Responding to Lawn Weed Management Questions

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Responding to Lawn Weed Management Questions

• Dr. John Stier
• University of Wisconsin-Madison
• Environmental Turfgrass Extension Specialist

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Presence of Weeds Usually Indicates Underlying
Problem

• Turfgrasses adapted to the local environment
  resist weeds best

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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

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Moss and Algae

• Low light
• Restricted air movement
• Poor drainage
• Often compounded by poor management

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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

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Post-Emergent Grassy Weed Control

• Difficult
• Annuals crabgrass
• MSMA retail
• Perennials tall fescue, bentgrass, quackgrass,
  nimblewill
• Glyphosate (Roundup, Kleenup)

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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 patch
1 ft
stolons
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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

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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
• Cant pull plant
• Rhizomes

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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

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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

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Weed and Feed Products

• Herbicide impregnated on fertilizer prill
• Post or pre-emergence
• Post Stick to leaves?
• Pre Timing?

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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!

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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!

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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.
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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.

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Pesticide Fate
Photodecomposition
(Volatilize)
Pesticide Applied
(Drift)
Runoff ?
Plant Uptake Degradation
Thatch Adsorption
Microbial decomposition
Soil Chemistry Reactions and Decomposition
Leaching?
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Corn Gluten Meal

• Accidental discovery
• Research-based!
• Activity
• Herbicidal(?)
• Fertility (10 N)

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Corn Gluten Meal Application

• 12-20 lb/M
• Early spring
• Late summer
• Irrigate
• Timing critical
• Short-lived peptides

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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.
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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

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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!

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Conclusion

• A little herbicide goes a long way if
• Turf is properly managed!