Cooler conditions continued into week 4, resulting in relatively few moths being caught across the state. During week 4 of the Iowa Moth Trapping Network (April 18 to April 24), our cooperators reported 56 total black cutworm (BCW) and 15 true armyworm (TAW) moths.
You may be wondering how the frigid temperatures of last week affected the moths that arrived prior to the cold snap. Well, it likely depends on the species, what life stage they had attained, and how cold it got in your area. I suspect the only life stages present in Iowa right now are adults and eggs. Not much information is available for TAW, but it appears they cannot survive below freezing (< 32°F) in any life stage. Adult BCW has little chance of survival below freezing, but eggs are the most cold-hardy stage. BCW eggs are likely to survive weeks of exposure to temperatures into the 10s (°F).
Week 4 report:
The 15 TAW moths reported last week were captured mostly in the southern half of the state (Figure 1). Black cutworm activity was statewide (Figure 2). Most of the BCW moths were reported on April 18th and 19th, just before temperatures dropped off. One significant flight occurred during week 4 in Taylor County on April 18. This is in addition to the previously reported significant flight in Taylor County during week 2 when significant flights occurred in 5 counties. You can read more about what a significant flight means in the Week 2 update.
These updates are typically a week behind. If you are interested in staying up-to-date on the moth trapping network, visit https://corn.ipmpipe.org/insects/ to see live mapping from Iowa, Wisconsin, and Illinois. The true armyworm and black cutworm pages feature 1) an interactive map showing the total count for the current 7-day window – clicking on a county will show you a line graph of trap captures; and 2) a time-lapse map of counts for the entire season. The black cutworm page also has a map that I will update with predicted cutting dates (note: this map is not real-time).
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: