2025 University of Minnesota Cooperative Black Cutworm Trapping Network
Report #2 April 5-April 11, 2025
This issue was prepared by:
Dr. Fei Yang – Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter
April 15, 2025
Greetings,
The network detected its first 2025 black cutworm moth arrivals last Thursday and Friday. Traps reporting low numbers of captures were scattered across southern Minnesota part of the state (Table 1). None of these captures were large enough to cause concern. An April 8th – 10th system could have brought black cutworm moths from their southern overwintering areas. We don’t have the data yet, but preliminary reports indicate more moth captures throughout the 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. The activity of the moths can be limited by cold nighttime temperatures here.
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.
Since insects are cold blooded, their activity and grow 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. Odd insect fact: If I remember correctly, there is at least one insect species (a Dermestid beetle) that can develop into progressively smaller rather than larger sizes, but this is believed related to food availability but not temperature.
In the next issue we’ll discuss how the pheromone trapping network and degree days can be used in black cutworm management.
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
