Windy conditions last week (April 14 to April 20) brought a lot of black cutworm (BCW) moths into Iowa. A total of 157 BCW moths were reported by our cooperators during Week 3. April 17 had the most total moths reported (50 moths), but captures were consistent throughout the week. Ten significant flights occurred last week, and two sites had multiple significant flights during the week:
- April 14: Muscatine County
- April 15: Muscatine County, Benton County
- April 16: Muscatine County
- April 17: Benton County, Marshall County
- April 18: Muscatine County
- April 19: Benton County, Keokuk County, and O’Brien 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.
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 with significant flights here.
Follow the links to see reports from Week 1 and Week 2. 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 ...