Report #3 April 12- April 18, 2025
This issue was prepared by:
Dr. Fei Yang – Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter – Potter Bros., LLC
April 22, 2025
Greetings,
Several significant black cutworm influx events occurred last week. Moths were captured by multiple traps throughout the week with the greatest activity Thursday and Friday (Table 1). Of particular concern are significant captures in Le Sueur, Waseca, Steele and Olmsted Counties. Some of these captures were quite large. An Olmsted County trap captured 18 moths, and a Steele County trap captured 12 moths April 17-18 (Table 2).
Using degree day models and on historical temperatures averages, larvae from this week’s flights should begin hatching during the first week of May and be large enough to cut small corn plants by the last week of May (Table 2).
Figure 1 shows the area of southern Minnesota where we know that large numbers of moths arrived. Remember, migrating moths do not arrive evenly across the landscape. Some trap locations may be better positioned to attract arriving moths. Other locations, if they experienced similar weather patterns, may have also seen large numbers of moth arrive last week.
Early reports indicate continued trap captures have continued this week. The system that brought thunder and some rain last night appears to have brought significant numbers of both black cutworm and armyworm moths.
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. When do the degree day accumulations? In the case of an annual crop such as corn, if soil moisture is adequate for germination, 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 cooperative black cutworm network uses eight moths over two nights as the biofix to indicate a large migration event and there is 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 the base 50°f 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 delays between moth arrival and a prolonged egg-laying period can sometimes lead to a range of cutworm larval sizes present in the field.
In the next issue we’ll discuss more ways to make scouting efforts more efficient. In the meantime, remember to record the tillage, planting, and cover crop termination dates for your fields.
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
