Late season black cutworm damage being seen
Damage from late season black cutworm is being seen in southwest and mid-Michigan corn, soybeans and dry beans.
2012 has certainly been an "interesting" year. The latest wrinkle in the growing season is late season black cutworm damage. In the southwest, later planted commercial corn has been the primary crop that has seen the challenge. In mid-Michigan, there have been reports of black cutworm feeding on dry beans and soybeans.
Usually, cutworms are a very early season pest of corn. They occasionally pose challenges to the bean crops. What is unusual right now is that we are seeing quite a few moderate-sized larvae in the fields, which means that there will be the potential for cutting damage to continue for a period of time. It is important to remember that these insects do not pose a threat to the larger corn plants, so corn that is V4 to V5 or above is not going to suffer feeding damage from the larvae.
Damage is primarily being found in southwest Michigan in Kalamazoo and St. Joseph counties on fields with organic soils or in areas adjacent to wetlands or field edges. Agronomist Jon Silsby reports that the patterns of impact are similar to what you might expect from armyworms, moving in from a field edge, but the damage is definitely cutworm. In visiting with Dan Rossman, Gratiot County MSU Extension, agri-businesses in mid-Michigan are reporting clipping in dry bean fields where there were weeds that were burned down later in the season and in no-till planted soybeans.
Regardless of the crop, the answer to protecting your fields is to scout for incidence of damage and the presence of larvae. You may have to look in about a 2-foot diameter around a cut plant to find the cutworm. They are primarily nocturnal or early morning feeders, and will move underground during the day.
Cutworm damage is so sporadic that it is critical to get out and look for fields that are experiencing feeding damage before making spraying decisions. Treatment thresholds in corn, soybeans and dry beans are 5 percent feeding damage and larvae below 1.5 inches in length. MSU Extension bulletin E-1582 can provide some guidance in selecting insecticide treatments for corn, soybeans and dry beans.
For more information on black cutworms, MSU field crops entomologist Chris DiFonzo wrote an informative article called How to bake a black cutworm cake that is full of excellent pictures and information.