2024 Iowa Moth Trapping Network Update: Week 7

May 22, 2024 9:44 AM
Blog Post

Black cutworm (BCW) moth flights seemed to wind down a bit during Week 7 (May 12 to May 18). Our cooperators recorded 106 BCW moths around the state. Only one significant flight (Buena Vista County, May 14) occurred during Week 7, which is a big change from previous weeks where several significant flights have been reported.

Continued significant flights mean that folks could see prolonged feeding by black cutworm in the field. This may be especially important for areas of the state that have not yet been planted or areas that need replanted due to recent rainfall. Remember that black cutworms that are 4th instars or larger can cut corn plants until the V5 growth stage, so continue to scout and determine if feeding warrants management.

Figure 1 shows where moth traps are established throughout Iowa and black cutworm trap captures by county. Figure 2 shows the maximum 2-night capture in each county. This is an important distinction because although total moth counts tell us a bit about moth activity in the region, we determine whether a significant flight has occurred based on total captures over two nights. The red coloration on both maps indicate significant flights occurred, but Figure 2 gives a better sense of where large flights occurred even if they were not significant.

BCW Counts May 12 to May 18 2024
Figure 1. Black cutworm moth captures from May 12 to May 18. The bold number indicates the total moth count for the week (for counties with multiple sites, only the site with the highest weekly moth count is reported; highlighted counties without numbers indicate that traps are placed but no reports have been received). The number in parenthesis represents the season-long total black cutworm captures in that county. Data is current as of May 22, 2024.

Maximum 2-night count of BCW May 12 to May 18 2024
Figure 2. Maximum two-night moth captures in each county during Week 7 (May 12 to May 18). Increasingly intense colors indicate more moths were captured over a two-night period during the week.

What is a significant flight? A significant flight of BCW occurs when 8 or more moths are captured over a two-night period; this serves as the “biofix” for degree-day accumulation and indicates an increased risk of black cutworm injury in corn. A degree-day model for black cutworm development predicts that larvae are large enough (4th instar or larger) to cut corn plants once 300 degree days (base 50°F) have accumulated since a significant flight occurred. I predicted first cutting dates for the state already, but additional significant flights could mean prolonged feeding by black cutworm in the field. I will continue to update predicted cutting dates for counties with significant flights here.

Follow the links to see reports from Week 1, Week 2, Week 3, Week 4, Week 5, and Week 6. You can also track moth flights, black cutworm significant flights, and projected cutting dates for Iowa, Illinois, and Wisconsin on https://corn.ipmpipe.org/insects/.

Surrounding states also monitor and report BCW and TAW captures. If you live near the state border, it may be beneficial to check these resources periodically. More resources may be available than what is listed here:


Ashley Dean Agriculture and Natural Resources Extension Specialist II

Ashley is an education extension specialist for field crop entomology at Iowa State University. She coordinates the Iowa Moth Trapping Network, the Regional Corn Rootworm Monitoring Network, and the Iowa Pest Alert Network. She also develops educational resources for field crop pests in Iowa and ...