Black cutworm moths arrive in Iowa with spring storms and lay eggs in and around fields. Emerging BCW larvae feed on winter annual weeds, cover crops and seedlings. The larvae will cut seedling corn as they mature. When scouting for BCW caterpillars it is based on degree days after their peak flight of the moth occurs. A peak fight is defined as capturing eight or more moths over a two-night period.
As the degree days’ approach 300, keep a close eye on the map as you will want to be scouting a few days before the actual 300 scouting threshold in case your field has had slightly different temperatures than the reporting stations.
Scouting
When out scouting for BCW look in fields that are poorly drained, low lying or weedy fields, as well as those next to a natural vegetation or with reduced tillage, as these fields have higher risk of BCW injury. Cornfields with a poorly killed cover crops might attract the egg laying females as well as late planted corn fields.
Fields should be scouted around the V5 stage. Examine 50 corn plants in five different areas in each field for wilting, leaf discoloration and damage or plants that are missing or cut. Flag these areas so you can return to them at a later date to see if further injury has occurred. Larvae can be hard to locate.
Identification
Black Cutworm are grainy, light grey to black skin and have four pairs of fleshy prologs on the end of their abdomen. There are pairs of dark tubercles, or bumps, along the side of the body. These tubercles are approximately 1/3 to 1/2 the size of the pair closest to the abdomen. BCW and Armyworm can be mistaken for one another.
Damage
BCW exhibit two types of feeding patterns depending upon the amount of moisture in the soil and size of the plant. When soil moisture is adequate and the plants are small the larvae will hide in the soil during the day and move to cut the plants just above the soil at night. One larvae can cut off up to 5 plants in their development. When the soil is drier, the larvae do not move to the surface to feed, instead, they will chew into the plant just below the soil surface. This causes the corn plants to wilt and usually dies.
Threshold
Common thresholds for seedlings, V2, V3, and V4 stage corn plants are 2, 3, 5, and 7 plants cut off out of 100 plants.
