responding to lawn weed management questions dr. john stier university of wisconsin-madison...
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Responding to Lawn Weed Management Questions
Dr. John StierUniversity of Wisconsin-Madison
Environmental Turfgrass Extension Specialist
Presence of Weeds Usually Presence of Weeds Usually Indicates Underlying ProblemIndicates Underlying Problem
Turfgrasses adapted to the local environment resist weeds best
Good Turf Management
• Mowing– 2-3 inch height: 1/3 Rule– Sharp blades
• Fertility– 3-4 lb N/1000 ft2: Holiday Schedule
• Irrigation• Turf species
– Kentucky bluegrass/perennial ryegrass– Fine fescue: low maintenance, dry shade– Rough or supina bluegrasses for moist
shade
Moss and Moss and AlgaeAlgae
• Low light• Restricted air movement• Poor drainage• Often compounded by poor management
Why do I Have Weeds in My Lawn Again This Year?
• Correct product used?– Age, storage
• Rate?• Timing?
– Rain, growing conditions– Temperature
• Low-restrict absorption/translocation• Warm to mod. high-best
absorption/translocation• V. high-dries on surface prior to absorption
• Turf cover & management
Post-Emergent Post-Emergent Grassy Weed Grassy Weed
ControlControl
• Difficult
• Annuals: crabgrass– MSMA: retail
• Perennials: tall fescue, bentgrass, quackgrass, nimblewill– Glyphosate (Roundup, Kleenup)
Creeping Bentgrass
• Poor quality seed– May take years to
become noticeable– Puffy patch, small-
leaved grass
• Fine stolons easily ripped up
• Spray glyphosate 1 ft past perimeter of patch
Bentgrass patch1 ft
stolons
Pre-Emergent Weed HerbicidesPre-Emergent Weed Herbicides
• Form barrier between soil surface and seed– Irrigation or rainfall
• Prevent seed germination– apply March-April– Used for annual grasses, some broadleaves– Will stop perennial germination
• Examples: pendimethalindithiopyr (some post-emergent)siduron--OK for seeding
Crabgrass and Quackgrass
• Spring and summer• Light green color• Brown after frost• Short, wide leaves• Fine hairs on
leaves/stem• Easy to pull plant
• Perennial• Gray-green color• Longer, narrower
leaves• Few hairs• Auricles• Can’t pull plant• Rhizomes
Post-Emergent Post-Emergent Broadleaf Broadleaf HerbicidesHerbicides
• Apply to visible weeds when actively growing
• Broadleaf weed control: 2,4-D; MCPP; MCPA; dicamba; triclopyr– Sold in combinations (e.g., Weed-B-Gon)– Dicamba is soil mobile, can damage taxus,
junipers, others
Factors Affecting Factors Affecting Herbicide ControlHerbicide Control
• Formulations– Esters
• volatile• readily absorbed• use during cool temps or hard-to-kill weeds
– Salts• less volatile• use during hot temps• less smell
Wild violet
Weed and Feed ProductsWeed and Feed Products
• Herbicide impregnated on fertilizer prill
• Post or pre-emergence
• Post: Stick to leaves?
• Pre: Timing?
“Non-Toxic” Pesticides
• Misnomer: Pesticides intended to be toxic to pests
• EPA regulates toxicity: no significant danger when used properly
• Avoid reliance on non-regulated “biological” or “organic” pesticides– May not work– No toxicity testing!
LD50 and LC50 Measure & Rate Acute Toxicity
• Amount to kill 50% of animals = Lethal Dose to 50% (LD50)
• LC50 = Inhalation Toxicity
• Lower LD or LC50 values = More toxic!
Toxicity of Common Substances
CuSO4 Bordeaux Mixture
Fungicide 11
Caffeine --- --- 192
2,4-D Various Herbicide 375-666
*Aspirin --- --- 1240
*Table salt --- --- 3320
Glyphosate Roundup Herbicide 5800
LD50
Source: Pesticide profiles: Toxicity, environmental impact, & fate. 1997. M.A. Karmin (ed). Lewis Publishers*Source: Applied weed science. 1999. M.A. Ross & C.A. Lembi. Prentice-Hall.
3500
ppm
= 1
0 oz
ai/
180
lb a
dult
EPA: 2,4-D Not Linked to Human Cancer (9 Aug. 2007)
• 300 studies since 1989• "Based on extensive scientific
review of many epidemiology and animal studies, the Agency finds that the weight of the evidence does not support a conclusion that 2,4-D, 2,4-DB and 2,4-DP are likely human carcinogens," according to a notice released by EPA.
Pesticide FatePesticide Applied
(Volatilize)
(Drift)
Photodecomposition
Runoff ?
Plant Uptake & Degradation
Thatch AdsorptionMicrobial decomposition
Soil ChemistryReactions and Decomposition
Leaching?
Corn Gluten Meal
• Accidental discovery
• Research-based!
• Activity– Herbicidal(?)– Fertility (10% N)
Corn Gluten Meal Application
• 12-20 lb/M– Early spring– Late summer
• Irrigate
• Timing critical– Short-lived peptides
Crabgrass Reduction in Field Trials of Corn Gluten Meal on Kentucky Bluegrass
1988 (4 wks pre-) 1991 (1 wk pre-)
Rate (lb/M) % Control Rate (lb/M) % Control
0 0 0 0
40 50 20 58
81 65 40 86
122 80 61 97
162 95 122 87
203 92 201 79Adapted from Christians, N.E. 1993. The use of corn gluten meal as a natural preemergent weed controlin turf. ITS No. 7. Intertec Publishing Corp., Overland Park, KS, p. 284-290.
Corn Gluten Meal for Weed Control
• High use rates (12-20 lb/M)– One to two applications annually
• Expensive: $25-$45 per application/M
• Pre-emergent only
• Overseeding limitations
• Fertility effect
Other Ways to Reduce Risk
• Use pesticides only when necessary– Integrated Pest Management
• Choose products with lower toxicities
• Follow ALL label instructions– Gloves, rates, disposal
• Remember…– Risk = Toxicity x Exposure!
Conclusion
• A little herbicide goes a long way if…
• Turf is properly managed!