Responding to Lawn Weed Management Questions

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

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

3. 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

4. Moss and Algae • Low light • Restricted air movement • Poor drainage • Often compounded by poor management

5. 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

6. Post-Emergent Grassy Weed Control • Difficult • Annuals: crabgrass • MSMA: status? Quinclorac-pros only • Perennials: tall fescue, bentgrass, quackgrass, nimblewill • Glyphosate (Roundup, Kleenup) • Sulfosulfuron is selective for TF, quackgrass-pros only

7. Why are Some Products Only Available to Professionals? • Special application equipment needed • Constant agitation required to keep water-insoluble products in suspension • New herbicides used at very low rates—homeowners lack precision measuring • Companies want to reduce issues resulting from misapplication • Money-EPA requires expensive data sets for each product’s use

8. Creeping Bentgrass & Rough Bluegrass • 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 • Mesotrione-pros only Bentgrass patch 1 ft stolons

9. 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 prodiamine dithiopyr (some post-emergent) siduron, mesotrione--OK for seeding

10. 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 Crabgrass and Quackgrass

11. 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 • Pros have newer products, low use rates, more environmentally friendly

12. 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

13. Weed and Feed Products • Herbicide impregnated on fertilizer prill • Post or pre-emergence • Post: Stick to leaves? • Pre: Timing?

14. “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!

15. 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!

16. Toxicity of Common Substances LD50 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.

17. 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.

18. Pesticide Fate Photodecomposition (Volatilize) Pesticide Applied (Drift) Runoff ? Plant Uptake & Degradation Thatch Adsorption Microbial decomposition Soil Chemistry Reactions and Decomposition Leaching?

19. Corn Gluten Meal • Accidental discovery • Research-based! • Activity • Herbicidal(?) • Fertility (10% N)

20. Corn Gluten Meal Application • 12-20 lb/M • Early spring • Late summer • Irrigate • Timing critical • Short-lived peptides

21. 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.

22. 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

23. 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!

24. Conclusion • A little herbicide goes a long way if… • Turf is properly managed!