Turfgrass Herbicide Use Characteristics

1. Turfgrass Herbicide Use Characteristics Tim R. Murphy The University of Georgia

2. Preemergence herbicides are the foundation of annual grass control.

3. Weed seeds germinate and are controlled as they come in contact with the herbicide. Herbicide layer Turfgrass roots below the herbicide layer Preemergence herbicides do not prevent weed seeds from germinating.

4. Preemergence Options

5. DNA’s Barricade Pendulum Surflan Balan Treflan Dimension Best used on established turf. Mitotic inhibitors. Immobile in the soil The majority of herbicides used for preemergence annual grass control are dinitroanilines and dithiopyr

6. Ronstar (oxadiazon) • Not a mitotic inhibitor • Preferred herbicide for sprigging or high traffic areas (athletic fields, tees, etc.) • Preferred herbicide for preemergence goosegrass control • Will control crabgrass but is more effective on goosegrass

7. What is the best preemergence herbicide for turfgrasses??

8. It depends……….

9. Preemergence Herbicide Selection • Turfgrass species • Weed species • Immature vs. established • Time of year • Irrigation capabilities • Renovation plans

10. Preemergence Herbicide Selection • Granular or spray equipment • Desired control level • Application frequency • Ornamental tolerance • Cost??

11. Annual Grass Control Ratings

12. Crabgrass spp. • Summer annual • At least 5 species in GA (tropical, smooth, large, southern, blanket) • Germinates at soil temps. - 53 to 58 F., 4 inch depth • Light required

13. Southern crabgrass Smooth crabgrass

14. Goosegrass • Summer annual • Germinates - soil temp. 4 inch depth averages 60 to 65 F. • Usually germinates 2 to 6 weeks later than crabgrass • Light required

15. goosegrass • Summer annual • Prefers compacted areas that are overwatered

16. crowfootgrass goosegrass

17. Goosegrass Cultural Controls • Aerify to alleviate compaction • Redirect traffic • Control watering • Encourage dense turf

19. Core Aerification • Previously thought to break up herbicide layer and reduce weed control • Research shows little increased crabgrass or goosegrass due to core aerification

20. Annual bluegrass • Winter annual • Germinates late summer-fall at soil temperatures around 70 F. • Second germination flush in mid- to late-winter

21. Continuous annual bluegrass seed germination occurred from mid-Nov. through early January in Knoxville, TN. Callahan and McDonald, 1992

22. Annual bluegrass control Preemergence Control • Barricade, Pendulum • Surflan, Dimension • Balan, Ronstar • Kerb • Atrazine, Simazine Boat shaped leaf tip annual bluegrass

23. Preemergence Herbicides • Need rainfall or irrigation (1/2 inch) • Do not control emerged weeds

24. Preemergence Herbicides • If irrigation is not available, apply well in advance of expected weed germination to allow for an activating rainfall. • Loss of activity may occur if they are not watered in within 7 to 10 days. • Losses from photodecomposition and volatilization • Treflan (Team) is the most volatile, Barricade the least volatile.

25. Relative Solubility of Preemergence Herbicides

26. Preemergence Herbicide Volatility

27. Irrigation Timing and Formulation Effect on Crabgrass Control with Pendimethalin 0 = watered in immediately 7 = watered in 7 days after application GR = granular, WP = Sprayable

28. Granular Formulations • Poor Distribution of Active Ingredients: • Spreader not calibrated, changes with age • Bag settings are only guidelines • Spreader and/or product cause a skewing of product distribution over the turf • Particle size too large for uniform coverage • Lower application rates reduce uniform coverage

29. Fertilizer/Preemergence Products • Correct fertilizer analysis?? • Time of year?? • N-release characteristics?? • Supplemental fertilizer applications?? • Supplemental herbicide applications??

30. Fertilizer/Preemergence Products - Other Considerations • Uniform coverage required • Uniform particle size is important • Release characteristics of fertilizer product • Control equivalent to sprayable and granular products

31. Preemergence Herbicides - Formulation Effects Yelverton, et al., 1996

32. Preemergence Herbicides- Formulation Effects Johnson and Murphy, 1991

33. Preemergence Herbicides- Formulation Effects Johnson and Murphy, 1991

34. Preemergence Herbicide Timing • Soil temperatures can vary in a neighborhood - south facing slopes warm earlier in the Spring • Coarse textured soils warm more quickly than fine-textured soils • Most preemergence herbicides are degraded by soil microorganisms - activity is less at 45 degree vs. 70 degree soil temp. Most warm-season grassy weeds germinate at 55 to 65 F. APPLY EARLY • Can the site be irrigated for activation?

35. Suggested Application Dates • North Georgia • Spring, March 1 - 20 • Fall, August 20 - Sept. 15 • South Georgia • Spring, Feb. 10 - March 1 • Fall, Sept. 20 - Oct. 15 • Early is always better than late!

36. Timing Summer Annual Grass Control • Late February to early March for crabgrass control • Goosegrass two to four weeks later • Early application (late January, February) is OK due to slower herbicide decomposition during cool weather.

37. Repeat Applications - Summer • Space 8 to 10 wks apart • Apply 1/2 X fb 1/2X • May improve control of crabgrass and goosegrass

38. Guidelines - Preemergence • Labeled products only • Established turfgrass • Apply before weed emergence • Need rainfall or irrigation within 5 days • Consider split applications • Delay mowing until after incorporation • Know future plans

39. Lack of Preemergence Herbicide Performance • Applied after weed emergence • No rainfall or irrigation • Excessive rain after application, high rainfall year • High rainfall year • Poor site drainage • Drought • Rate too low • Mow/Bag before incorporation

40. Broadleaf Control • Most broadleaf control is done with postemergence herbicides. • The essential broadleaf herbicides are: • Postemergence - growth regulators and sulfonylureas • Pre and post – atrazine, simazine, metribuzin. • Pre only - Gallery

41. Growth Regulator Herbicides

42. Broadleaf Herbicides • There are many growth regulator combinations on the market. • Mixtures of broadleaf-active herbicides tend to control more weed species than each individual component herbicide.

43. Phenoxy + Dicamba Herbicides

44. Phenoxy + Dicamba Herbicides

45. Phenoxy, Dicamba, Picolinic Herbicides

46. Post Herbicide Use Guidelines • Try to avoid spraying warm-season grasses during transition. • Shade grasses are less herbicide tolerant than grasses growing in full sun. • Spray when wind speeds are less than 5 mph.

47. Post Herbicide Use Guidelines • Avoid stress conditions (> 90 F.) • Avoid spring transition on warm-seasons • Repeat applications • Do not mow 24 to 48 hours before or after application • Rainfall and irrigation effects

48. Post Herbicide Use Guidelines • Do not water for 12-24 hours. • Need a rain free period of at least 6 hours. • Avoid extreme temperatures. Apply when temperatures are between 40 and 80°F.

49. Examples of Rain-Free Periods • MSMA - 24 hours • Trimec Classic - 24 hours • Basagran T/O - 8 hours • Finale - 4 hours • Vantage - 1 hour

50. Post Herbicide Use Guidelines • Annual weed control is excellent in the seedling stage and poor as the weed matures • Perennial weeds are more susceptible in the Spring or Fall because root reserves are usually depleted and the weed has less recovery potential • Apply to actively growing weeds - the cuticle is more easily penetrated • Sprays give better control than granules.