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Western bean cutworm now emerging in corn PDF Print E-mail
Written by Assefa Gebre-Amlak   

Western bean cutworm moths have begun to emerge in most parts of northeastern Colorado. Historic data of moth flight show that the moth will continue to fly between mid-July and early August in Colorado (

Eggs are deposited in clusters on the top surface of leaves. Following hatch, young western bean cutworm larvae move to one of two places on the corn plant, depending on the stage of development.

If the plant has not tasseled, larvae will feed on pollen in the developing tassel. If the corn has tasseled, larvae will feed on silk in the ear. Once the ear is formed, the larvae will feed on developing kernels.

Control is expected with only those Bt corn hybrids containing the Herculex I or Herculex Xtra events. For corn hybrids that do not contain these events, fields should be scouted for this pest the next three weeks. Good control will be difficult once the larvae move into ears.

Chemical control is justifiable if 8 percent or more of the plants have egg masses or small larvae in the tassels and the crop is at least 95 percent tasseled. If tasseling is much less than this, the economic threshold should be raised as fewer larvae are likely to reach the ears.


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Holyoke Enterprise July 31, 2014