Responding to Lawn Weed Management Questions Dr. John Stier University of Wisconsin-Madison Environmental Turfgrass Extension Specialist.

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!