Migrating black cutworm moths found their way into southern MN this past week (April 20-26). In many cases, the number of moths captured indicate increased risk of black cutworm damage to susceptible crops planted into fields attractive to egg-laying moths.

The colorful map (Figure 1) shows some impressive captures by Minnesota standards. Larger, single night reports came from Olmstead (14 moths), Steele (11 moths) and Meeker (10 moths) Counties. Several other counties had significant 2-night capture totals of eight or more moths over a 2-night period (other red counties).

Remember that negative captures in a county do not mean there are no black cutworm moths. Like rainfall, the deposition of immigrating moths is not uniform across the landscape and traps are not located in equally attractive landscapes. Often, one trap in a county can catch numerous moths while another trap, just a few miles away, may capture none.

How do freezing temperatures affect black cutworm?

Early-instar black cutworm larvae, pupae and adults are very susceptible to temperatures below freezing. Large larvae can survive freezing temperatures, but only for short periods. This lack of cold tolerance is why black cutworms cannot winter much further north than southern Missouri. Black cutworm eggs are the stage most tolerant of freezing – they’re able to withstand temperatures at or somewhat below freezing for short periods. Therefore, even in those areas of Minnesota that saw snow last weekend, eggs near the soil surface are likely to have survived. 

Predicting black cutworm development

We use degree-days to predict cutworm development to better time scouting and, where needed, control. Depending on temperature, the eggs laid by moths from this flight will being hatching around May 5 and the cutworms large enough to cut small corn plants around May 25. 

To see the full report and cutworm development predictions for several locations in the state, visit UMN Cooperative Black Cutworm Trapping Network Report #3.

For more information, visit Black Cutworms or UMN Extension - Black Cutworm