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

Presence of Weeds Usually Indicates Underlying Problem Turfgrasses adapted to the local environment resist weeds best

Good Turf Management Mowing Fertility Irrigation Turf species 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 Algae 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 Grassy Weed Control Difficult Annuals: crabgrass MSMA: retail Perennials: tall fescue, bentgrass, quackgrass, nimblewill Glyphosate (Roundup, Kleenup)

Creeping Bentgrass Poor quality seed Fine stolons easily ripped up 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 patch 1 ft stolons

Pre-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: pendimethalin dithiopyr (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 Broadleaf Herbicides 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 Herbicide Control Wild violet Formulations Esters volatile readily absorbed use during cool temps or hard-to-kill weeds Salts less volatile use during hot temps less smell

Weed 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! “Non-Toxic” Pesticides

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 LD50 CuSO4 Bordeaux Mixture Fungicide 11 Caffeine --- 192 2,4-D Various Herbicide 375-666 *Aspirin 1240 *Table salt 3320 Glyphosate Roundup 5800 3500 ppm = 10 oz ai/180 lb adult 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.

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 Fate Pesticide Applied Photodecomposition (Volatilize) (Drift) Runoff ? Plant Uptake & Degradation Thatch Adsorption Microbial decomposition Soil Chemistry Reactions 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 Adapted from Christians, N.E. 1993. The use of corn gluten meal as a natural preemergent weed control in 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!