Western Bean Cutworm Moths Flying in Western Kansas

Western bean cutworms are primarily a pest of corn, with activity generally isolated to the western third of the state. This pest has a single generation and begins emerging towards the end of June and early July, generally near the time corn is tasseling. White egg masses are laid on the upper surfaces of the upper leaves, turning purple the closer they get to hatching (Figure 1). Once the eggs hatch, caterpillars will enter corn ears to feed on the developing kernels. After several weeks of feeding, mature caterpillars will exit the corn ears and enter the soil to overwinter in earthen cells.

Figure 1. Maturing western bean cutworm eggs.

Western bean cutworms began to emerge during the second week of June, and pheromone traps have detected them in several areas of western Kansas with a rapid increase in numbers during the last week of the month (Figure 2). These trap catches are not a metric for determining potential losses in corn, nor are they used to make treatment decisions, but they serve as an important tool to help detect when moths start to emerge from the soil. Knowing when moths are active allows for appropriately timed scouting efforts.

Figure 2. The total number of western bean cutworm moths caught in pheromone traps in June.

Scouting for eggs is the best approach for detecting western bean cutworm pressure in the field. Early detection of egg masses is important, as any chemical control needs to happen before caterpillars enter corn ears, where they will be protected from foliar sprays. Scouting should begin now in areas where moths have been detected and continue until all silks have turned brown. When the field is almost fully tasseled, an average of 6 to 8 % of plants with egg masses or small caterpillars justifies control measures. Control will be reduced if caterpillars have already entered the ear tips; frequent scouting is important.

For western bean cutworm control options, please see the 2026 Corn Insect Pest Management Guide:

https://bookstore.ksre.ksu.edu/item/corn-insect-pest-management-2026_MF810

Track weekly counts of fall armyworm by county during the 2026 season at the website below:

Great Lakes and Maritimes Pest Monitoring Network: https://experience.arcgis.com/experience/7164d23d488246d198dcf7a07d8c9021/page/Home?views=Moth-Counts

Monitoring western bean cutworm activity in 2026 would not be possible without the help of: Amanda Burnett (Greeley Co.), Jeanne Falk Jones (Thomas and Sherman Cos.), and Lauren Thompson (Thomas and Sherman Cos.).

 

Anthony Zukoff – Extension Entomology – Garden City
azukoff@ksu.edu