University of Illinois

No. 18/July 23, 1998

Onslaught of Southwestern Corn Borer Adults Continues

Reports of captures of southwestern corn borer moths in traps in southern Illinois continue to be impressive. Observers are capturing almost 200 moths per night in some counties. Obviously, based on trap captures thus far, southwestern corn borers pose a much more considerable threat to corn in southern Illinois than do European corn borers. Producers south of I-64 need to keep a sharp eye focused on the development of this potentially devastating insect pest. Corn growers between I-64 and I-70 also need to keep their eyes open. Although most heavy infestations of southwestern corn borers are concentrated south of I-64, occasionally economic infestations occur a bit farther north.

Girdled stalk caused by southwestern corn borer.

In last week's Bulletin (issue no. 17, July 17, 1998), we published an article that included some details about second generation southwestern corn borers. Some of that information bears repeating.

"Summer" phase and "winter" phase of southwestern corn borer larvae.

Southwestern corn borers have two generations per year in southern Illinois. The second generation causes damage that is much more severe than damage caused by European corn borers. The larvae that will overwinter tunnel very low in the plant, girdling the stalk from within. Girdling greatly weakens the stalks, inevitably resulting in lodged corn.

For the second generation of southwestern corn borers, look for egg masses and larvae on the leaves or larvae behind the leaf sheaths. A treatment may be justified when 25 percent of the plants have eggs, or larvae in the whorls or behind leaf sheaths.

Insecticides labeled for control of second-generation southwestern corn borers include *Ambush 2E at 6.4 to 12.8 oz per acre; Lorsban 4E at 1.5 to 2 pt per acre; Lorsban 15G at 6.5 lb per acre; *Penncap-M at 2 to 4 pt per acre; *Pounce 1.5G at 6.7 to 13.3 lb per acre; *Pounce 3.2 EC at 4 to 8 oz per acre; and *Warrior 1EC at 2.56 to 3.84 oz per acre. The use of products preceded with an asterisk is restricted to certified applicators. Please follow all label directions and precautions.

Kevin Steffey (, Extension Entomology, (217)333-6652