Weed Control in Turfgrass Systems

1. Weed Control in Turfgrass Systems Turfgrass IPM Workshop November 11, 2011 Sarah J. Wilhelm Colorado State University Fort Collins CO

2. Causes of Turf Weed Problems • Planting poor quality seed or sod • Weak, non-competitive turf • Improper species or cultivar selection • Poor management practices • Damaged by traffic, stress, pests

3. Use Weed-Free Seed!

4. Poa trivialis Roughstalk bluegrass Creeping bentgrass

5. Adequately fertilized turf Underfertilized turf

7. Mowing Height Affects Weed Seed Germination and Weed Vigor

8. Necrotic Ring Spot and Weeds

9. Integrated Weed Management Program for Turf • Prevent weed introduction • Properly maintain turfgrasses • Identify weeds and learn life cycles • Utilize and evaluate control practices • Cultural • Mechanical • Biological • Herbicide Use

10. Good Cultural Practices

11. Weeds Associated With Compacted Soils • Annual bluegrass • Goosegrass • Knotweed • Prostrate Spurge

12. Weeds Associated With Moist or Poorly Drained Soils • Annual bluegrass • Roughstalk bluegrass • Barnyardgrass • Bentgrasses

13. Weeds Associated With Infertile (Low Nitrogen) Soils • Black medic • Plantain • White Clover

15. Importance of Weed ID • Learn life cycle and growth preferences • Best ways to manage with cultural practices • Effective and LEGAL herbicide use

16. Warm-Season (C4) Species • Most are annuals • Crabgrass, foxtails, goosegrass, sandbur, barnyardgrass • Purslane, spurge, knotweed, puncturevine • Aggressive competitors with cool-season (C-3) grasses during the summer months

17. Cool-Season (C3) Species • Bluegrasses, ryegrass, fescues, bentgrasses are cool-season turf species • Dandelion, thistle, bindweed are cool-season broadleaf weeds • Quackgrass, bromegrass, annual bluegrass are perennial weedy grasses • Grow best (and are easiest to control) during spring and fall

18. Weed ID Web Sites North Carolina State University http://www.turffiles.ncsu.edu/turfid/ Michigan State University http://www.msuturfweeds.net/

19. Weed ID and Management Books • Color Atlas of Turf Weeds. 2008. John Wiley and sons. • Weeds of the West. 1991. The University of Wyoming. • Identifying Turf and Weedy Grasses of the Northern United States. http://pubsplus.uiuc.edu/C1393.html

20. Classes of Turf Weed Problems • Annual grassy weeds • Perennial grassy weeds • Sedges • Broadleaf (dicot) weeds

21. Grassy Weed Control is Difficult • Infestation often goes unnoticed until it has become a major problem • Selective control can be difficult • Species often related – sometimes same genus • Limited chemistry/number of herbicides

22. Annual Grassy Weeds Summer Annuals • crabgrass • goosegrass • foxtails • barnyardgrass • annual (?) bluegrass • winter annual bromes

23. Preemergence Herbicides • benefin (Balan) • benefin + trifluralin (Team) • bensulide (Betasan) • corn gluten meal (Amaizing Lawn, WOW, many others) • dithiopyr (Dimension) • isoxaben (Gallery) – broadleaf weeds only • oxadiazon (Ronstar) • pendimethalin (Pre-M, Pendulum, Scotts home products) • prodiamine (Barricade) • siduron (Tupersan) – for use at time of seeding • mesotrione (Tenacity) – both pre- and postemergence for annual grasses

25. Pre-emergence Herbicides… DON’Tkill weeds seeds DON’T sterilize the soil DON’Tcontrol weeds you can already see (except for dithiopyr/Dimension) DON’Tharm trees and other landscape plants whose roots are growing in the lawn CAN harm the roots of desirable turf

26. Annual Grass Control Ratings

27. Corn Gluten Meal for Natural/Organic Weed Control • Preemergence herbicide activity ONLY • Excellent N source (10% N) • Cost is about $1.00/pound • Use rate of 20 pounds/1000 sq. ft. provides 2 lbs. N/1000 • Processed CGM provides moderate control of crabgrass and other annual weeds • Will not provide long-term control of perennial weeds • Raw corn meal is NOT effective • Must use licensed sources of GGM to apply legally!

28. Causes of Unsatisfactory Preemergence Herbicide Performance • Applied after weed emergence • Rate applied was too low • Non-uniform application • Insufficient (at application) rainfall or irrigation • Excessive rain immediately after application • High rainfall year • Poor site drainage • Drought • Excessive/prolonged summer heat • Clippings collected before preemergent incorporated

29. Preemergent herbicide skip

30. Preemergence Herbicide Efficacy • Loss of activity may occur if not watered in within 7 to 10 days. • Losses from photodecomposition and volatilization can be important, especially with sprayable formulations • Avoid clipping collection

31. Single application at higher rate 1st Application 2nd Application Split Preemergent Herbicide Applications Phytotoxicity level Effective control level Herbicide Concentration Time

32. Perennial Weedy Grass Species • Tall fescue • Quackgrass • Bromegrass • Bentgrass • Zoysiagrass • Bermudagrass • Poa annua • Poa trivialis

33. Sources of Perennial Grassy Weeds • Contaminated seed or sod • Propagules present in soil at establishment • Introduced in topsoil, organics, topdressing, nursery materials (tree balls) • Encroachment from adjacent landscape (neighbor lawns, golf courses, farmland, rangeland) • Tracking by equipment, people, animals • Intentionally planted

35. Zoysiagrass patches in Kentucky bluegrass lawn

36. Managing Perennial Grassy Weeds • Glyphosate (Roundup), followed by reseeding or sodding • Learn to tolerate the different grass species There are new herbicides available for application by lawn care professionals that can be used to SELECTIVELY remove tall fescue, creeping bentgrass, rough bluegrass, quackgrass, windmillgrass, nimblewill and bermudagrass from Kentucky bluegrass lawns. PROPER IDENTIFICATION IS ESSENTIAL!!!

37. Rough bluegrass (Poa trivialis)

39. Quackgrass (Elytrigiarepens) • Coarse, blue-green leaves • Aggressive rhizome former • Rolled vernation • Early spring green-up • Common ag and ditchbank weed • Can be selectively controlled in bluegrass turf with Certainty herbicide (sulfosulfuron)

40. Tenacity (mesotrione) • Has a novel mode of action based on a naturally produced compound from the bottlebrush plant (Callistemon citrinis) • Absorbed by leaves, shoots, and roots and rapidly translocated in the xylem and phloem of susceptible plants • Prevents carotenoid production in leaves, leading to destruction of chlorophyll and cell membranes • Highly active at low use rates as a pre- and post-emergence herbicide • Provides selective broad-spectrum dicot and monocot weed control in a number of turf species • Can use at or prior to seeding of proposed labeled turfgrass species • Low toxicity to wildlife and aquatic organisms and short persistence in the environment

41. Mesotrione (Tenacity) for Bentgrass Control in Ryegrass and Kentucky BluegrassSyngenta Company • 2 applications 0.25 lb ai/A, at 10-14 interval • 3 applications 0.17 lb ai/A, at 10-14 day interval • 80-90% control at 15 weeks after treatment • Preemergent and postemergent activity on crabgrass, some broadleaf weeds

42. Grasses and Sedges Controlled by Tenacity Barnyardgrass (pre and post) Creeping bentgrass (post) Crabgrass species (pre and post) Foxtail, Yellow (pre and post) Goosegrass (pre and post) Nimblewill (post) Yellow nutsedge (post) Windmillgrass (post)

43. Turf Species Labeled for Tenacity • Kentucky bluegrass (including Texas x KBG hybrids) 0.16-0.25 lb. ai/a • Perennial ryegrass – 0.16 lb. ai/a • Tall fescue 0.16-0.25 lb. ai/a • Fine fescues (red, Chewings, hard) 0.16 lb. ai/a

46. Dicot Weed Control Perennials • Dandelion, clover, bindweed, thistle, plantain, violet Annuals • Spurge, puncturevine, oxalis, purslane Prevention • Proper establishment • Ongoing maintenance Herbicides • Gallery (good), grass preemergents (fair) • Many postemergent options

47. Dicot Weeds Can Be Difficult to Control • Control is contingent upon herbicide uptake and translocation • Death of the weed may be slow • Mature weeds may not be controlled completely

48. Postemergent Herbicide “Failure” • Weeds curl and discolor, but don’t die • Weeds appear to have died, but come back • Reasons... • Weed species • Weed age • Weed health/vigor

49. Seedlings are easier to control than are mature weeds

50. Drought-stressed weeds • poor herbicide uptake • poor translocation • difficult to kill • Actively growing weeds • good herbicide uptake • rapid translocation • more easily killed