Maximizing Preemergence Herbicide Performance in Tall Fescue Tim R. Murphy The University of Georgia

Tall Fescue/Southern Transition Zone Growth slows in high heat and humidity Susceptible to brown patch (only limited resistance in commercial varieties) Turf density decreases with resultant decrease in competitive ability Often reseeded annually or every other year

Differential large crabgrass control in tall fescue. Johnson, 1993

Preemergence herbicides are the foundation of annual grass control.

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

Preemergence Options for Tall Fescue

Annual Grass Control Ratings

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

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. Trifluralin is the most volatile, Surflan the least volatile. Losses from photodecomposition and volatilization

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

Maintain Healthy Turfgrass Manage the roots to have good shoots Soil testing is a must! Utilize cultural practices (fertility, irrigation, mowing height, etc.) to improve stress tolerance Keep mower blades sharp !

Brown Patch in Tall Fescue Rhizoctonia solani Favored by night temps. > 60 F. and > 10 hrs., foliar wetness for several days Cloudy weather, poor soil drainage, lack of air movement, late afternoon watering Severity increases with excessive N fertilization and on soils low in P and K

Smooth Crabgrass Control - Pendimethalin * * Rated 8/23/99

Smooth Crabgrass Control - Prodiamine Rated 8/23/99

Smooth Crabgrass Control - Oxadiazon Rated 8/23/99

Reseeding Restrictions

The majority of herbicides used for preemergence annual grass control are dinitroanilines and dithiopyr DNA’s Barricade Pendulum Surflan Balan Treflan Dimension Best used on established turf. Mitotic inhibitors. Relatively immobile in the soil Spring applications can thin fall-seeded fescue

Tolerance of Fall-Seeded Tall Fescue to Spring-Applied Preemergence Herbicides B. J. Johnson & T. R. Murphy The University of Georgia

Methods Seeded ‘Ky 31’ in mid-Sept., -Oct. and -Nov. Applied herbicides on Feb yr. study Recorded quality and density ratings following spring and early summer

Tolerance of Fall-Seeded Tall Fescue to Pre Herbicides

Results No herbicide reduced density of tall fescue seeded in mid-Sept. or mid-Oct. Pendimethalin, XL, Dimension, and Surflan reduced density 17 to 40% for fescue seeded in mid-Nov. in both yrs. In 1 of 2 yrs. Balan and Ronstar reduced density

Fall-Seeded Tall Fescue Related study showed that early-Nov. seeded tall fescue was tolerant to Feb. 1 + Apr. 1, Mar. 1 + May 1, or Apr. 1 + June 1 applications of Barricade at lbs. ai/acre –Prinster, SWSS Proc. 47:255.

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

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

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

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

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?

Timing Summer Annual Grass Control Late February to early March for crabgrass control Goosegrass two to four weeks later Early application (late January to early February) is OK due to slower herbicide decomposition during cool weather. (do only in well-established tall fescue)

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

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

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

Avoiding Phytotoxicity Read the label to make sure the herbicide is registered for use on the turf Apply the herbicide at the recommended rate and determine application intervals Test unfamiliar products and tank mixes on a small scale

Avoiding Phytotoxicity Keep sprayers calibrated and in good working order Agitate spray mixture Avoid application to stressed turfgrasses Keep accurate records of all applications