Cutworm trap captures

Scouting. Black cutworms are light grey to black; with granular-appearing skin and four pairs of fleshy prolegs on the hind end . They can be confused with another insect that may be found in fields during spring, the dingy cutworm. However, there are some characteristics that can help to set species apart.
Black cutworms are best identified by the dark tubercles found along the middle of the back. On each body segment, the pair of tubercles closest to the head is about one third to one half the size of the pair nearest to the abdomen.
Certain fields may be at a higher risk for black cutworm damage than others. These fields include those that are poorly drained and low lying, those next to areas of natural vegetation, and those that are weedy or have reduced tillage. Black cutworm may be more troublesome in fields where corn is planted late as plants are smaller and more vulnerable to damage. Also, if high numbers of larvae exist in a corn field, they may cause problems despite the use of Bt hybrids.

Description and Life Cycle
Fields should be scouted for larvae weekly until the corn reaches V5 by examining 50 corn plants in five areas in each field. Look for plants with wilting, leaf discoloration and damage, or missing plants. Note areas with suspected damage (with a flag) and return later to assess further damage. Larvae can be found by carefully excavating the soil around a damaged plant.

Figure 3. Black cutworm larval damage usually starts above the soil surface. Larvae are capable of clipping young corn plants. Photos by Steph Marlay.
Thresholds. If larvae found in the field are smaller than three-fourths inch, then a threshold of 2 to 3 percent wilted or cut plants indicates an insecticide application is warranted. If larvae are longer than three-fourths inch, the threshold increases to 5 percent cut plants. Remember to take into consideration the plant population in a particular field and adjust threshold numbers accordingly. However, with corn price and input fluctuations, a dynamic threshold may be more useful.

Preventative black cutworm insecticide treatments applied as a tank-mix with herbicides are of questionable worth. Black cutworm is a sporadic pest and therefore every field should be scouted to determine the presence of the insect prior to spraying insecticides.
Biology. Adult moths migrate on the wind from southern states near the start of spring, then mate and lay eggs. Around 1,300 eggs are laid by a single mated adult female. Eggs are laid in crop stubble, low spots in the field and in weedy areas. Younger larvae injure corn plants by feeding on leaf tissue and older larvae can cut seedlings.