Last week, we saw an increase in the number of moths caught around the state. This is not surprising considering a few storm systems moved through the Midwest, and strong southerly winds prevailed on April 23 and during the late part of last week. In total, our cooperators captured 105 true armyworm (TAW) moths and 136 black cutworm (BCW) moths during Week 5 (April 24 to April 30).
Week 5 report:
Moths of each species were captured each day last week. Of the 105 TAW moths, 51 were captured April 24-25 and 45 were captured April 29-30. This trend was similar for BCW. 58 BCW moths were captured April 24-25 and 68 were captured April 29-30. These spikes showed up right after we experienced southerly winds. Figures 1 and 2 show the Week 5 trap reports for true armyworm and black cutworm, respectively.
A few significant flights of BCW occurred during Week 5. Two significant flights occurred in Washington County (southeast) on April 29, and Marshall County (central) had a significant flight on April 24. In addition to these, we had a few potentially significant flights in Mahaska (southeast) and Washington (southeast) counties on April 24 and Lucas County (south-central) on April 29. I marked them as significant flights on the map because I will use them when predicting cutting dates but based on the number of days between trap reports it is unclear if they are significant flights or not (hence, potentially significant). Remember that the significant flight threshold is over a two-night period; if traps are not checked over the weekend or for more than a few days, it is a bit harder to tell exactly when those moths arrived, so we do the best we can.
Follow the links to see reports from Week 1, Week 2, Week 3, and Week 4. You can also track moth flights and black cutworm significant flights for Iowa, Illinois, and Wisconsin on https://corn.ipmpipe.org/insects/. In a few weeks, we will begin predicting cutting dates for Iowa, which will be posted on the corn IPMpipe website and ICM News.
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:
- University of Minnesota
- University of Missouri
- University of Illinois
- University of Nebraska-Lincoln
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!
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 ...