Report #7 May 10-16, 2025
This issue was prepared by:
Dr. Fei Yang – Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter – Potter Bros., LLC
May 20, 2025
Greetings,
Black cutworms
No significant captures were reported in week 7 (Table 1, Figure 1). Black cutworm trapping will wind down on May 24 although some trappers may continue for a bit longer based on the agronomic situations in their areas.
Warm temperatures led to predicted development of black cutworm larvae faster by two or three days. Scouting for leaf feeding and possibly cutting of small corn should be underway in high-risk fields. The recent cool temperatures will slow the development of both corn and soybeans.
Larvae from the earliest mid-April moth arrivals may be able to cut small corn now. These larvae should cease feeding and being to pupate in mid-June (Table 2).
This is now a race in development stage between cutworm larva and corn stage. Remember, corn plants that are 5 leaves and less are most susceptible to being killed by 4th stage and larger larvae feeding below the growing point.
Armyworms
There were still no large captures of armyworm moths this week. Steele County had the only notable capture trap capture so far this spring (12 moths on April 22). The Polk County trap sites indicate that both black cutworms and armyworms have both made their way into NW Minnesota. Historically, most armyworms issues in Minnesota occur in late June and early July so there is still time for problematic moth flights to arrive.
Other cutworm species that can cause problems in Minnesota.
Black cutworms are not the only cutworm species that can injure crops in Minnesota. As corn (and other row crops) germinate and begin to emerge they can be attacked by several species of cutworms. Table 3 lists some of the species and their biology that might be found in Minnesota fields.
Most species overwinter in Minnesota as eggs or larvae. Black and variegated cutworms cannot winter here and migrate into the state each spring. We can project cutting dates for the black cutworms, but corn should be scouted for other cutworm species as soon as it emerges.
Because cutworms that overwinter, particularly those that winter as larvae, begin development before migrant black cutworms arrive, they are ready to feed on corn early. Often, the first corn leaf feeding observed in the spring is from overwintered dingy cutworm larvae. Dingy cutworms are commonly found in corn, but unlike black cutworms are seldom a threat. With a bit of practice, the two species are easily distinguished by the size of paired black bumps (tubercles) on the upper edges of each segment. These tubercles are unequal in size on the black cutworm. Dingy cutworms are often abundant when corn is planted after alfalfa or fields that were weedy the previous year.
Most cutworm species have prefer particular types of habitat. For example, sandhill cutworms are found in sandy soils and several species tend to be problems when crops are planted into sod.
Species identification is important to determine damage potential. Small larvae of all species feed on weeds and leaves and cannot cut corn. In addition to dingy cutworms, redbacked, spotted, and variegated cutworms are primarily leaf feeders feeding at or above the soil surface. Consequently, these climbing cutworms don’t usually cut corn below the soil line and growing point and the plant recovers. However, the larvae of some cutworm species (e.g., glassy, sandhill, darksided, claybacked and black) tend to feed below ground, at or below the growing point. This potential for feeding to kill corn plants makes black cutworm a threat. When larger larvae tunnel into the growing point, corn as large as 5 or 6 leaves can be killed. Fortunately, damaging black cutworm populations are infrequently encountered.
In the next issue we’ll wrap up the black cutworm trapping for 2025.
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