Callaway County
Callaway County
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Jarman's Weekly Agronomy News August 23, 2000 |
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Army Worms in Lawns |
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During the past three weeks there have been reports of severe armyworm infestations in lawns throughout the state beginning in the south and moving north. Calls have come from the northwest, west, southwest, and central regions concerning "lots of worms in my lawn!" Most of these infestations appear to be armyworms, most likely the fall armyworm. The identification of worms attacking local lawns can be confirmed at the Callaway County Extension Center. Some species of armyworms and cutworms can cause serious damage to all types of lawns. The adult moths have forewings with a rather common background color of dull brown, gray, and black, with no outstanding prominent identifying marks. They fall into a rather large group commonly known as "LBMs" or little brown moths. The larvae (caterpillars) have background colors of essentially dull gray or brown to nearly black, but interspersed with minor amounts of brighter colors, mainly in the stripes. Black cutworms feed at the base of the lawn plants. Leaves and stems are cut off but may not be eaten. This feeding forms brown spots, 1-2 inches in diameter. Birds feeding extensively in a grassy area may indicate the cutworm's presence. Cutworms excavate a hole into the ground to hide during the day. During the night they leave the holes to feed on plant material. The fall armyworm feeds on grass leaf blades and, when numerous, can eat grass down to the ground, causing bare areas. Armyworms may hide during the day in the thatch, but older larvae do not hide during the day but feed continuously. Fall armyworm feeding damage is similar in appearance to that caused by excessive fertilization or herbicide injury. The presence of armyworms can be verified by parting the grass stems to the ground and looking for the presence of worms, chewed leaves, or piles of small, greenish to brown colored pellets (manure). These waste piles will be very noticeable in heavily infested areas. The black cutworm and fall armyworms migrate north each year from the southernmost regions of North America. Black-light trap catches determine the annual appearance of the moths in the Midwest. Black cutworm arrival in Callaway County is determined from pheromone trap catches. In mid-Missouri, black cutworm moths usually begin arriving in April and May, and fall armyworm moths arrive in July. Callaway County's first black cutworms were caught on March 22 this spring. There are at least 2 generations each season before the moths migrate south in the fall. For serious worm infestations chemical controls may be required. Liquid insecticide applications work best because they leave a residue on the foliage. So, no watering or mowing should be done for 24 hours after application. Granular insecticide formulations generally are less effective because they sift into the thatch on the ground and require water to be activated. Insecticides labeled for cutworms and armyworms and available for homeowner application include acephate (e.g. Orthene), carbaryl (e.g. Sevin), chlorpyrifos (e.g. Dursban), cyfluthrin (e.g. Advanced Garden Spray), and diazinon. There are other insecticides available for cutworm and armyworm control but they are restricted-use chemicals and must be applied by commercial applicators only. Although the fall armyworm and black cutworm are primarily leaf feeders, they can defoliate large numbers of plants to such an extent that, when coupled with summer heat stress, may cause major thinning of the lawn. Renovation and reseeding of the thinned areas may be required in mid-September. Refer to the University of Missouri Guide Sheet 6700: Lawn Establishment and Renovation for step by step instructions. Information for this article is from Drs. Bruce Barrett and Erik Ervin, located in the Departments of Entomology and Horticulture at the University of Missouri - Columbia, 573-882-3446 and 573-884-2266.
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