Late planting and a milder summer in many areas have impacted the spread of Western bean cutworm (WBC), but only in the sense of delaying the emergence of this destructive pest.
Recent trappings by university entomologists and field professionals from Pioneer Hi-Bred, a DuPont business, indicate the pest is moving eastward, with the heaviest infestations being reported in unprotected cornfields across northern Indiana, with some reports extending into Illinois and Ohio. Additional reports have confirmed the spread of WBC into central and northeastern areas of Michigan, areas new to WBC infestations.
"Traditionally, we’ve seen the heaviest pressure from Nebraska to central Iowa, but now we’re seeing WBC continue to move eastward along the I-80 corridor," says Paula Davis, Pioneer senior marketing manager for insect and disease control traits. "Most of the time the spread of WBC is complete by mid-August. This year it appears to be a little late, just like everything else."
WBC can reduce yields up to 40 percent in heavily infected fields. Young WBC larvae feed on tassels and silks, but eventually tunnel through the silk channel to reach developing kernels. Direct yield loss occurs as larvae consume all or parts of developing kernels. Because of the labor intensive nature of scouting, the critical timing needed for insecticide applications and the possibility that multiple treatments may be necessary, insecticides may not be an economical or effective solution to the WBC problem.
Spraying is occurring as signs of increased populations surface, but spraying must take place before the insect moves into the ear where it is protected by the husk.
The threshold is 5 percent of the plants with egg masses or small larvae in the tassel. With moth flights reaching peak levels and approaching completion, increased feeding can be expected.