Over the last week, we have seen more moth activity across the state (April 20 – April 26). Windier conditions and some of the storm systems that moved through the state this last week likely helped move moths into Iowa. Both black cutworm and true armyworm species take advantage of powerful low-level jet streams at night to move long distances from their overwintering sites in the south.
Black Cutworm Moth Activity Update
A total of 77 black cutworm (BCW) moths were reported last week. Four reports included significant flights: Hamilton County (April 20), Polk County (April 25), Story County (April 21). and Washington County (April 20).
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. We will predict cutting dates across the state by the middle part of May, and they will be shared on ICM News, so make sure you are subscribed!
Figure 1 below shows where moth traps are established throughout Iowa and summarizes black cutworm moth trap captures by county.
True Armyworm Moth Activity Update
For true armyworms, 54 total moths were reported over the last week. Figure 2 below shows where the traps are established, and true armyworm moth trap captures by county.
Additional information
Follow this link to see the first moth trapping update for 2025. 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/. (*Please note that we are still working on getting the Iowa data included on this map for 2025.)
Surrounding states also monitor and report black cutworm and true armyworm 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:
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on April 27, 2025. The information contained within may not be the most current and accurate depending on when it is accessed.
- Field Agronomist in EC/SE Iowa