Don't Overlook This Early Pest

Photo from extension.entm.purdue.edu 

I realize that right now the number one thing on our minds is getting the crop planted, but it won’t be long until we need to start scouting for pest in those newly planted fields.  Black cutworms come early and love newly emerged corn plants.  They also can drastically reduce your corn populations if they go unnoticed for very long.

Because black cutworm moths are attracted to green vegetation for egg laying, infestations of larvae usually appear first in weedy areas of fields. Newly hatched larvae feed on weeds and young corn plants if present, leaving small irregular holes in the leaves. Such early feeding is of little significance to plants. However, larger larvae may notch the stems of seedlings immediately below the soil surface, which can cause plants to wilt and die. They may completely cut through stalks, which can result in severe stand reductions.

According to UK Extension Entomology Dr. Ric Bessin, the black cutworm is most serious in weedy, late-planted fields with poor drainage, especially during cool, wet springs. Eggs are laid singly or a few together on leaves or stems of weeds, crop residues, or bordering fields before the corn is planted. The young larvae feed on these plants until corn seedlings emerge. Small larvae feed at the surface and may chew on the edges of leaves, while older larvae feed entirely underground and tunnel into the plant. This cutworm tends to carry cut-off plant parts into its burrow which is likely to be in moist, firm soil. Burrows are three to four inches long.

Although three to four generations occur each year, it is the first one attacking seedling corn that is the most serious.

Larvae vary from dark greasy-gray to black. They have a lighter stripe down the middle of the back and a brown head capsule. The skin, roughened with blunt-convex granules, has a generally greasy appearance. Fully grown larvae reach 1-1/4 to 1-3/4 inches.

The adult black cutworm moth is reddish-brown with a front wing that is brown to black in the center two-thirds and clay-colored to the tip. There is a distinct black, “dagger-like” dash near the front margin of the front wing.

Early detection of economic infestations means that an insecticide can be applied before serious damage occurs. Careful scouting of corn fields is the most effective means of detecting economic infestations of cutworms. Scouting for cutworms should begin as soon as the corn emerges and continue twice weekly until the plants reach 18 inches high.

When scouting for economic infestations of cutworms, check in at least five areas of the field, examining 20 consecutive plants. Record the number of plants that are cut, wilted, or showing signs of leaf feeding. While walking through the field, observe the evenness of cutworm infestations. Look for live cutworms around freshly damaged plants. First, check under clods around the base of plants. Then, dig up an area three inches in radius and three inches deep around the plant. Record the number and average length of the live cutworms.  Treat when 3% of the stand is cut or 2 or more larvae are found per 100 plants.

Insecticides applied at planting time solely for cutworm control are not recommended. Any insecticide applied at planting may not provide acceptable control of heavy cutworm infestations, and a rescue treatment may be necessary anyway. In addition, preventive measures may not pay because damaging numbers of cutworms do not occur every year.

If cutworm rescue treatments are needed, insecticides such as Lorsban, Mustang Max and Warrior are labeled for such.  Be sure to read and follow the label of all pesticides carefully.

For more information on black cutworms and other insect management recommendations, contact the McLean County Cooperative Extension Office at (270)273-3690.  Educational programs of the University of Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.