University of Illinois

No. 13/June 18, 1998

People in Southern Illinois Should Watch for the Other Corn Borer

Activity of southwestern corn borers has increased noticeably during the past couple of weeks. Ron Hines, senior research specialist at the Dixon Springs Agricultural Center, reported significant captures of southwestern corn borer moths from May 28 to June 6 in Pulaski and Massac counties. On June 11, Ron observed 35 to 40 percent whorl-feeding injury in corn that was 24 to 30 inches tall at the Dixon Springs Ag Center. He found an average of four first through third instars per plant.

We provided a detailed discussion of southwestern corn borers in issue no. 11 (June 5, 1998) of this Bulletin, so there is no need to repeat most of the information. However, you may encounter some confusing messages about economic thresholds for southwestern corn borers. Although most entomologists believe that economic infestations of these corn borers are uncommon, some have established 35 percent whorl-feeding injury as a static economic threshold. My gut instinct tells me that if the entomologists in Texas are not terribly concerned about first-generation southwestern corn borers, we need not be concerned either. However, growers in southern Illinois can judge for themselves.

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