As we move into the first days of summer, we are finished with the early season, migratory moths and caterpillars (armyworms, black cutworms) and are now into those that overwinter here. For those pheromone trapping for western bean cutworm moths, you should begin this week. This is just the beginning of an extended moth emergence and flight, with their peak activity expected 2-3 weeks from now. Those in high-risk areas, i.e., sandy soils, high moth flight and WBC history should be gearing up for field scouting of corn, even those with Bt-traits. Depending on the trait expressed by your corn hybrids, efficacy can be highly variable.
Scouting of pre-tassel corn should begin once multiple moths are being captured regularly. In five different areas of a field, inspect 20 consecutive plants for egg masses which are laid on the upper surface of the top leaves of corn and/or larvae that may have hatched and crawled to the whorl and begun to feed. Usually the newest, vertical leaf is the best place to look for egg masses. Young larvae need pollen to survive, and female moths are most attracted to cornfields that are just about to pollinate (pollen is the primary protein source for young larvae). However, moths will lay eggs on whorl stage corn when pre-tassel/pollinating corn is not available. After hatching, larvae immediately crawl down into leaf axils and the whorl for protection, and begin to feed on leaf tissue and any shed pollen they can find. Later damage from larvae, as they feed deep in the whorl (attacking the tassel to get at pollen), will resemble corn borer or fall armyworm damage. Initially the damage will be subtle and not economically important (or even noticeable). Later stage, large larvae enter the ear and feed on corn kernels and can cause economic damage, and also can exacerbate ear rots, including Gibberella ear rot.
Remember that WBC larvae are no longer susceptible to most of the Bt traits in our corn hybrids and therefore scouting, followed by timely insecticide sprays are really the only reliable control option for the vast majority of producers located where this insect is common, principally the northern tier of counties in Indiana, extending into Michigan and parts of Ohio. Only Bt hybrids expressing the Vip3a toxin will offer reliable control of this pest, so be sure to know what you have in your field and scout as needed. See this handy Bt Trait Table to check where your hybrids fit in terms of the pests managed.
There is still time to order materials and begin trapping for your operation! We order our supplies from Great Lakes IPM. Stay tuned for further news on Western Bean Cutworm as flight begins.
Equipment needed for western bean cutworm moth monitoring: universal (a.k.a., bucket) trap, pheromone lure, and a kill-strip
Two captured western bean cutworm moths at the bottom of the bucket trap next to the kill-strip
