2019 UMN Cooperative Black Cutworm Trapping Network Report #3

Report #3 Week of April 20-26, 2019

For more information: Black Cutworm Reporting Network

May 1, 2019

Greetings:

BCW moth captures April 20-26, 2019Figure 1. Maximum two consecutive night black cutworm captures reported by county (April 20-26).


Unfortunately, we have a colorful map this time (Figure 1).  Migrating black cutworm moths found their way into southern MN. 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.

Some of these captures were impressive by Minnesota standards. For example, some of the larger, single night reports include: Olmstead county traps with 14 moths, Steele County with 11 moths, Meeker County with 10 moths. Several other counties had significant 2-night capture totals of eight or more moths over a 2-night period. Most of these moths appear to have arrived the nights of April 20-21. There may have been an additional April 23 immigration event but cool night temperatures may also have reduced moth activity, delaying mating and pheromone trap captures of males.

It is important to 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.

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. 

To simplify the math on my end, I will use April 22 for the date to begin calculating degree-days for larval development and corn damage for all of the April 20-26 significant captures (Table 1).  Based on the forecast temperatures for this spring, actual development is likely less. Additionally, as the season progresses, predictions for locations will diverge based on local weather.

estimated development of black cutworms based on captures

Table 1. Estimated black cutworm development for significant moth captures. Current and forecast degree-days are generated from the U2U Corn Growing Degree -Day application at the Midwest Regional Climate Center https://mrcc.illinois.edu/U2U/gdd/.

Particularly in those areas that saw higher moth captures, fields without spring tillage may have been attractive to egg laying moths and will bear extra effort when scouting.

Next week we will discuss habitats most likely to see black cutworm damage and temperature dependent development. If you just can’t wait, see: Black Cutworms or UMN Extension - Black Cutworm

During the spring, results of the 2019 trap network captures and predictions of BCW cutting will be posted weekly at: https://z.umn.edu/bcw-reporting. There will be additional alerts for any BCW high-risk areas picked up by the network!

This project is supported, in part, by the farm families of Minnesota and their corn check-off investment.

Until next week,

Bruce Potter and Travis Vollmer