2024 Iowa Moth Trapping Network Update: Week 4

May 1, 2024 9:46 AM
Blog Post

Last week (April 21 to April 27) had a few windy days that likely brought many moths into Iowa, but numbers were lower than Week 3. A total of 109 BCW moths were reported by our cooperators during Week 4. Most of those moths were reported between April 23 and April 25. Six significant flights occurred last week, adding to the numerous significant flights that have already occurred during the first month of moth trapping:

  • April 23 – Floyd County
  • April 24 – Benton County
  • April 25 – Benton County, Buena Vista County, O’Brien County, and Iowa County

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 April 21 to April 27
Figure 1. Black cutworm moth captures from April 21 to April 27. 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 1, 2024.

Maximum 2-night count of BCW April 21 to April 27
Figure 2. Maximum two-night moth captures in each county during Week 4 (April 21 to April 27). 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 will predict cutting dates across the state by mid-May and share them on ICM News, so make sure you are subscribed! In the meantime, you can see predicted cutting dates for counties withs significant flights here.

Follow the links to see reports from Week 1, Week 2, and Week 3. You can also track moth flights, black cutworm significant flights, and projected cutting dates for Iowa, Illinois, and Wisconsin at 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 ...