In Northern Pennsylvania, it is Time to Scout for Black Cutworm Damage in Corn

In late April and early May, Penn State's Black Cutworm Monitoring Network detected significant flights of black cutworm moths in five counties: Blair, Huntingdon, Lancaster Lebanon, and Potter counties. Two weeks ago, we reported that it was time for folks in southeastern and central Pennsylvania to scout for black cutworm damage in corn. Since significant flight were detected, all these areas have accumulated 300 degree-days (Table 1), so cutting damage by caterpillars should already be evident if it is going to occur.

By this weekend, the time to scout will have arrived for Potter County and the rest of the northern tier of counties (Table 1). While we only detected a significant flight in Potter County (Harrison Township), we had limited numbers of traps deployed so I recommend that corn growers in northern Pennsylvania take a conservative approach and begin scouting this week and continue to do so until corn plants reach the V5 growth stage, which rarely receives cutworm damage. While I recommend that folks start scouting, I understand that there is a lot of variation in corn development in northern counties with some at growth stage V4, while many acres have yet to be planted. Black cutworm can cut plants from V2 to V5, so scout strategically based on your situation.  It seems likely that the yet-to-be-planted fields will miss much of the risk from black cutworm.

While you are scouting, remember that risk from black cutworm damage depends on growth stage. Economic thresholds for black cutworm are 2, 3, 5, and 7 cut plants per 100 plants for seedling, V2, V3, and V4 stage plants, respectively. Finding this cutting damage (Figure 1) and applying rescue treatments if necessary is the most effective and economical way to control black cutworm populations. Only two Bt traits (the Cry1F protein, known as the Herculex 1 trait, and the Vip3a protein, known as Viptera) provide some control of black cutworm, and seed-applied insecticides provide little control, with at least one research study showing that seed-applied insecticide only provided 30% control. Tank mixes of pesticides that include insecticides are often unreliable because they are rarely applied at the right time for black cutworm control and can significantly set back natural-enemy populations, which can help control black cutworms. The best approach is scouting periodically and applying insecticides if cutting damage exceeds economic thresholds. See our fact sheet on black cutworm for more details.

^*As of 6 June 2024