Moth counts ramped up dramatically during Week 2 of the moth trapping network (April 7 to April 13), although we often get large flights with spring storm systems in April. Despite the low captures reported during the first official week, 70 total black cutworm (BCW) moths were reported last week. Most of those captures were reported on April 8 (41 moths), and 16 additional moths were reported on April 11. Two reports included significant flights: Floyd County (April 8) and Muscatine County (April 11).

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!

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.

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Photo Credit: gettyimages-songdech17