Black Cutworm Moths Just Keep Coming

Black cutworm moth catches in many of our cooperator’s pheromone traps continue to be quite impressive (see “Black Cutworm Adult Pheromone Trap Report”). The timing of intensive moth captures, 9 or more moths caught over a 2-night period, over the past several weeks and subsequent larval development may challenge corn that is delayed in emergence or yet to be planted. This will be especially true for fields with abundant broadleaf weeds (esp. chickweed), if producers’ weed control activities are delayed or replanting is necessary because of low temperatures in the coming days (May 8-10).


Black cutworm larval instars 2 to 6, the 4th instar is left of the penny.

Black cutworm larval instars 2 to 6, the 4th instar is left of the penny.


Refer to the map, where we are tracking black cutworm development from the time of our first widespread intensive captures, April 8, to when we expect first significant damage. Based on the growth development model, it takes approximately 300 heat units (50˚F base) from egg hatch to early 4th instar; this is the life stage when black cutworm larvae begin to cut plants. Some leaf injury may be present before then, and this is an ideal time to treat – insecticides will be more efficacious than during the period when they have begun cutting plants. Using pheromone trapping of moths and tracking of heat unit accumulations for first cutting is not an exact science, but they do give us a good indication of when to better time scouting trips.

Because of the persistent cool temperatures this spring, black cutworm larval development has been delayed, as demonstrated in the accompanying map. Meaning, the many acres of corn planted the past weeks will likely “outpace” larval development. Of those fields yet to be worked and planted, the timing may coincide with larval development, thus threatening emerging corn. Since black cutworm has been a minor pest in recent years, producers may have a false sense of security with the seed-applied insecticides – which offer plant protection that is inconsistent, at best. Timely scouting and rescue treatments of foliar insecticides when necessary are the tried and true approach with this stand reducer. Happy scouting!


heat units (Base 50)

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