Western Bean Cutworm Flight Increases, Egg Hatch Is Underway

The western bean cutworm (WBC) trapping season continues, and after a slow start, moth flights have increased in many northern Indiana county traps this past week. With warm temperatures continuing, egg development and hatch will happen within about 6-8 days after they are first placed by females. This will give little time for egg scouting, and unfortunately larval scouting is more difficult, less reliable and time-consuming. In other words, some larvae have hatched and have already infested corn and for those just looking for egg masses beginning now, they will likely be underestimating the population.


Scouting pre-tassel corn for western bean cutworm egg masses.

Scouting pre-tassel corn for western bean cutworm egg masses.


However, it is not too late. This increased moth activity is likely the key period for egg-laying, as the vast majority of WBC eggs will be laid over the next 2 weeks. Use moth trap catches and recent field histories as your guide for prioritizing scouting areas – unlike armyworms and black cutworms, these moths don’t usually travel great distances before laying eggs. As you view the “Western Bean Cutworm Adult Pheromone Trap Report”, notice the variability of moth captures, even within close proximity of each other. Although the relationship between trap catches and damage is not particularly strong (i.e., high trap counts does not always mean high damage), traps are a good timing mechanism and presence/absence indicator. When they spike suddenly, it’s time to scout…for many that is right now, today.

Pre-tassel corn is preferred by egg-laying females. Research conducted at the University of Nebraska has shown that larvae survive best in late whorl stage corn. This is likely because this synchronizes their development with the onset of pollen shed, and pollen is a key, high-protein food source for young larvae before they move into corn ears.

Scouting should begin once moths are being captured each night. 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. Moths will lay eggs on whorl stage corn when pre-tassel/pollinating corn is not available. Larvae may initially be found in leaf axils, feeding on pollen that has accumulated there and can still be controlled with insecticides that reach down into these areas, but only for a short time. After this they move into the plant itself via the silks and are invulnerable after that. Remember that this pest is resistant to the Cry1F insecticidal trait – this is found in the vast majority of “traited corn” planted in the state. So scouting and timely insecticide applications where needed are a must for most producers in WBC’s zone of infestation, primarily the northern tier of counties in Indiana.




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