2026 University of Minnesota Cooperative Black Cutworm Trapping Network
Report #3 April 4-April 10, 2026
This issue was prepared by:
Dr. Fei Yang - Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter - Potter Bros., LLC
April 14, 2025
Greetings,
Traps reporting low numbers of captures were scattered across southern Minnesota part of the state (Table 1, Figure 1).
We are still using 8 moths/ 2 nights as a significant capture that indicates elevated risk for future high larval populations.
None of this week’s captures were large enough for great concern but the Murray County trap captured 6 moths.
Weather and moth migration have started to become more active since April 10th. We don’t have all the data yet, but preliminary reports indicate more moth captures this past weekend and early this week.
When trying to understand moth migration, remember that the winds aloft bearing migrating moths may be different than those on the ground and it doesn’t take long to get from south Texas to Minnesota at 50 miles/hour non-stop.
Degree days and black cutworm growth and development
The black cutworm life cycle, from egg to moth, takes 1½ months or more depending on temperature.
Insects are cold blooded, so their activity and growth rate depend on the temperature of their environment. Black cutworm moths are more active, and their eggs and larvae develop faster as temperatures warm. Insect development doesn’t occur below a base temperature or above an upper development threshold. Just like predicting corn growth with degree day accumulations (a.k.a. growing degree, heat units, growing degree days), degree days can be used to predict the stage of development for cutworm eggs, larvae, or pupae.
There are several ways to calculate degree-days for insect development, but fortunately, for our purposes, a simple max/min average model works well enough for black cutworms. Conveniently, we can use a 50°F lower developmental threshold for both corn and black cutworms.
A daily degree day accumulation = [ (Maximum temperature + Minimum temperature) / 2] - developmental threshold temperature. For an example of calculating degree day accumulations: The daily high was 70°F and the daily low was 52°F. The degree day accumulation would be: [(70+52) / 2] – 50 = 11 degree-days. To estimate the development stage, the daily degree day accumulations are then summed over the days of interest. Although there may be no insect growth and development on cold days, degree days are not negative. When the daily low temperature is less than 50o F use 50o.
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