The trapping season for true armyworm (TAW) and black cutworm (BCW) has come to an end. We appreciate our cooperators for tirelessly checking traps over the last two months and reporting their captures so we can provide the most accurate scouting information for these pests. To recap, we had 44 volunteers participate from 32 counties in Iowa. A total of 46 BCW and 45 TAW traps were placed and monitored during April and May. Because of these efforts, we were able to provide weekly updates on moth activity and predict cutting dates for BCW in Iowa.
Week 9 report:
Last week, our cooperators reported 17 TAW (Figure 1) and 67 BCW (Figure 2) moths statewide. Most of these reports occurred between May 25 and May 27. No additional significant flights of black cutworm occurred during Week 9.
Final numbers:
Although more total moths in an area does not necessarily mean you can expect more damage to occur, knowing where moths were captured can give an idea of where to expect activity. Scouting is the only way to confirm whether larvae are present and whether management is needed. Figures 3 and 4 show the total number of true armyworm and black cutworm moths reported, respectively, in each county from April 1 to June 1. In total, our cooperators reported 389 TAW and 704 BCW moths across the state during the trapping season.
Remember to scout!
You may recall that we predicted cutting dates for BCW in early May and that updated cutting dates were included in weekly updates and on https://corn.ipmpipe.org/insects/black-cutworm/. Although no new significant flights occurred last week, continue to scout cornfields weekly until V5 to account for any prolonged arrival of BCW larvae into the area.
No such thresholds exist for TAW, so captures reported here should be used as a guide to begin scouting for TAW larvae in corn. Larvae defoliate leaves throughout the summer, sometimes leaving only stalks and midribs behind. Crops are typically damaged by larvae that move from field borders, grassy weeds in the field, or cover crops. The University of Minnesota has a good resource for armyworm identification, scouting, and management.
Report larvae!
If you see larvae or evidence of feeding by either pest, please email bugtraps@iastate.edu and include species, larval size, and date observed. This can help us refine our predictions in the future.
Past reports and other information:
Follow the links to see reports from Week 1, Week 2, Week 3, Week 4, Week 5, Week 6, Week 7, and Week 8. See our initial estimation of cutting dates across Iowa here. 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/.
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:
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 June 1, 2022. The information contained within may not be the most current and accurate depending on when it is accessed.
- Extension Education Specialist, Entomology