Report #5 April 26- May 5, 2025
This issue was prepared by:
Dr. Fei Yang – Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter – Potter Bros., LLC
May 6, 2025
Greetings,
There were several significant captures, mostly into the east portion of the network, April 28-29 last week. These were in Central (Wright), SC (Freeborn, Martin, and Steele) and SE (Olmsted), Minnesota. Early in the week, the Dodge County site was also significant with 10 moths SE Minnesota site captured April 25 and 26 (Table 1, 2).
Larvae from mid-April flights are still projected to reach 4th instar and large enough to cut small corn the last week of May (Table 2).
Figure 1 shows the areas where we know that large numbers of moths arrived last week. Based on a weekend road trip, field work is behind in some of these areas.
Scouting for leaf feeding from earlier April flights should begin around May 11th for corn. The warm weather in the forecast will speed both cutworm and crop development.
Armyworms
Several sites across Southern Minnesota reported captures, but all were low numbers. Some of the blacklight light traps should begin soon and that will improve the coverage for armyworm flights.
Managing black cutworm problems: Finding potential yield problems
A significant black cutworm pheromone trap capture does not guarantee larvae will be established in your fields. Scouting is the only way to determine when you have a problem and ideally before yield reducing stand loss occurs. Report #4 described fields at highest risk of damage from black cutworm larvae. Scouting for cutworms is easily combined with evaluations of corn stands and weeds for herbicide selection and application timing.
The first signs of the feeding of small larvae Will be small holes or notches on the leaves of emerged corn or weeds. Sometimes, larvae will cut weeds before they move to corn. Any partially cut plants will wilt. In dry, windy weather, cut leaves or plants rapidly wilt, dry and may blow away to leave no sign except missing stand. Be wary when lambsquarters and ragweed patches, or oat cover crops in sugarbeets begin to disappear. Herbicide applications may encourage cutworms (and several other pests) to switch from feeding on weeds or cover crops to corn.
Once leaf feeding and missing or cut plants are found, it’s useful to find a few of the larvae. Because larger larvae tend to cut corn below the soil surface and growing point, black cutworms are more damaging to corn than some other species. For example, the dingy cutworm, a cutworm species, commonly found Minnesota corn, feeds at or above the soil surface. As a result, dingy cutworms typically do not cut corn below the growing point present a minimal threat to corn. Knowing the size and stage of Also, knowing the size of the black cutworm larvae present will help determine the potential for future damage.
Active at dark, cutworms are nocturnal. During the day, they hide under soil clods, crop residue and loose soil, typically at the boundary between dry and moist soil. The cutworms will likely be deeper when soils are dry. Carefully look under pieces of residue and soil clods and in soil cracks close to cut or injured plants. If you don’t find a cutworm near the base of an injured plant, look near a couple plants on either side in the row. Finding cutworms in high residue, cloddy or muddy conditions is especially difficult. With leaf feeding you are looking for very small larvae. If your initial search for cutworm larvae is unsuccessful, Move to another area with injured plants.
Don’t confuse headless, legless cranefly larvae cutworms. All cutworm species have a distinct head capsule and three pairs of true legs near the front with five pairs of fleshy abdominal prolegs at the back. The black cutworm has a greasy appearance with a skin that appears rough under magnification. It is one of the few species where the front and rear tubercles (raised round wart like black bumps) on the top edges of each abdominal segment are unequal sized, with the front pair much smaller than the rear pair (Figure 2). The age of a black cutworm larvae can be estimated by measuring the cutworm’s length and width of the head (Table 3).
Take stand counts in areas of the field with damage and note the percentage of plants with leaf feeding and percentage of plants cut. To help with your decision, you can flag areas of row within the field and return the next day to determine if feeding or stand loss is ongoing.
Cutworm infestations in small corn (3 leaf or less) require more aggressive management than large corn. Do not give up on scouting too early. Late-instar black cutworms can kill up to 6-collar corn by burrowing into the growing point.
In the next issue we’ll discuss economic thresholds in the management of black cutworm infestations and post emerge control. In the meantime, remember to record the tillage, planting, and cover crop termination dates for your fields.
For more information on migration, and other management facts of these two crop pests, see
Corn-pest-management/Black-cutworm-corn and
Corn-pest-management/armyworm.
For more information: bcw-reporting
This network is supported, in part, by the farm families of Minnesota and their corn check-off investment.
Contact me with any questions and Happy trails,
Bruce Potter
[email protected]
(507) 276-1184