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Basics of Turfgrass Weed Management

Tim R. Murphy
The University of Georgia
Crop and Soil Sciences

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TABLE OF CONTENTS

Basics of Turfgrass Weed Management What is a Weed? Is this plant a weed??? Human beings decide which plant is a Weed!!! Why are weeds an annual problem? Turf Weeds Weed seed survival insured by: Weeds are prolific seed producers Nutsedge Introduced weeds Factors affecting seed germination Why control weeds? Control vs. Eradication Weeds Why do we control weeds in turfgrasses? Turfgrass Weeds Annual Bluegrass (Poa annua) Develop A Plan The Goal Integrated Weed Management Preventive Methods Cultural Methods Southeast U. S. Turfgrasses Southeast U. S. Turfgrasses A Case Study - Oklahoma Herbicides - Turfgrass Species Soil Fertility Effects on Weeds Irrigation Weeds Favored by High Soil Moisture Weeds Favored by Low Soil Moisture Weeds Favored in Compacted Soils Weeds Weeds may indicate a nematode problem Mechanical Methods Mowing Weed Species Response to Mowing Why does mowing control tall-growing weeds? Why does mowing not control low-growing weeds? Kentucky Bluegrass Herbicides Herbicides Maintain Healthy Turfgrass Identify the Weed Problem Weed Thresholds - ?? Scouting Sites Scouting Sites Scouting Sites When to Scout? Developing a Weed Management Program

SLIDE CONTENTS

Basics of Turfgrass Weed Management Tim R. Murphy Crop and Soil Sciences The University of Georgia What is a Weed? A plant out of place A plant whose virtues have yet to be discovered A flower in disguise Is this plant a weed??? Common ragweed decreases crop yields, allergen Poison ivy skin rashes, fruit consumed by birds Tall fescue desirable turf and forage grass a weed in warm-season turfgrasses Human beings decide which plant is a WEED!!!! Why are weeds an annual problem? Seed and vegetative structure dormancy Prolific seed producers Spread of seed Weed seed survival insured by: Hard seed coat (testa) Deep burial After ripening mechanisms Germination inhibitors Weeds are prolific seed producers. Seed/Plant Broadleaf plantain 36,000 Lambsquarters >30,000 Crabgrass 53,000 Texas Panicum 23,000 Annual Bluegrass 2,000 Weeds - Nutsedge Spring 43,560 1 ft. Acre X 3,000,000 Plants 4,000,000 Tubers Fall Acre Introduced weeds Johnsongrass Common lespedeza Crabgrass Broadleaf plantain Water-hyacinth Factors affecting seed germination Oxygen Light Scarification Temperature Water Why control weeds? Control vs. Eradication Control -Process of limiting a weed infestation to a level that is economically or aesthetically beneficial. Eradication -Elimination of all plants and plant parts of weed species from an area. Weeds Compete with desirable plants for sunlight, moisture and nutrients May exert allelopathic effects Reduce yields or quality of harvested product Why do we control weeds in turfgrasses? Turfgrass Weeds Reduce quality - leaf width, shape, color differences Reduce density - outcompete turfgrasses, can lead to erosion Decrease aesthetic value or utility of the turfgrass. - difficult to mow, disrupt uniformity of playing surfaces, safety considerations, attract insects Develop A Plan Goals Methods Economics Alternatives Benefits The Goal Establish and maintain a high quality, nearly weed-free turfgrass. Integrated Weed Management Methods Preventive Cultural Biological – not available in turfgrasses Mechanical Herbicides Preventive Methods State and Federal laws Weed-free seed, sod, sprigs Weed-free topsoil, topdressing Clean equipment Field borders Cultural Methods Adapted turfgrasses Fertility Cultivation Water management Insect and disease control Southeast U. S. Turfgrasses Soil Fertility Effects on Weeds Low N - legumes, mosses, speedwell High P - annual bluegrass High N - common chickweed, ryegrass, annual bluegrass Low soil pH - red sorrel, broomsedge Weeds Favored by High Soil Moisture Sedges - purple nutsedge, green kyllinga Rushes Annual bluegrass Mosses, algae Alligatorweed Pennywort Weeds Favored by Low Soil Moisture Prostrate spurge Poorjoe Common lespedeza Prostrate knotweed Weeds Favored in Compacted Soils Annual bluegrass Goosegrass Prostrate knotweed Common lespedeza Path rush Weeds may indicate a nematode problem spurges Florida pusley prostrate knotweed Mechanical Methods Mowing Hand removal Why does mowing control tall-growing weeds? Reduces apical dominance of main stem Basal buds initiate growth Continued clipping depletes root carbohydrates Prevents weed seed formation Why does mowing not control low-growing weeds? Primary growing point is located beneath the mower blade. Kentucky Bluegrass Herbicides Herbicide – a chemical used to control, suppress or kill plants. Preemergence – applied before weed seeds germinate Postemergence – applied to emerged weeds Herbicides Turf species vary in tolerance Weed species vary in susceptibility Turfgrass species and weed identification is critical to herbicide selection!!!! 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 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 Thresholds - ?? Site - putting green, lawn, etc. People - expectations Weed - population dynamics Budget - dollars Scouting Sites Use zig-zag pattern Make random stops Scouting Sites Identify weeds and life cycle Record observations by area - ornamental beds - turfgrass areas * front lawn * back lawn Scouting Sites Record density by species Low - 1 to 10% Medium - 11 to 20% High - > 20% When to Scout? Mid-winter months - winter weeds Late-April to July - summer weeds Late summer - assess summer program Late spring - assess winter program Developing a Weed Management Program Prevent weed introduction Properly maintain turfgrasses Identify weeds and learn life cycle Initiate control practices Preventive Cultural Mechanical Herbicides