Damage from small caterpillars have been detected, so prepare to scout fields in the near future.
Black cutworm populations appear more active than usual this spring. As we have reported in previous weeks, Penn State Extension’s Black Cutworm Monitoring Network has detected several significant flights of this migratory pest species. We are now up to eight sites receiving enough moths to trigger degree-day tracking, and current degree-day accumulations range from 55 to 184 depending on locations across the state (Table 1).
Table 1
Degree-day accumulations through 16 May 2016 in eight regions in Pennsylvania that experienced significant flights of black cutworm moths. When 300 degree days accumulate at each site from the day of the flights, cutting damage can be expected to be evident in fields—this is when scouting should occur.
| County | Closest town | Accumulated degree days |
|---|
| Berks | Kutztown | 70 |
| Centre | Rebersburg | 69 |
| Clinton | Loganton | 58 |
| Elk | St. Mary | 55 |
| Franklin | Fayetteville | 184 |
| Lebanon | Cornwall | 114 |
| Lycoming | Montoursville | 120 |
| Potter | Ulysses | 85
|
At this point, black cutworm caterpillars are young (likely second or third instar) and feed at night, making small holes in leaves or removing tissue from the margin (Figure 1). If this damage is widespread, it is concerning in its own right, and may warrant an insecticide application. But this is early damage, is also a local indicator of a good-sized population that has the chance of causing damage when the caterpillar reach their fourth instar at 300 degree days.
After 300 degree days accumulate, producers should begin to scout fields for cutting damage. Because caterpillar populations are notoriously spotty, I would not recommend using the elevated risk as a justification for adding insecticide to a tank mix unless you have confirmed that damage exceeds the economic threshold. Insecticide applications not targeted and timed appropriately will not be effective, and will probably waste money. While some Bt varieties can be helpful for managing black cutworm, seed treatments are not very effective. Rescue treatments are usually the most efficient and economical tactic for managing black cutworm. For more information, see our black cutworm factsheet.
Figure 1
Damage in a Lancaster County corn field from young black cutworm caterpillars. Before caterpillars are old enough to cut, they can cause this sort of tunneling through young plants or even feed from the margins.