0216AT times rate times clone 0514 0405 0666 0482 0931Herb times rate times clone 0818 0394 0469 0738 0841AT times herb times rate times clone 0879 0802 0496 0738 04951ANCOVA was conducted for SVI ANOVA was conducted for the other variables2Slight foliar chlorosis slight foliar necrosis and slight defoliation were considered minor injury symptoms whereas any observed fasciculation lateral shootdieback and leader dieback were not regarded as minor3Stem volume index (SVI) = GLD

5

2

times 119867 GLD5 = outside bark stem diameter 5 cm above the ground119867 = live stem height4PRE weed emergence or POST weed emergence5Flumioxazin imazamox imazapic oxyfluorfen or sulfometuron methyl6Rate = low or high relative rate7Two ArborGen proprietary transgenetic FTE (frost tolerant eucalyptus) clones

alone In our study weed control with PRE flumioxazin dem-onstrated a positive rate response to 430 g haminus1 with no con-cerns regarding eucalyptus phytotoxicity To our knowledgeno published studies other than a preliminary researchreport from our research center [21] have examined imaz-amox or imazapic applications for selective weed control ineucalyptus plantings

33 Eucalyptus Injury Symptoms and Growth In the fullANOVA there were no significant differences between thetwo eucalyptus clones for the various injury symptom severityindices (SSI ANOVA not shown) percentage of trees withno or minor injury symptoms tree survival or stem volumeindex (Table 4) so treatment means for the two clonescombined were compared

331 Eucalyptus Injury Symptoms Themost significant phy-totoxicity was observed with PRE and POST imazapic POSTimazamox POST sulfometuron and PRE sulfometuron atthe high rate With the exception of imazapic herbicideinjury symptoms declined with time as trees recovered Themost pronounced and consequential injury symptoms werefasciculation leader and lateral shot dieback and defoliation

Imazapic caused severe tree injury symptoms at bothapplication rates and timings When applied PRE it causeddefoliation fasciculation and leader dieback (results notshown) Compared to the other herbicide treatments andnontreated control imazapic resulted in greater severityindex for fasciculation at all evaluation times (11 to 37) andfor defoliation and leader dieback at 30 DAT (05 to 06 and08 to 10 resp) and at 60DAT (05 to 06 and 08 to 09 resp)At 90 DAT defoliation was no longer observed for imazapictreatments but leader dieback was observed for the high rate(SSI 03) For PRE sulfometuron at the high rate elevatedseverity indices were observed at 30DAT for defoliation (03)fasciculation (08) and leader dieback (03) compared to SSI0 for all symptoms for the nontreated control

Imazapic resulted in the most severe injury symptomsamong POST herbicides as well At 30 DAT all imazapic-treated trees exhibited extreme lateral shoot dieback (themaximum SSI of 4) This index diminished with time toSSI 02 to 03 at 90 DAT but was greater than the otherPOST herbicide treatments and nontreated control (SSI 0)through 90 DAT POST imazapic also resulted in greaterleader dieback index than the nontreated control (SSI 0) at30 DAT (SSI 10 both rates) and at 60 DAT (SSI 03 lowrate only) Fasciculation SSI at 60 DAT was 23 and 16 with


Table 5 Percentage of Eucalyptus urograndis trees with no or minor injury symptoms at 30 60 and 90 days after treatment (DAT) forherbicides applied over newly planted rooted cuttings either prior to weed emergence (PRE) or after weed emergence (POST) Treatmentswere evaluated at the end of the month indicated for each application timing and periodic assessment

Treatment Percentage of trees with no or minor injury symptoms12

Herbicide Rate (g haminus1) 30 DAT 60 DAT 90 DATApplied PRE weed emergence3

May June JulyFlumioxazin 290 ai 100 a 100 a 95 andashcFlumioxazin 430 ai 100 a 100 a 88 bcImazamox 140 ae 97 a 100 a 78 cImazamox 280 ae 99 a 100 a 92 andashcImazapic 140 ae 0 c 0 b 0 dImazapic 210 ae 0 c 0 b 1 dOxyfluorfen 1120 ai 100 a 99 a 82 bcOxyfluorfen 2240 ai 100 a 99 a 93 andashcSulfometuron 26 ai 99 a 99 a 81 bcSulfometuron 53 ai 96 a 100 a 99 abSulfometuron 105 ai 53 b 99 a 100 a

Nontreated control 100 a 100 a 96 andashcComplete weed control 99 a 100 a 99 ab


June July AugustFlumioxazin 290 ai 99 a 99 ab 99 aFlumioxazin 430 ai 99 a 100 a 100 aImazamox4 140 ae 6 cd 100 a 100 aImazamox4 280 ae 0 d 100 a 100 aImazapic4 140 ae 0 d 0 d 73 bImazapic4 210 ae 0 d 27 c 56 bOxyfluorfen 1120 ai 100 a 100 a 100 aOxyfluorfen 2240 ai 99 a 100 a 100 aSulfometuron 26 ai 29 b 98 ab 100 aSulfometuron 53 ai 10 bc 99 ab 97 aSulfometuron 105 ai 8 c 86 b 100 a

Nontreated control 100 a 100 a 100 aComplete weed control 100 a 100 a 100 a

1Slight foliar chlorosis slight foliar necrosis and slight defoliation (slight = symptom severity index 1 in a 0ndash4 scale) were considered minor injury symptomswhereas any observed fasciculation lateral shoot dieback or leader dieback were not regarded as minor2LS-means within a column followed by the same letter for PRE or POST applications are not significantly different using Fisherrsquos protected LSD at 120572 = 05Means are for the two E urograndis clones combined since clone effects were not significant3PRE weed emergence treatments were applied April 29 2009 POST weed emergence treatments were applied May 30 2009 Seedlings were planted April 1420094A nonionic surfactant at 025 (vv) was added for POST applications of imazapic and imazamox as directed by the herbicide label

low and high rates of imazapic respectively greater than thenontreated control (SSI 0) All rates of POST imazamox andsulfometuron resulted in increased lateral shoot dieback at 30DAT (SSI 18 to 29 and 13 to 19 resp) as compared to thenontreated control (SSI 0) but trees recovered by 60 DAT(Table 5) Additionally trees treated with low and mediumsulfometuron exhibited some defoliation at 90 DAT (SSI 07)

332 Eucalyptus Condition Preemergence applications ofboth the low and high rates of flumioxazin imazamox and

oxyfluorfen as well as the low and medium rates of sul-fometuron resulted in negligible phytotoxicity (Table 5) Thepercentage of trees with no or minor symptoms at 30 and60 DAT was 96 or greater for these treatments with nophytotoxicity observed with flumioxazin At the high sul-fometuron rate phytotoxicity was observed at 30 DAT butby 60 DAT 99 of trees had no or minor injury symptomsAt 90 DAT the number of trees with no or minor symptomsdeclined for oxyfluorfen flumioxazin and imazamox as sometrees exhibited chlorosis and necrosis probably caused by


Table 6 Survival and stem volume index of Eucalyptus urograndis trees at the end of the first growing season for preemergence (PRE) orpostemergence (POST) applications of various herbicides in comparison to a nontreated control and complete weed control obtained withrepeated foliar sprays of glyphosate herbicide directed carefully to weeds

Treatment Rate (g haminus1)Survival1 Stem volume index12

() (cm3)PRE POST PRE POST

Flumioxazin 290 ai 100 a 100 a 157 bc 46 cndasheFlumioxazin 430 ai 100 a 100 a 226 bc 55 cndasheImazamox3 140 ae 100 a 100 a 200 bc 315 bImazamox3 280 ae 100 a 100 a 91 cd 116 cImazapic3 140 ae 64 b 100 a 41 de 55 cndasheImazapic3 210 ae 63 b 100 a 22 e 56 cndasheOxyfluorfen 1120 ai 100 a 100 a 173 bc 91 cdOxyfluorfen 2240 ai 100 a 100 a 403 b 65 cndasheSulfometuron 26 ai 100 a 100 a 175 bc 47 cndasheSulfometuron 53 ai 100 a 100 a 276 b 26 eSulfometuron 105 ai 100 a 100 a 348 b 65 cndashe

Nontreated control 100 a 100 a 42 de 42 deComplete weed control 100 a 100 a 2665 a 2665 a

1LS-means within a column followed by the same letter are not significantly different at 120572 = 005 using Fisherrsquos protected LSD Means are for the two Eurograndis clones combined since clone effects were not significant2Stem volume index (SVI) = GLD

5

2

times 119867 GLD5 = outside bark stem diameter 5 cm above the ground119867 = live stem height3A nonionic surfactant at 025 (vv) was added for POST applications of imazapic and imazamox as directed by the herbicide label

competition from grasses not controlled by these treatmentsTrees in treatments giving better grass control the mediumand high rates of sulfometuron did not show this declineSignificant injury occurredwith PRE applications of imazapicat the rates tested with essentially all trees showing injurywithout recovery At the 90 DAT assessment only imazapicdiffered from the nontreated control with practically nosymptom-free trees

Among POST treatments flumioxazin and oxyfluorfenresulted in negligible phytotoxicity to eucalyptus trees with99 to 100 showing no or minor injury symptoms at allassessments (Table 5) Injury largely characterized by lateralshoot dieback increased with increasing sulfometuron rateat 30 DAT At that assessment 8 to 29 of trees treatedwith sulfometuron had no or minor symptoms but nearly alltrees recovered by 90 DAT In general recovery from initialphytotoxic symptoms was more pronounced following POSTapplications than for PRE treatments This was likely dueto better resilience of the more established trees in POSTtreatments applied one month later than PRE treatmentsThis effect was most pronounced for POST imazamox whichhad 0 to 6 of trees with no or minor injury at 30 DAT andfull recovery to 100 of trees in this condition at 60 and 90DAT As observed with PRE applications imazapic resultedin the greatest and longest lasting phytotoxicity among POSTtreatments However unlike PRE treatment responses whenimazapic was applied POST to more established transplants56 to 73 of the trees recovered to show no or minorsymptoms at 90DATThegreater tolerance observed formoreestablished trees is consistent with a supplemental imazapicproduct label for use in sweetgum (Liquidambar styracifluaL) fiber farms in the USA [30] which recommends that

applications after planting occur when trees have not brokendormancy or at any time after 60 d from full leaf expansionFor POST treatments nearly all trees had no or minorsymptoms at the 90 DAT assessment except for imazapic

333 Eucalyptus Survival and Stem Volume Index Euca-lyptus survival was 100 for all treatments with exceptionof PRE imazapic treatments which resulted in 63 to 64survival (Table 6)The full ANOVAdid not show a significantherbicide rate effect on stem volume index (SVI) but theeffects of herbicide type application timing and the inter-action between herbicide type and timing were significant(Table 4) Contrasts (results not shown) to examine rateeffects on SVI for individual herbicides identified a significantrate effect (119875 = 00105) for imazamoxThe low imazamox rateresulted in 220 (PRE) or 272 (POST) greater stem volumeindex than the high rate suggesting that future studies shouldexamine rates less than 280 g ae haminus1 Application timing wassignificant for flumioxazin oxyfluorfen and sulfometuronwith PRE applications resulting in greater SVI than POSTtreatments for each of these herbicides regardless of the rateStem volume index was not affected by imazapic rate orapplication timing

All PRE treatments except both rates of imazapic andthe high imazamox rate resulted in trees with significantlylarger stem volume index than the nontreated control Thehigh rate of oxyfluorfen gave the greatest stem volume indexamong PRE treatments although not significantly differentfrom other treatments except both rates of imazapic and thehigh imazamox rate Among POST treatments both rates ofimazamox were the only treatments with greater SVI thanthe nontreated control The low rate of imazamox resulted in


the largest stem volume index among POST treatments andwas significantly greater than all treatments except completeweed control

The complete weed control treatment provided an oppor-tunity to examine eucalyptus growth potential in the absenceof competition and with minimal direct negative herbicideeffects Complete weed control resulted in stem volume indexmore than sixfold greater than the best herbicide treatmentapplied over trees the high rate of oxyfluorfen applied PREComplete weed control also resulted in eucalyptus volumeindex more than sixtyfold greater than the nontreated con-trol demonstrating the impact of competing vegetation onthe growth of young trees In a similar eucalyptus estab-lishment study in Louisiana Blazer et al [14] compared tenherbicide treatments to a nontreated control and directed 5glyphosate applications made three times during the growingseason Periodic directed glyphosate applications resulted ina 30 reduction in one year height growth as compared to thenontreated control indicating the potential for injury withthis approachHowever in a subsequent study they comparedvarious sulfometuron rates and nontreated control to thesame regime of periodic directed glyphosate applications andobserved 220 greater one year height growth with directedglyphosate sprays as compared to the nontreated controlperhaps demonstrating the need for careful application toavoid eucalyptus foliage

4 Summary and Conclusions

Our results confirm sensitivity of newly planted eucalyptusto competing vegetation and underscore the importance ofthe balance between effective vegetation control and herbi-cide tolerance Repeated glyphosate applications can provideeffective weed control and enhance eucalyptus growth but arecost-intensive and can result in severe injury or mortality iftrees are not adequately protected This study demonstratedthat a single application of one of several selective herbicidesover newly planted rooted eucalyptus cuttings may enhancetheir growth Repeated applications of selective herbicidescould possibly further enhance growth as suggested by thelarge growth response to complete weed control In generalPRE applications of the herbicides tested were more effectivethan POST applications and also provided weed controlduring the critical period of tree establishment

Our results confirm that oxyfluorfen is effective for selec-tive control of forbs in newly established eucalyptus plantingsat PRE application timing We have shown that flumioxazinis also effective for forb control at PRE application timingand that both oxyfluorfen and flumioxazin may be applied atthe rates tested for selective weed control in newly plantedeucalyptus during active growth We have confirmed thatsulfometuron is most effective for selective control of annualgrasses and forbs in newly planted eucalyptus at PRE timingand have refined selective herbicide rate response Althoughtemporary phytotoxicity was observed using the high sul-fometuron rate (105 g haminus1) this treatment was among thebest PRE treatments in stem volume index response Ourstudy identified two new imidazolinone herbicides for selec-tive weed control in eucalyptus plantings Imazamox showed

good selectivity and broad spectrum weed control at bothapplication timings and generally resulted in the best selectiveweed control among POST treatments In spite of temporaryphytotoxicity both imazamox rates were the only POSTtreatments resulting in greater stem volume index than thenontreated control and the volume response to the low(140 g ae haminus1) imazamox ratewas greater than all other POSTtreatments Lower imazapic rates applications at a moreadvanced stage of growth and directed sprays should betested for eucalyptus tolerance as this herbicide was mostefficacious for weed control and shows promise for selectiveuse in established stands

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors wish to acknowledge the assistance of Dr JeffWright ArborGen in planning this study as well as in-kind and financial support fromArborGen Summerville SCDr Dwight Lauer Silvic Analytic Charlotte NC providedhelpful guidance in data analyses and interpretation SethWright and Luke Wright are acknowledged for their carefulconduct of the field research

References

[1] J Davidson ldquoEcological aspects of Eucalyptus plantationsrdquo inProceedings of Regional Expert Consultation on Eucalyptus vol1 FAO Corporate Document Repository 1993

[2] D L Rockwood ldquoHistory and status of Eucalyptus improve-ment in Floridardquo International Journal of Forestry Research vol2012 Article ID 607879 10 pages 2012

[3] R N Pires F C M Pereira M P Nepomuceno and P L C AAlves ldquoEffects of the simulated drift of ripeners on Eucalyptusurograndisrdquo Journal of Agricultural Science vol 5 no 12 pp 78ndash86 2013

[4] D Dougherty and J Wright ldquoSilviculture and economic evalu-ation of eucalypt plantations in the Southern USrdquo BioResourcesvol 7 no 2 pp 1994ndash2001 2012

[5] R C Kellison R Lea and PMarsh ldquoIntroduction of Eucalyptusspp into the United States with Special Emphasis on the South-ern United Statesrdquo International Journal of Forestry Researchvol 2013 Article ID 189393 9 pages 2013

[6] Sappi ldquoMaintenancerdquo in Silviculture chapter 9 pp 56ndash64South African Pulp and Paper Industries 2014 httpwwwsappicomregionssaSappiSouthernAfricaSappi20ForestsTree20Farming20GuidelinesPart202 Silviculture Chap-ter209 Maintenancepdf

[7] A Osiecka and P J Minogue ldquoHerbicides for weed control inEucalyptus plantingsrdquo Circular FR-378 University of FloridaCooperative Extension Service 2013 httpedisifasufledufr378

[8] P R Adams C L Beadle N J Mendham and P J SmethurstldquoThe impact of timing and duration of grass control on growthof a young Eucalyptus globulus Labill plantationrdquo New Forestsvol 26 no 2 pp 147ndash165 2003


[9] S K Florentine and J E D Fox ldquoCompetition between Euca-lyptus victrix seedlings and grass speciesrdquo Ecological Researchvol 18 no 1 pp 25ndash39 2003

[10] A M Garau C M Ghersa J H Lemcoff and J J BaranaoldquoWeeds in Eucalyptus globulus subspmaidenii (F Muell) estab-lishment effects of competition on sapling growth and sur-vivorshiprdquo New Forests vol 37 no 3 pp 251ndash264 2009

[11] G Meskimen ldquoFertilizer tablets stimulate eucalyptus in Floridatrialrdquo USDA Forest Service ResearchNote SE-162 USDA ForestService Lehigh Acres Fla USA 1971

[12] A P Schonau R V van Themaat and D I Boden ldquoTheimportance of complete site preparation and fertilising in theestablishment of Eucalyptus grandisrdquo South African ForestryJournal vol 116 no 1 pp 1ndash10 1981

[13] L D Tuffi Santos R M S A Meira F A Ferreira B FSantrsquoAnna-Santos and L R Ferreira ldquoMorphological responsesof different eucalypt clones submitted to glyphosate driftrdquoEnvironmental and Experimental Botany vol 59 no 1 pp 11ndash20 2007

[14] M A Blazer J Johnson E L Taylor and B Osbon ldquoHerbicidesite preparation and release options for eucalyptus planta-tion establishment in the Western Gulfrdquo in Proceedings ofthe 16th Biennial Southern Silvicultural Research ConferenceGeneral Technical Report SRS-156 pp 19ndash23 USDA ForestService Southern Research Station Ashville NC USA 2012httpwwwtreesearchfsfeduspubs40572

[15] D L Shaner EdHerbicide Handbook Weed Science Society ofAmerica Lawrence Kan USA 10th edition 2014

[16] Crop Data Management Systems Labels amp MSDS ldquoClearcastrdquoldquoGoalrdquo ldquoPlateaurdquo ldquoSureGuardrdquo CDMS 2015 httpwwwcdmsnetmanuf

[17] R A S Tiburcio F A Ferreira L R Ferreira M S Machadoand A F L Machado ldquoWeed control and selectivity of flumiox-azin in eucalyptusrdquo Cerne vol 18 no 4 pp 523ndash531 2012

[18] H M Brown ldquoMode of action crop selectivity and soil rela-tions of the sulfonylurea herbicidesrdquo Pesticide Science vol 29no 3 pp 263ndash281 1990

[19] G F Meskimen D L Rockwood and K V Reddy ldquoDevelop-ment of Eucalyptus clones for a summer rainfall environmentwith periodic severe frostsrdquo New Forests vol 1 no 3 pp 197ndash205 1987

[20] M Hinchee W Rottmann L Mullinax et al ldquoShort-rotationwoody crops for bioenergy and biofuels applicationsrdquo In VitroCellularampDevelopmental BiologymdashPlant vol 45 no 6 pp 619ndash629 2009

[21] AOsiecka andP JMinogue ldquoPreliminary results developmentof selective herbicide treatments for establishment of Eucalyp-tus urograndis (FTE) and Eucalyptus benthamii plantationsrdquoResearch Report 2011-01 Institute of Food and AgriculturalSciences North Florida Research and Education Center Uni-versity of Florida Quincy Fla USA 2011

[22] National Oceanic and Atmospheric Administration ldquoMonthlystation normals of temperature precipitation and heating andcooling degree days 1971ndash2000rdquo in Limatography of the UnitedStates No 8108mdashFlorida National Climatic Data CenterNESDISNOAA National Oceanic and Atmospheric Admin-istration Asheville NC USA 2002 httpcdoncdcnoaagovclimatenormalsclim81FLnormpdf

[23] United States Department of Agriculture Natural ResourcesConservation ServiceWeb Soil Survey 2012 httpwebsoilsur-veynrcsusdagov

[24] SAS Institute SASSTAT 92 Userrsquos Guide SAS Institute CaryNC USA 2007

[25] R C Littell G A Milliken W W Stroup R D Wolfinger andO Schabenberger SAS for Mixed Models SAS Institute CaryNC USA 2nd edition 2006

[26] W J Grichar and P R Nester ldquoNutsedge (Cyperus spp)control in peanut (Arachis hypogaea) with AC 263222 andimazethapyrrdquoWeed Technology vol 11 no 4 pp 714ndash719 1997

[27] R T Hurt andWK Vencill ldquoEvaluation of three imidazolinoneherbicides for control of yellow and purple nutsedge in woodyand herbaceous landscape plantsrdquo Journal Environmental Hor-ticulture vol 12 pp 131ndash134 1994

[28] D L Shaner andNMMallipudi ldquoMechanisms of selectivity ofthe imidazolinone herbicidesrdquo inThe Imidazolinone HerbicidesD L Shaner and S LOrsquoConnor Eds chapter 7 pp 91ndash102 CRCPress Boca Raton Fla USA 1991

[29] A M Blair and T D Martin ldquoA review of the activity fate andmode of action of sulfonylurea herbicidesrdquoPesticide Science vol22 no 3 pp 195ndash219 1988

[30] BASF ldquoPlateau supplemental labelingrdquo Tech Rep PE-47061BASF Triangle Park NC USA 1999

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ClimatologyJournal of


sprays to avoid eucalyptus foliage contact Because glyphosatedoes not provide soil residual herbicide activity applicationsprior to planting are not injurious to eucalyptus transplantsConversely applications after planting often reduce growthrates or cause significant injury or mortality because it isdifficult to eliminate drift in operational practice even withdirected sprays In their study of the effect of glyphosate spraydrift to eucalyptus clones Tuffi Santos et al [13] observed aprogression of injury symptoms from leaf chlorosis throughnecrosis to plant death with phytotoxicity positively corre-lated to increasing application rate Multiple applications ofglyphosate are needed through the growing season as newweeds emerge resulting in a significant cost [14] There arealso concerns regarding the development of resistant weedswhen a single herbicide or herbicides with a common modeof action are used particularly with repeated applications andhigh selection pressure

Oxyfluorfen and flumioxazin are selective herbicideswhichmay be applied over newly planted eucalyptus Oxyflu-orfen is effective as a pre- and early postemergence herbicideon small-seeded annual forbs and it suppresses annual grassesbut provides poor control of perennial grasses [15] Oxyflu-orfen is widely used in eucalyptus silviculture but currentproduct labels restrict applications to ldquodormantrdquo trees [16] acondition that may not exist in some climates because euca-lyptus have naked bud habit and are never truly dormant Flu-mioxazin is effective for forb and annual grass control whenapplied preemergence or at a very early stage of weed growth[16] but because of photodegradation this herbicide has shortresidual activity [15] Flumioxazin is labeled for use in ldquofieldgrown deciduous treesrdquo [16] but not specifically for eucalyp-tus plantations In a recent study in Brazil [17] flumioxazinrates ranging from 75 to 125 g active ingredient (ai) haminus1 wereexamined for selective weed control in newly planted Euca-lyptus grandisWHill exMaid clonesThe authors concludedthat flumioxazin is selective to eucalyptus at the highest ratetested but that combinations with other herbicides providedbetter weed control Research is needed to refine applicationrate and timing relative to stage of eucalyptus growth andweed development for both oxyfluorfen and flumioxazin

Sulfometuron methyl (hereafter referred to as sulfome-turon) is a soil residual herbicide providing selective weedcontrol with either pre- or postemergence applications ineucalyptus plantations although best efficacy is obtainedwhen weeds are in an early stage of growth Specific herbicidelabeling for eucalyptus plantations is currently limited [7]Sulfometuron is perhaps most promising as it is a longresidual herbicide and controls a broad spectrum of annualand perennial weeds however seedling injury is a seriousconcern where soil pH exceeds 6This is explained by greatersoil residual activity as degradation by hydrolysis is limitedin alkaline conditions [18] Blazer et al [14] found applica-tions of oxyfluorfen and sulfometuron to reduce competingvegetation and promote Eucalyptus macarthuriiH Dean andMaiden seedling height growth better than directed spraysof glyphosate but emphasized the need for future researchto define sulfometuron rate responses for various vegetationtypes and soils

Eucalyptus afforestation efforts by forest industry in thesouthern US have had limited success because of frost intol-erance [5 19] but there is renewed interest in planting cold-tolerant species hybrids and genetically modified cold hardyplanting stock to meet increasing hardwood fiber demandand to supply potential bioenergymarketsThe hybrid E uro-grandis a cross between E grandis and E urophylla ST Blakehas shown suitability for plantation culture in the southeast-ern US [5] Advanced breeding techniques including geneticmodification are being used to develop cold hardy cultivarssuch as Arborgenrsquos (Summerville South Carolina USA)ldquoFrost Tolerant Eucalyptusrdquo (FTE) E urograndis clones [20]Selective herbicides for FTE clones have not been identified

Preliminary experiments at our research center demon-strated the effectiveness of imazamox and imazapic herbi-cides for selective weed control in newly established eucalyp-tus plantations in north Florida although selectivity differedby herbicide rate application timing and Eucalyptus species[21] These herbicides have the advantage of being effectiveboth before and after weed emergence but provide varyingdegrees of residual weed control [15] This study examinesfour promising herbicides for selective weed control in euca-lyptus flumioxazin imazamox imazapic and sulfometuronrelative to the widely used oxyfluorfen operational standardto refine application rate and timing recommendations forselective weed control in two genetically modified frost-tolerant hybrid lines of Eucalyptus urograndis

Eucalyptus growth response to selective herbicide treat-ments reflects a balance between direct negative effects ofthe herbicide and the benefits of competition control Tobetter examine their selectivity herbicide treatments werecompared to two experimental controls one which was non-treated and one receiving near complete weed control usingcareful directed sprays of glyphosate The complete weedcontrol treatment demonstrates the potential for eucalyptusgrowth in the absence of competition and herbicide phyto-toxicity

2 Materials and Methods

21 Site Description The study site was a fallow agriculturalfield located at the University of Florida North FloridaResearch and Education Center south of the city of Quincyin the lower Coastal Plain region of Florida USA (30∘321015840N84∘351015840W) at an altitude of approximately 70mThe local cli-mate is temperate warm and wet with highest temperaturesin July (mean temperature 271∘C maximum temperature327∘C) lowest temperatures in January (mean tempera-ture 103∘C minimum temperature 40∘C) and 1431mmannual precipitation [22] The soil is a Dothan- (fine-loamykaolinitic and thermic Plinthic Kandiudults) Fuquay (loamykaolinitic and thermicArenic PlinthicKandiudults) complex[23]

22 Site Preparation and Plantation Establishment In Octo-ber 2008 the study site was prepared for planting by applying34 kg acid equivalent (ae) haminus1 glyphosate herbicide (RazorPro Nufarm Burr Ridge IL USA) as a broadcast spray and














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