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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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Lygus Bugs |
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Life Cycle and Damage. Although there are numerous species of plant bugs found in alfalfa, those that pose the greatest threat to seed production such as the tarnished plant bug are classified in the genus Lygus and are usually referred to as Lygus bugs. Nymphs of the Lygus bugs are light green in color and often mistakenly identified as aphids. However, they are much more active than aphids, often crawling rapidly over the plant foliage. Adults are yellow to brown in color and typically about 1/4 inch long. These insects overwinter as adults in alfalfa fields or adjacent areas with abundant grasses/weeds that provide a protective habitat. Lygus bugs complete several generations per year and may be present in large numbers in summer months. Nymphs and adult Lygus bugs feed with piercing-sucking mouthparts to remove plant fluids from buds, blossoms, and green seed pods, causing these structures to die and drop from plants. In the presence of high population densities of Lygus bugs, seed set and maturation may be reduced by nearly 100%. Much of the flower drop that occurs in alfalfa seed fields that is often attributed to dry weather may in fact be due to feeding by Lygus bugs. Sampling and Control. Fields in which seed production is planned should be sampled by sweeping before bloom so that, if necessary, controls may be applied before pollinators are present. As Lygus bugs are flying insects and may migrate into fields in large numbers within short time spans, it is important that sampling be conducted as alfalfa enters the bud stage. At least five samples of 5 sweeps each should be taken in each 30-acre area of alfalfa. Spraying is recommended when there are an average of 2 Lygus bugs/sweep. Spraying after the onset of blooming is not recommended as it may result in mortality of pollinators. However, if large numbers of these insects have migrated into seed production fields after bloom has begun, it may be necessary to apply insecticide. If bee colonies have been placed in the field for pollination, they must be removed before spraying. Spraying should be done in late evening or early morning when pollinators are not active. Additional information on control of Lygus bugs can be found in OSU Extension Facts No. 7150 and Oklahoma Alfalfa.
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| Richard Berberet,
Alfalfa Entomologist Department of Entomology and Plant Pathology Oklahoma State University |
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