2026 University of Minnesota Cooperative Black Cutworm Trapping Network
Report #4 April 11-April 17, 2026
This issue was prepared by:
Dr. Fei Yang - Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter
Greetings,
Based on weather forecasts, increased moth migration into Minnesota was anticipated for the April 11 – 17 trapping period. Strong southerly winds and associated storm systems led to many trap sites capturing black cutworm moths. Three locations had significant captures (Table 1, Figure 1). Traps checked April 12 and 13 showed the largest captures.
SE MN experienced storms with heavy hail and some tornadoes. Any moths caught in strong updrafts within hail and tornado events may not survive.
In the animated GIF file, you can see captures over the week.
These daily maps illustrate the variability of moth arrival and captures based on trap location and weather.
Eggs laid by female moths arriving with these early flights are likely to begin hatching later this week. Based on projected temperatures, the resulting black cutworm larvae will be large enough to start cutting corn about the 3rd week of May.
Some cooperators are also trapping armyworm moths. Additionally, low numbers of true armyworm moths arrived last week. Two trap sites in Olmsted County as well as traps in Dakota, Waseca, Martin Counties caught low numbers of armyworm moths April 12-16. I suspect armyworm moth arrivals will increase over the next few weeks. Black light traps, if operating by early May, are also very helpful in identifying crop-threatening armyworm arrivals.
Predicting outbreaks from migratory moths
In the last issue we discussed how degree-days can be used to estimate the development of insects and crops. How do you know when to start calculating the degree day accumulations? In the case of an annual crop such as corn, planting date is a convenient starting point. In the case of black cutworms, the pheromone trap network can help determine when to start degree days based on moth arrival. This date is used as a starting point or “biofix”. Rather than use the capture of a single black cutworm moth, the MN network uses a cumulative capture of eight moths over two nights as the biofix indicating a large migration event and an associated increased risk of cutworm injury to corn, soybeans, sugarbeets and other crops. These “significant events” are used as biofixes to calculate degree days for cutworm development models.
We can use base 50oF degree days to predict when black cutworm eggs will hatch (90 DD), when larvae will reach the fourth larval stage (instar) and large enough to cut small corn (312 DD), and when larvae will stop feeding and pupate (641 DD).
The degree day model often overpredicts development as soil moisture, residue, soil texture, and topography affect temperature near the soil surface where black cutworm larvae reside. These temperature effects, as well as multiple moth arrivals and a prolonged egg-laying period sometimes leads to a range of cutworm larval sizes present in the field.
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