Turfgrass Weed Biology and Identification Tim R. Murphy The University of Georgia
Why do we control weeds in turfgrasses?
Weeds • Compete with desirable plants for sunlight, moisture and nutrients • Reduce yields or quality of harvested product
Turfgrass Weeds • Reduce quality - leaf width, shape, color differences • Reduce density - out-compete 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
Control vs.Eradication Control Process of limiting a weed infestation to a level that is beneficial (economics, aesthetics, safety, etc.). Eradication Elimination of all plants and plant parts of weed species from an area.
Developing a Weed Management Program • Prevent weed introduction • Properly maintain turfgrasses • Identify weeds and learn life cycle • Initiate control practices • Preventive • Cultural • Mechanical • Herbicides
Why are weeds an annual problem? • Seed and vegetative structure dormancy • Prolific seed producers • Spread of seed (wind, birds, humans, etc.) • Turfgrass culture selects tolerant species • Monoculture • Mowing
Characteristics of Most Weeds • High reproductive output Some weeds produce 1000’s of seeds per plant • Bimodal reproduction (more than one way to reproduce) Dandelion – seeds and taproot fragments Virginia buttonweed – seeds, stem fragments, roots
Characteristics of Most Weeds • Discontinuous germination or sprouting Weed seeds can remain dormant in the soil for many years and germinate sporadically. Crop and turf species are bred to NOT have dormancy – hence all seeds germinate at the same time.
Characteristics of Most Weeds • Highly dispersible Weeds must be able to colonize and invade. • Ability to Withstand Environmental Extremes Ability to survive unexpected events. Annual bluegrass and smooth crabgrass are found throughout the entire United States. (tremendous genetic diversity)
Characteristics of Most Weeds • Earliness Many weeds germinate early and grow faster and taller than desired turf. Thus they are capturing resources (light, moisture, nutrients) also needed by the turf. Various weed species found at any time of the year.
Weed Competition Competition will occur if there is one limiting resource needed by two or more plants. Weeds compete for the following resources. Light Water Nutrients Space
Weed Competition Weeds efficiently compete because of: Early germination Rapid seedling growth Large leaf area Extensive root systems
Tubers Thickened portions of rhizomes or roots, serving for food storage and also for propagation (yellow nutsedge example) Rhizomes Underground stems that can emit roots from the lower side and leafy stems from the upper side (green kyllinga ex.)
Tubers and Rhizomes Weeds that produce tubers include purple nutsedge, yellow nutsedge and Florida betony. Rhizomatous turfgrasses include bahiagrass, bermudagrass, Kentucky bluegrass, tall fescue and zoysiagrass. Rhizomatous weeds include dallisgrass, nimblewill and kyllinga species.
Bulbs Short, vertical, underground organs for food storage or reproduction on which specialized leaves prominently develop (wild garlic)
Weed Life Cycles Weeds are classified as… • Annuals (summer and winter) • Biennials • Perennials (warm-season and cool- season)
Summer Annuals • Germinate in spring or early summer • Produce seed in the summer • Die with cold weather or frost • Live for only ONE growing season!
Summer Annuals GrassBroadleaf Crabgrass species Spotted spurge Foxtail species Common lespedeza Goosegrass Prostrate knotweed Sandbur Sedges: annual sedge
Southern crabgrass Smooth crabgrass
Prostrate knotweed Common lespedeza
Prostrate spurge Milky sap
Chamberbitter, cannonball weed, gripeweed
Winter Annuals • Germinate in fall or early winter • Over-winter (very slow growth) during coldest months • Actively grow and produce seed in the spring • Die in summer as temperatures rise • Live for only ONE growing season!
Winter Annuals GrassBroadleaf Annual bluegrass Chickweed species Henbit Lawn burweed Speedwell species Knawel Hop clover
Annual bluegrass Poa annua L. Boat shaped leaf tip
Biennials • Germinate in fall or spring when conditions are favorable • Usually found in rosette stage in 1st Yr • Produce seed and die in the 2nd growing season
Shiny cudweed Purple cudweed
Warm-Season Perennials • Germinate in spring or summer • Can produce seed in the first summer • Can produce seed or reproduce by vegetative means indefinitely (survive for many years due to underground structures such as taproots, rhizomes, tubers, bulbs and aboveground structures such as stolons)
Warm-Season Perennials GrassBroadleaf Dallisgrass Virginia buttonweed Bahiagrass Smutgrass Sedge / kyllinga species:green and false-green kyllinga, purple and yellow nutsedge
Sedge spp. Kyllinga
Purple Nutsedge – Cyperus rotundus • Introduced, native to Eurasia • S. East U.S., CA and AZ • Ranked world’s worst weed • Forms chains of interconnected tubers • Prefers medium to fine-textured soils • Highly adapted to compacted soils
Yellow Nutsedge – Cyperus esculentus • Native to North America • Found in all of U.S. • Ranked 16th worst weed in world • Forms tubers • Commonly found in sandy soils • Thrives in non-compacted soils