2026 University of Minnesota Cooperative Black Cutworm Trapping Network
Report #2 March 17 – April 3, 2026
This issue was prepared by:
Dr. Fei Yang – Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter – Potter Bros., LLC
April 8, 2026
Greetings,
Black cutworms
Cold weather and a lack of the proper weather systems limited migration of moths into MN. A single moth was captured in an Olmsted County trap on March 26.
What conditions are needed for crop-threatening black cutworm (and armyworm) populations in Minnesota?
Migrating moth populations in overwintering areas. Black cutworms (Agrotis ipsilon) and armyworms (Mythimna unipuncta) cannot survive our northern winters but can survive and and reproduce as far north as topsoil remains unfrozen. Unusually cold winters can limit these populations.
Weather conditions to aid migration north when moths are ready to migrate. From late March through May, look for a cool, dry low-pressure system in western plains meeting a high-pressure system to the east bringing warm, moist Gulf air. The rotation produced by the two systems’ interaction creates strong southerly flows. These “low-level jet streams” are especially strong at night with migrating moths flying upward to meet them. The moths riding these systems often fall out with rain on the back side of thunderstorms passing through Minnesota.
The arriving moths find good sites to lay eggs and spring weather conducive for egg and larval survival. Moths, larvae, and to a lesser extent eggs, cannot survive freezing weather. Female black cutworm moths prefer low laying areas with winter annuals (e.g. shepherd’s purse) or early emerging annual (e.g. common lambsquarters) weeds. Armyworm moths are attracted to vigorously growing dense grasses (e.g. pastures, weeds, winter cereal crops) to lay eggs.
What do the black cutworm and armyworm pheromone traps capture and measure?
Unmated, female moths mate on arrival. Only male moths, attracted to a species-specific synthetic pheromone that mimics that produced by the female are captured by these traps. The pheromone traps are only effective for the few nights unmated migrant males are active.
The pheromone trap captures provide information on when, and where, moths arrive and estimate the size of the migration event(s). This information can be used to predict where, and using degree-days, when crop-threatening infestations can occur.
Unlike the pheromone traps, blacklight insect traps collect both sexes for as long as the moths live. They may capture larger numbers of moths over a longer period. Blacklight trap captures have not been correlated with the risk of black cutworm larva outbreaks, but they may be more predictive than pheromone traps for armyworms. Differences in biology of the two may explain the differences.
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.
One of spring’s visible signs of insect migration from the south is the arrival of red admiral and painted lady butterflies.
There is the possibility that a system is setting up that will create wind flows bringing strong southerly winds and gulf moisture as far as SE Minnesota this weekend. For those who have not set out their cutworm traps yet, please do so. Northernmost locations might want to delay until things start to green up although black cutworm moths can cue in on topography and weeds that are beginning to emerge.
Armyworms
For those trapping armyworms in the southern 2/3 of Minnesota, it would be good to place those by this Friday. Placing the trap near winter rye or dense grasses may help increase trap captures. Historically we often see the first arrivals in southern Minnesota in late April and early May.
For more information: bcw-reporting
This network is supported, in part, by the farm families of Minnesota and their corn check-off investment.
Products are mentioned for illustrative purposes only. Their inclusion does not mean endorsement and their absence does not imply disapproval.
Contact me with any questions, and Happy trails,
Bruce Potter
[email protected]
(507) 276-1184