Report #4 April 19- April 25, 2025
This issue was prepared by:
Dr. Fei Yang – Extension Corn Entomologist, University of Minnesota Department of Entomology
Bruce Potter – Potter Bros., LLC
April 29, 2025
Greetings,
More significant black cutworm events occurred last week. Moths were captured by most traps throughout the week with the greatest activity Monday and Friday (Table 1). Of particular concern are significant captures in Meeker, McLeod, Nicollet, Freeborn Martin, and Rock Counties. Most notable were McLeod County (12 moths April 19), Meeker (12 moths April 21), Martin County (10 moths April 25). The Rock County trap captured 18 moths on April 22 following a 6-moth, three-night capture on the 21st (Table 2).
Figure 1 shows the areas where we know that large numbers of moths arrived last week. Keep in mind that other areas may also have had large numbers of moth arrivals.
Note: I likely missed the emails in time for Chippewa (17 moths on April 15-16) and Renville3 (12 moths on April 17-18) to be included in the week 3 report. These captures expand last week’s areas of potential infestation to the west.
Eggs from these early flights should begin to hatch late the 1st week of May and five-leaf or less corn at the end of May would be susceptible to cutting by larvae (Table 2).
Early reports indicate large numbers of black cutworm moths continue to arrive. Yesterday’s storms might have brought quite a few along.
How to scout for black cutworms and armyworms more efficiently.
Both insects are hard to scout for as problems tend to be concentrated in particular fields and even portions of fields based on egg-laying habits of the moths and subsequent habitat suitability for the larvae.
How can we focus efforts on fields that are most likely to be infested by black cutworms?
1) Egg-laying females are attracted to untilled fields, particularly with soybean residue to lay eggs. Use tillage date and moth arrival dates (biofix) as a first step to prioritize fields for scouting.
2) Focus on fields with a history of winter annual weeds or early- emerging spring weeds that the egg-laying adults find attractive. Low lying areas are often attractive.
3) Use degree-day projections to time scouting before feeding by large larvae can cause significant stand loss. Initial feeding by black cutworm larvae causes small holes in the leaves of weeds, corn and other crops. When the larvae reach the fourth stage, they can cut off small corn. Stands of some stand density sensitive broadleaf crops such as small, seedling sugarbeets can be cut by cutworms less than 4th instar. As the scouting season progresses, focus on corn that is 5-leaf stage or less.
4) Corn Hybrids without above-ground Bt traits should be prioritized. Black cutworm larvae are controlled by Hybrids with the Vip3A or Cry1F proteins. To determine if the trait package in your hybrid controls black cutworm, download The Handy Bt Trait Table for US Corn Production reference.
Armyworm note:
Based on a Redwood County pheromone trap, armyworm moths began arriving on April 16. Most of these captures have been single moth captures. An exception was the capture of 12 moths in Steele County on April 22. This is a large capture for the pheromone traps we use, and it indicates potential for yield impacts from this species.
Early reports indicate large numbers of black cutworm moths continue to arrive. Yesterday’s storms are likely to have brought quite a few with them.
What about scouting armyworms?
1) Two to three after moths arrive, focus on your scouting efforts in fields and field borders with dense vigorously growing grasses. Lodged field border and cereal crops, portions of fields with dense, grass weeds, and late-terminated grass cover crops are attractive to egg-laying female armyworms.
2) Scout when grass cover crops are terminated. This is especially true for corn planted into rye cover crops.
3) A sweep net is helpful in locating infestations of small larvae.
4) Keep in mind, the potential for migration of “armies” of large larvae moving into crops when they deplete food sources.
5) Only corn hybrids with the Vip3a trait will effectively control armyworm larvae.
In the next issue we’ll discuss the management of black cutworm infestations. 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
