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Turfgrass Weed Management

Dr. Tim R. Murphy
Extension Weed Scientist
University of Georgia
Griffin, GA

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TABLE OF CONTENTS

Turfgrass Weed Management The Goal Turfgrass Weeds Develop A Plan Weed Management Strategy Identify the Weed Problem Weed Life Cycles Weeds can be a problem in all 12 months Integrated Weed Management Preventive Methods Cultural Methods Soil Fertility Effects on Weeds Weeds Favored in Compacted Soils Weeds Favored by High Soil Moisture Weeds Favored by Low Soil Moisture Maintain Healthy Turfgrass Preemergence herbicides are the foundation of annual grass control. 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. What is the best preemergence herbicide for turfgrasses?? It depends... Preemergence Herbicide Selection Preemergence Herbicide Selection Annual Grass Control Ratings Crabgrass spp. Crabgrass spp. Southern and Smooth Crabgrass Goosegrass Goosegrass Goosegrass and crowfootgrass Goosegrass Cultural Controls Core Aerification Ronstar (oxadiazon) Annual bluegrass Continuous annual bluegrass seed germination occurred from mid-Nov through early January Annual bluegrass control Preemergence Herbicides Preemergence Herbicides Irrigation Timing and Formulation Effect on Crabgrass Control with Pendimethalin Relative Volatility of Preemergence Herbicides Relative Solubility of Preemergence Herbicides Granular Formulations Fertilizer/Preemergence Products Fertilizer/Preemergence Products - Other Considerations Preemergence Herbicides - Formulation Effects Preemergence Herbicides - Formulation Effects Preemergence Herbicides - Formulation Effects Preemergence Herbicide Timing Suggested Application Dates Timing Summer Annual Grass Control Repeat Applications - Summer Guidelines - Preemergence Lack of Preemergence Herbicide Performance Post Summer Grass Control MSMA Use MSMA Alternatives MSMA Alternatives Post Goosegrass Control Poa Control with Kerb Annual Bluegrass Control Ryegrass Ryegrass Control Ryegrass Tall Fescue Dallisgrass Control Sandbur Bermuda Suppression in Zoysia Roundup Rate and Bermudagrass Control Bermuda Control with Roundup – 1 yr. Bahiagrass Avoiding Phytotoxicity Avoiding Phytotoxicity

SLIDE CONTENTS

Turfgrass Weed ManagementI. MethodsII. Grass Weed Control Tim R. Murphy Crop and Soil Sciences The University of Georgia The Goal Establish and maintain a high quality, nearly weed-free turfgrass. Turfgrass Weeds Reduce quality Reduce density Decrease aesthetic value or utility of the turfgrass. Develop A Plan Goals Economics Alternatives Benefits Weed Management Strategy Diagnose problem Evaluate control methods Select program Execute program Evaluate Identify the Weed Problem READ textbooks and periodicals Keep a diagnostic tool kit - hand lens, etc. Know the life cycle of the pest (What temp. does a specific weed seed germinate?) Is the weed the cause or effect of the problem? Confirm your diagnosis Weed Life Cycles Summer annuals - < 1 yr. Winter annuals - ə yr. Biennials - 2 yr. Perennials - > 2 yr. PPT Slide Weeds can be a problem in all 12 months. Integrated Weed Management Preventive Cultural Biological Mechanical Herbicides Preventive Methods State and federal laws Weed-free seed, plant material Topsoil (no nutsedge) Clean equipment Field borders Cultural Methods Adapted turfgrasses Fertility management Cultivation practices Irrigation Pest control Soil Fertility Effects on Weeds Low N - legumes, mosses High P - annual bluegrass High N - common chickweed Low soil pH - red sorrel, broomsedge Weeds Favored in Compacted Soils Annual bluegrass Goosegrass Prostrate knotweed Common lespedeza Path rush Weeds Favored by High Soil Moisture Sedges - purple nutsedge, green kyllinga Rushes Annual bluegrass Mosses Weeds Favored by Low Soil Moisture Prostrate spurge Poorjoe Common lespedeza Prostrate knotweed 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 ! Use the best species and cultivars for your location Preemergence herbicides are the foundation of annual grass control. PPT Slide 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. Relatively immobile in the soil PPT Slide What is the best preemergence herbicide for turfgrasses?? PPT Slide 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. - 53 to 58 F., 4 inch depth Light required PPT Slide Summer annual Crabgrass spp. PPT Slide 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 PPT Slide goosegrass crowfootgrass Goosegrass Cultural Controls Aerify to alleviate compaction Redirect traffic Control watering Encourage thick 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 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 Annual bluegrass Winter annual Germinates late summer-fall at soil temperatures around 70 F. Second germination flush in mid- to late-winter PPT Slide 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. Treflan (Team) 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 Relative Volatility of Preemergence Herbicides Relative Solubility of Preemergence Herbicides 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 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! Timing Summer Annual Grass Control Late February to early March for Georgia 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 Post Summer Grass Control MSMA is the most commonly used product in bermudagrass, tall fescue and zoysiagrass for crabgrass control Do not use MSMA on centipedegrass or St. Augustinegrass MSMA labeled for tall fescue but may cause severe injury during hot Georgia summers MSMA Use Most effective on seedling to 4 leaf crabgrass Apply when temperature is between 75 and 90°F. Repeat application(s) usually needed on well tillered crabgrass MSMA Alternatives Vantage (sethoxydim) is a grass specific herbicide Vantage may be used on centipedegrass Vantage is most effective on seedling to 4 leaf grasses Envoy (clethodim) may also be used, but only on centipedegrass sod farms MSMA Alternatives Acclaim Extra (fenoxaprop) and Fusilade II (fluazifop) are grass specific herbicides Acclaim Extra and Fusilade II may be used on zoysiagrass and tall fescue They are most effective on seedling grasses Post Goosegrass Control Illoxan (diclofop) will control goosegrass postemergence For use on bermudagrass golf courses only Close mowed (less than 1 inch) goosegrass is easier to control MSMA + Sencor will control goosegrass but causes more bermudagrass injury Poa Control with Kerb Excellent for annual bluegrass Will move with water and damage cool-season grasses Herbicide of choice for late spring Poa control after bermuda has greened up Kerb movement onto bentgrass Annual Bluegrass Control Bentgrass Greens One option is use of paclobutrazol (Trimmit) at 0.25 lb/ac in the fall followed by 2 to 3 applications in the spring. Pre’s tend to select for the perennial type Poa annua PPT Slide Roundup is the most effective Kerb will provide some help Illoxan will provide some control Reward and Finale ineffective Ryegrass Ryegrass Control PPT Slide Overseeding Clumpy ryegrass tall fescue cool-season perennial Roundup High rates of Kerb during winter months Corsair Dallisgrass Control Repeat applications of MSMA Usually 3 to 4 treatments required on a weekly schedule or spot spray with Roundup PPT Slide summer annual Sandbur spp. Bermuda Suppression in Zoysia Completely eradicate bermuda before planting zoysia and then buy clean zoysia Spot spray with Roundup Apply 3 to 4 applications of Acclaim Extra per year for 2 years Apply 2 applications of Fusilade II per year for 2 years Roundup Rate and Bermudagrass Control DAT = Days after Treatment Bermuda Control with Roundup – 1 yr. PPT Slide rhizome seedhead bahiagrass Repeat MSMA, or Manor Avoiding Phytotoxicity Read the label to make sure the herbicide is registered for use on the turf or plant Apply the herbicide at the recommended rate and determine application intervals Test unfamiliar products and tank mixes on a small scale Use separate sprayers for fungicides or clean thoroughly between applications Avoiding Phytotoxicity Keep sprayers calibrated and in good working order Agitate spray mixture Avoid application to stressed turfgrasses Keep accurate records of all applications