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Oklahoma State University Stillwater, OK |
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Oklahoma Alfalfa |
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Oklahoma State University Stillwater, OK |
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Oklahoma Alfalfa |
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Webworms |
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Life Cycle and Damage. Webworms are larvae of small moths that complete several generations per year and often become quite abundant in alfalfa during summer months. When fully grown, these worms are about 3/4 inch in length, and have light green coloration with numerous black spots. As they develop, webworms spin silken webs over plant terminals, then feed on leaves, buds, and blossoms within the webs. Although extensive defoliation may not result from their feeding, webworms often consume fruiting structures and their webs interfere with pollination and seed set. Infestations by these worms can result in serious losses in seed production. Sampling and Control. As with other pests that have been discussed, it is important to assess population densities of webworms before alfalfa begins to bloom. Webworms can be counted in sweep samples taken for foliage-feeding caterpillars (20 sweeps in each of 5 areas/field). If the numbers of webworms exceed 3-5 /sweep (even in the absence of other foliage feeders) and silken webs cover 10 percent or more of the terminals, application of insecticide should be considered to prevent serious losses in seed production. It is important to use relatively high spray volumes (ground = 10 gal/acre; aerial = 2-4 gal/acre) to penetrate webs for effective control. Additional information on control of webworms can be found in OSU Extension Facts No. 7150.
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| Richard Berberet,
Alfalfa Entomologist Department of Entomology and Plant Pathology Oklahoma State University |
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