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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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WINTER INFESTATIONS OF BLUE ALFALFA APHID |
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| The blue alfalfa aphid is not known to overwinter in Oklahoma. Infestations develop from winged adults that migrate from the south during February and March. Damaging populations typically occur in late winter and early spring, primarily during growth of the first crop of alfalfa. The amount of damage caused by this aphid is dependent on the growth stage of alfalfa when infestations begin. An additional factor that has resulted in increased damage to alfalfa since 1990 is the emergence of a virulent biotype (known as BAOK90). This biotype can cause severe damage to all alfalfa varieties that are grown in Oklahoma. When large numbers of blue aphids infest plants that are less than 6" tall, yield losses may approach 100% for the first crop and stand reduction of 60-80% may occur unless timely applications of insecticide are made. New fall plantings should be sampled by carefully brushing small plants so that aphids drop to the soil surface. When numbers exceed 10/plant, an insecticide application may be necessary to prevent death of plants and stand loss. When infestations occur during winter in established stands, sampling should be conducted by brushing crown growth to dislodge aphids, then carefully examining the soil surface beneath plants to estimate numbers. Spraying is warranted if numbers exceed 30/crown. Additional information on life cycles and control of aphids can be found in OSU Extension Facts #7150 and #7184. |
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| Richard Berberet, Alfalfa
Entomologist Department of Entomology and Plant Pathology Oklahoma State University  |
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