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

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

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.  Immobile in the soil

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

What is the best preemergence herbicide for turfgrasses??

It depends……….

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

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

Annual Grass Control Ratings

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

Southern crabgrass Smooth crabgrass

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

goosegrass  Summer annual  Prefers compacted areas that are overwatered

goosegrass crowfootgrass

Goosegrass Cultural Controls  Aerify to alleviate compaction  Redirect traffic  Control watering  Encourage dense turf

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

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

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

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

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.  Losses from photodecomposition and volatilization  Treflan (Team) is the most volatile, Barricade the least volatile.

Relative Solubility of Preemergence Herbicides

Preemergence Herbicide Volatility Herbicide Vapor Pressure (mm Hg) Relative Volatility Benefin1.0X Moderate Pendimethalin9.4 X Low Surflan2.5 X Very Low Barricade3.3 X Very Low Dimension4.0 X Low Kerb8.5 X Moderate Bensulide8.0 X Very Low Ronstar7.8 X Very Low Aatrex2.9 X Very Low

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

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 Herbicides - Formulation Effects Johnson and Murphy, 1991

Preemergence Herbicides- Formulation Effects Johnson and Murphy, 1991

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?

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

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.

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

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

Growth Regulator Herbicides

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.

Phenoxy + Dicamba Herbicides Herbicide2,4-DMCPPMCPA2,4-DPdicamba Weedar 64X MCPP-4X 2 Plus 2XX Four Power +XX Turf D + DPXX Trimec ClassicX (>)X (<)X Trimec SouthernX (<)X (>)X

Phenoxy + Dicamba Herbicides Herbicide2,4-DMCPPMCPA2,4-DPdicamba TriamineXXX Triamine IIX (>)X (<)X Tri-PowerX (<)X (>)X DissolveXXX TripletX (>)X (<)X (>) Triplet Sens.X (<)X (>)X (<)

Phenoxy, Dicamba, Picolinic Herbicides Herbicide2,4-DMCPAclopyralidtriclopyrdicamba LontrelX Turflon EsterX ConfrontXX Chaser (ester)XX Chaser II Am.XX Cool Power (ester) X (<) HorsePowerX (>)

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.

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

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

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

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.

Post Herbicide Use Guidelines  Repeat applications are most effective for tough perennials.  Apply during good growing conditions when adequate soil moisture is present.  Add a surfactant if called for on label.

Non-Target Plants  Check for restrictions on the use of herbicides around trees and shrubs.  Be very careful around vegetables and ornamentals with growth regulator herbicides.  Avoid applying dicamba and atrazine under shallow rooted ornamentals such as azalea and rhododendron.

Nonselective Broadleaf Control  Roundup Pro - slow acting (7-14 days) but provides the best control of perennials.  Reward - fastest burndown, poor perennial control, poor grass control.  Finale - Almost as fast as Reward, will leave a straight edge, very good on white clover and other legumes. Not good on perennials.

Lack of Post Herbicide Performance  Environmental stresses  Weed growth stage  Rain/irrigation wash-off  No adjuvant  Poor spray coverage

Lack of Post Herbicide Performance  Wrong rate  Wrong herbicide  No follow-up application  Mowing effects