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Turfgrass Weed Biology and Identification

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

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TABLE OF CONTENTS

Turfgrass Weed Biology and Identification Why do we control weeds in turfgrasses? Weeds Turfgrass Weeds Control vs. Eradication Developing a Weed Management Program Why are weeds an annual problem? Characteristics of Most Weeds Characteristics of Most Weeds Characteristics of Most Weeds Characteristics of Most Weeds Weed Competition Weed Competition Weed Identification is a Key Step in Control Traditional Plant Identification is Based on Recognizing Floral and/or Reproductive Features Mowing Removes Identification Characteristics of Many Turf Weeds Identifying Turf Weeds Depends on Primary Vegetative Structures Leaf Leaf Arrangement Shape of cotyledons or true leaves Leaf margin Major vegetative parts of grasses used in identification Stolons and Rhizomes Tubers and Rhizomes Tubers and Rhizomes Bulbs Weed Life Cycles Summer Annuals Summer Annuals Crabgrass Goosegrass Common lespedeza; Prostrate knotweed Prostrate spurge Chamberbitter, cannonball weed, gripeweed Winter Annuals Winter Annuals Annual bluegrass Poa annua L. Common chickweed Lawn burweed (spurweed) Henbit Hairy bittercress Biennials Shiny cudweed; Purple cudweed Warm-Season Perennials Warm-Season Perennials Dallisgrass Kyllinga; Sedge Virginia Buttonweed Purple Nutsedge - Cyperus rotundus Yellow Nutsedge - Cyperus esculentus Nutsedge: purple vs yellow Cool-Season Perennials Cool-Season Perennials Perennial ryegrass; Wild garlic Wild garlic Dandelion Wild violet; Ground ivy Identify the Weed Problem "Weeds of Southern Turfgrasses" "Color Atlas of Turfgrass Weeds" Turfgrass Web Pages UGA

SLIDE CONTENTS

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 Grass Broadleaf Crabgrass species Spotted spurge Foxtail species Common lespedeza Goosegrass Prostrate knotweed Sandbur Sedges: annual sedge Southern crabgrass Smooth crabgrass Goosegrass Common lespedeza Prostrate knotweed 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 Grass Broadleaf Annual bluegrass Chickweed species Henbit Lawn burweed Speedwell species Knawel Hop clover Annual bluegrass Poa annua L. Boat shaped leaf tip Common chickweed Lawn burweed (spurweed) henbit Henbit Hairy bittercress 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 Grass Broadleaf Dallisgrass Virginia buttonweed Bahiagrass Smutgrass Sedge / kyllinga species: green and false-green kyllinga, purple and yellow nutsedge Dallisgrass Kyllinga Sedge spp. Virginia buttonweed 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 Cool-Season Perennials Germinate in fall or winter Can produce seed in the first spring 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) Cool-Season Perennials Grass Broadleaf Perennial ryegrass Ground ivy Tall fescue In. mock strawberry Dandelion Wild violet Yellow woodsorrel White clover Grass-Like: Wild garlic Perennial ryegrass clumps Wild garlic Wild garlic bulbs and bulblets Dandelion Dandelion Wild violet Ground ivy 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 ACES - ANR-616 UGA-CES $14.00 www.amazon.com * 214 weed species *575 color photos *Control info for each weed $88.00 Turfgrass Web Pages www.georgiaturf.com or .org 437 photographs of 193 weeds Control recommendations Popular articles Links to turfgrass organizations, GA automated weather network