2026 University of Minnesota Cooperative Black Cutworm Trapping Network
Report #6 April 25- May1, 2026
This report was prepared May 5, 2026
Dr. Fei Yang - Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter
Greetings,
Black Cutworm
Moths continue to arrive in Minnesota. Although most traps capturing no moths or low numbers, three traps had significant captures. Traps were most active April 26-28. An eastern Redwood County trap had 9 moths April 24-25, Nicollet County captured 25 moths April 26-27, and Dakota County captured 16 moths April 27-29. (Table 1, Figure 1).
In addition to a general max/min temperature model for corn degree days, ag-climate-dashboard-tools has temperature dependent development models for several pests, including black cutworm.
The link to the Wisconsin site has more accurate models for development but does not allow forecasts of future temperatures like the corn model.
Cool weather has slowed both crop and cutworm development. Eggs laid from April 12-14 flights have started hatching. Based on projected temperatures, black cutworm larvae from early flights will be large enough to start cutting corn as early as May 22 (Table 2).
There are multiple generations of black cutworm produced each year in Minnesota, but this project focuses on the immigrant moths as they pose the greatest risk to row crops.
Armyworm
The Houston County trap continued to capture armyworm moths, but at lower levels than reported last week. An eastern Redwood County trap captured 18 moths April 27. Other widespread traps (Dakota, Freeborn, LeSueur, Martin, Polk, and Steele) with lower numbers indicate continued movement into Minnesota. Scouting high risk areas will be important. Economic infestations, if they develop, will likely be highly localized as is typical for armyworm infestations. There are two to three generations of armyworm in Minnesota depending on when moths arrive, and local weather. Economic outbreaks within Minnesota often occur in late June to early July.
Managing black cutworm and armyworm: Finding potential yield loss problems
Black cutworm (adapted from: Corn-pest-management/black-cutworm-corn)
A significant black cutworm pheromone trap capture does not guarantee larvae will be established in nearby fields. Scouting is the only way to determine when you have a problem and ideally, before yield reducing stand loss occurs. 2026 Report #5 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 oats 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 soil is 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.
Armyworm (adapted from: corn-pest-management/armyworm)
While both black light and pheromone traps can indicate when a moth flight has occurred and perhaps the relative size of the flight, it does not necessarily indicate where an armyworm infestation will occur. Scouting for larvae remains the best way to determine the risk of armyworm damage to a crop. In a year when armyworm larvae are abundant, finding the first economically threatening armyworm populations early can help encourage scouting efforts and prevent armyworm defoliated fields. Unlike scouting black cutworms, finding an armyworm infestation is best done by finding larvae before obvious crop injury.
The larvae typically pass through six larval stages (instars). Pale and tiny, the first- and second-instar armyworm larvae are difficult to find and identify. The 3rd and later instar caterpillars can range from tan and olive to nearly black in color. The pattern of a longitudinal dark band flanked by white-bordered pink to orange bands along the side is a distinguishing characteristic, as is the net-like pattern on the head and a dark band at the base of the abdominal prolegs (Figure 3).
A larva’s length and head capsule width can be used to estimate its age. Approximate larval sizes from a one population are shown in Table 4, although larval size can be highly variable based on temperature and available food.
Full-grown larvae are approximately 1 3/8 inches long. Multiple or extended egg laying and the varied microclimates within the field can lead to a wide range in larval development (Figure 4).
Developmental stages can be roughly predicted using a degree-day (DD) model with a base temperature of 50°F. It requires approximately 340 DD to reach the end of larval feeding and 575 DD to complete one life cycle from egg to adult.
The average duration of each life stage is shown in Table 5. Armyworm larvae are voracious feeders. Note how most foliage is consumed by the last instar. The presence of the insect and its feeding often go unnoticed until large populations defoliate a field or pasture overnight.
The late second instar and older larvae chew holes and notches through the leaf from the edge of the leaf blade toward the midrib and may feed anywhere on the plant.
Older larvae avoid light, hiding during the day in stubble, under leaves or soil clumps near the base of the plant, or in
the whorls of larger corn. Large larvae are often found on the ground and under lodged small grains and grasses.
From dusk to dawn, and on dreary, cloudy days, the larvae will move higher on the plant to feed. Third to sixth-instar
larvae curl into a C-shape when disturbed.
Armyworm outbreaks are often worse in cool, wet conditions. This may reflect optimal temperatures for the insect, but those same environmental conditions also favor lush dense growth of small grains and cool-season forage grasses. It may also reflect multiple weather systems bringing moisture and insects from the south.
Lush grasses are preferred egg laying sites for the armyworm moth. lodged areas of small grains, grasses or the grass borders of corn and small grain fields should receive special attention when scouting. Fields with late terminated cover crops should also receive scouting efforts. When they have defoliated an area, larvae will move from field borders or between fields.
Armyworm larvae are most active at night and on cloudy days. During the heat and bright sunlight of day, larvae often hide under leaf litter or soil clods on the ground and scouting is often more effective near dawn and dusk and on cloudy days. When disturbed, armyworms drop to the ground and curl into a C-shape to “play possum”. Fecal pellets are a sign that an infestation has occurred, but the presence of live larvae indicates it is ongoing.
Preliminary scouting for armyworms in small grains, field edges, forage grasses, and even grassy areas within row crops can be done most effectively with a insect sweep net.
Once armyworms are found, switch to a crop appropriate scouting method to assess crop risk.
In the next issue we’ll discuss economic thresholds in the management of black cutworm and
armyworm infestations and post emerge control.
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
This and previous reports can be found at 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