Insect Update: Black Cutworm and Potato Leafhopper

Black Cutworm

As reported last week, it is time for farmers in southeastern Pennsylvania to scout for damage in their corn fields from black cutworm caterpillars. Penn State's Black Cutworm Monitoring Network detected significant flights of black cutworm moths in three counties: Lebanon, Lancaster, and Bedford. Based on degree-day accumulations at these sites (Table 1), it would be wise to search fields for cut corn plants in Lebanon and Lancaster Counties, and the southeastern portion of the state generally. Folks around Bedford do not appear to be at a heightened risk from cutworm damage until sometime during the first week of June. Continue scouting fields until corn plants reach the V5 growth stage, which rarely receives cutworm damage. See our fact sheet on black cutworm for more details.

^*As of 29 May 2025

Potato Leafhopper

We have also gotten reports that the first potato leafhopper migrants have arrived in some Pennsylvania alfalfa fields. Potato leafhopper feeding reduces both yield and quality (especially lower protein content) and can decrease stand longevity. If damaging populations develop, early harvest or insecticides are often the only control options. Harvesting alfalfa early can stop damage, but regrowth should be scouted to determine if the next cutting also develops damaging populations. To target potato leafhopper effectively, populations should be sampled with a sweep net and treatments applied when economic thresholds are reached. Scouting details and economic thresholds can be found in our potato leafhopper fact sheet.