Warm weather and strong winds during the second week of moth trapping pushed many moths northward into Iowa. During week 2 of the Iowa Moth Trapping Network (April 9 to April 15), our cooperators reported 95 black cutworm (BCW) and 46 true armyworm (TAW) moths around the state. Two significant flights of black cutworm occurred last week, as well as two potentially significant flights.
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!
Okay, so what is a “potentially” significant flight? Our cooperators are busy people, so they may not check the traps every day or over the weekend. That sometimes makes it tricky to determine if a significant flight occurred when 8 or more moths are captured in a short time span (over 3 or so days). It is entirely possible all of those moths moved into Iowa the same night or over two consecutive nights, but I will never know for sure. So, I just report those as “potentially significant,” that way we are on the more conservative side of scouting for black cutworm.
Week 2 report:
Most of the TAW moths were reported on April 15 (25 moths) and in Taylor and Mills counties in southwest Iowa. Over half of the BCW moths were reported during the first half of the week. There were two separate significant flights that occurred in Taylor County (April 11 and April 15), and there were potentially significant flights in Hancock County (April 10) and Mahaska County (April 12). Figures 1 and 2 show the Week 2 trap reports for true armyworm and black cutworm, respectively.
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: