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Purple nutsedge earns nod as 'world's worst' weedArkansas As fast as a speeding rhizome, more powerful than a gardener's patience and able to penetrate concrete and carpet in a concerted push--look, down in the lawn. They're flowers. They're grasses. They're the top 10 worst weeds in Arkansas, as nominated by Dr. John Boyd, weed scientist with the University of Arkansas Cooperative Extension Service. --No. 1. Purple Nutsedge--"Purple nutsedge is considered to be the world's worst weed," Boyd said. This plant can reproduce through seeds, rhizomes and tubers and is prolific. In a test plot of some 43,500 plants per acre, in one season, the purple nutsedge had increased to more than 3 million plants per acre with more than 4.4 million tubers per acre. "Purple nutsedge can grow through asphalt, plastic mulch, above-ground swimming pools and the floor of your house," Boyd says. Certainty provides suppression and is safe on all warm-season grasses. Sedgehammer provides some control when used on all lawn grasses. --No. 2. Annual Bluegrass--"Very adaptable winter annual found all round the state in about every location imaginable," he said. "Annual bluegrass is a prolific seed producer and capable of germinating 12 months per year, with most germination occurring from September to November." Bluegrass can be controlled by applying a pre-emergence herbicide such as prodamine or pendimethalin in late August. Roundup provides good control in completely dormant Bermudagrass. Revolver may be used for post-emergence control in Bermudagrass and zoysiagrass. --No. 3. Crabgrass--One crabgrass plant, left unchecked, can produce more than 50,000 seeds in one season," Boyd said. "Crabgrass matures rapidly going from seedling to flower in about 45 days during midsummer." The good news is crabgrass isn't difficult to control, but is ubiquitous. To control crabgrass, apply a pre-emergence herbicide in late February to early March. If the preemergence fails, one or two applications of MSMA at weekly intervals in bermudagrass and zoysiagrass only. --No. 4 Bermudagrass--Bermudagrass is the No. 1 lawn grass, but let it get into your garden and it's tough to remove. The grass is a perennial and spreads via stolons, rhizomes and seeds. Use sethoxydim, fluazifop or clethodim for control in landscape beds. Sethoxydim may be used in centipedegrass lawns. Fluazifop or fenoxaprop plus triclopyr ester can be used for control in tall fescue or zoysiagrass. --No 5. Yellow Nutsedge--This nutsedge is identifiable by the yellowish-brown seedhead and needle-like leaf tips. Very common north of I-40, this perennial weed spreads by tubers, rhizomes and seeds. While not as aggressive as its purple cousin, it is more cold-hardy. Certainty provides suppression and is safe on all warm-season grasses. SedgeHammer provides some control when used on all lawn grasses. --No. 6. Common Yellow Woodsorrel--The Woodsorrel uses a secret weapon that follows its innocent-looking yellow flowers. The okra-like fruit explode, ejecting seeds as far as 12 feet. Prevention and sanitation are the best methods of control. Don't let woodsorrel go to seed. Herbicides with 2,4-D plus dicamba and MCPP provide fair to good post-emergence control in tolerant turfgrasses. Products with metsulfuron and triclopyr tend to be more effective in tolerant turfgrasses. --No. 7. Prostrate Spurge--This summer annual is very drought tolerant. "It is that weed growing comfortably in the sidewalk crack when the temperature is 100 degrees Fahrenheit in the shade," Boyd said. There are plenty of control options for spurge. In tolerant turfgrasses, Metsulfuron is one of the best post-emergence treatments. Pendimethalin and prodiamine provide partial pre-emergence control and simazine and atrazine offer pre- and early post-emergence control. --No. 8. Mulberry Weed--This plant spreads by seed and is a prolific seed producer. "Seeds are mostly dropped near the mother plant, but some seeds are explosively dispersed--they can be thrown up to 4 feet," he said. "Plants can have two or more generations per season. Don't let this baby go to seed." This plant often rides in on nursery stock. Control should include exclusion, sanitation and herbicides such as Gallery and Barricade. --No. 9. Violets--Don't let the white or purple flowers fool you. Violets are "tough perennials that tolerate most broadleaf herbicides used in lawns," Boyd said. "They spread rapidly, especially in shady areas with thin turfgrass and reproduce from seeds and rhizomes." Control is very difficult. Metsulfuron is the best option in tolerant turfgrasses. "The best course may be to adopt it as a groundcover." --No. 10. Wild Garlic--Wild garlic plants add pungency to the weekly lawn mowing. This perennial can be identified by their slender, hollow cylindrical stems, as opposed to wild onion, which has solid stems. To control, dig up the plants, if there are only a few. Metsulfuron is the best option in tolerant turfgrasses. Otherwise, herbicides with 2,4-D provide partial control. For more information on weed control, visit www.uaex.edu or www.arhomeandgarden.org. The Cooperative Extension Service is part of the Division of Agriculture. Date: 6/4/07
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