Update: Check for Southwestern Corn Borer

ImageSouthwestern corn borer larvae.

Southern counties across central and southwest Kansas are reporting high numbers of southwestern corn borer egg masses and are treating those fields now.

First-generation infestations begin in late June and consist of dark-spotted white worms that feed for five to 10 days on leaf tissue in the plant whorl, then move downward to begin tunneling within the stalk. The second (and most damaging) generation occurs in August. Adult moths begin emerging and laying eggs starting around July 15 to July 23, with egg-laying reaching a peak somewhere between Aug. 1 to Aug. 15. The exact time of the beginning and peak of egg-laying is influenced by weather and geographic location. Eggs are deposited on leaves primarily in the ear region. Newly hatched larvae begin feeding on leaves, but prefer to feed on ear shoots, husks, and silks. Within 10 to 12 days, this generation also begins tunneling within the stalk, generally below the ear zone.

     Insecticide applications should be considered on susceptible corn hybrids when 20 to 25 percent of the plants are infested with eggs or newly hatched larvae. Most corn was planted late in Kansas due to the late cold weather, so these fields could become heavily infested. Lodging, caused by girdling of stalk by the larvae, can be avoided if the corn is harvested before girdling begins. However in late planted fields, this is harder to achieve unless the corn is used for silage.

g07111art01SW Corn borer moth and larvae (Photo by Armon Keaster)

Eggs of the second generation are deposited at the ear zone or a node above or below the ear. A female moth is capable of laying 100 to 400 eggs in her short lifespan (approximately 5 days).

SWCB-whiteeggs1-Web SWCB-CCEggs-Web

Eggs are initially creamy white but develop three red transverse bars within 36 hours of being laid, and these bars remain until the larva’s emergence (approximately 5 days). (photos courtesy of Univ. of TN, Inst of Ag.)

NOTE: Corn hybrids containing European corn borer targeted Bt toxin should control both Southwestern and European corn borers, however, research suggests some Bt types are less effective for Southwestern corn borer control, therefore scouting fields that contain these Bt genes is important as well. K-state Efficacy trials in the past have shown that varieties in the Yieldgard family and Herculex family (see handy Bt table link below) work well for the second generation of SW corn borers, but may not provide 100% protection for the first generation. Since there are many new Bt products targeting moth larvae (Lepidopteran-above ground Bt) available today, K-State efficacy trials will begin in 2014 to evaluate the current hybrids.


Check this Handy BT Table to see if your corn variety controls for corn borers.


For addition information and control options for Kansas visit:


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