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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. Fall X 3,000,000 Plants 4,000,000 Tubers Acre Acre
Introduced weeds • Johnsongrass • Common lespedeza • Crabgrass • Broadleaf plantain • Water-hyacinth
Factors affecting seed germination • Oxygen • Light • Scarification • Temperature • Water
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
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
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.
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