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 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

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: retail
Perennials: tall fescue, bentgrass, quackgrass, nimblewill
Glyphosate (Roundup, Kleenup)

7. 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

8. 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

9. 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

10. 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

11. 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

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

13. “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

14. 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!

15. Toxicity of Common Substances
LD50
CuSO4
Bordeaux Mixture
Fungicide 11
Caffeine
---
192
2,4-D
Various
Herbicide
*Aspirin
1240
*Table salt
3320
Glyphosate
Roundup
5800
3500 ppm = 10 oz ai/180 lb adult
Source: Pesticide profiles: Toxicity, environmental impact, & fate M.A. Karmin (ed). Lewis Publishers
*Source: Applied weed science M.A. Ross & C.A. Lembi. Prentice-Hall.

16. 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.

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

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

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

20. Crabgrass Reduction in Field Trials of Corn Gluten Meal on Kentucky Bluegrass
Adapted from Christians, N.E The use of corn gluten meal as a natural preemergent weed control
in turf. ITS No. 7. Intertec Publishing Corp., Overland Park, KS, p

21. 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

22. 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!

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