Last year was the second season of an organized, regional corn rootworm monitoring effort with the Corn Rootworm IPM working group. This working group was formed to address regional concerns as corn rootworm populations continue to overcome Bt corn hybrids and become more challenging to manage. The working group is composed of university, industry, and government personnel from 11 U.S. states and 5 provinces in Canada. You can find details about the regional corn rootworm working group on the website and in the report. The report contains information on the protocol cooperators followed, background about the network, and a summary of the results. Go to https://cornrootworm.extension.iastate.edu/adult-trapping-network and scroll down to the "Reports" heading to find a PDF of the report.
Summary of the Iowa Corn Rootworm Monitoring Network
In 2022, 145 sites were monitored and reported to the Regional Monitoring Network in Iowa; some sites were part of the Iowa State University corn rootworm monitoring network, but others were contributed by industry or independent crop consultants. Of those sites, 49 were in continuous corn production and 30 were in a corn-soybean rotation (Figure 1), and the number of years in continuous corn ranged from two to 30 years.
Overall, beetle counts were slightly higher at the monitored sites in 2022 compared to 2021, and 40% of sites in Iowa exceeded the trapping threshold of 2 beetles/trap/day in 2022 (Figure 2; compared to 35% in 2021). Only 2 sites with a corn-soybean rotation exceeded the trapping threshold in 2022.
Most sites in Iowa were dominated by western corn rootworm (111 sites), but northern corn rootworm was dominant at 19 sites (Figure 3, Table 1). The dominant species at each site was determined to be the species that represented >50% of the beetle counts during the peak week (week when the most total beetles were captured). Some sites did not have a dominant species, either because there were no beetles captured or an even number of each species was present during the peak week.
Table 1. The number of sites with each crop sequence where each species was dominant. Some sites did not have a dominant species (None).
|Dominant Species||Continuous Corn||Corn-Soybean|
|Western corn rootworm||42||13|
|Northern corn rootworm||5||8|
Many cooperators chose not to respond to the questions about field history, but 40 sites indicated a history of corn rootworm in the field. 23 sites said there was no history of corn rootworm, and 8 sites had an unknown history. Most of the sites that reported a history of corn rootworm were in continuous corn (Table 2). The most commonly reported issue was a combination of goosenecking/lodging and high beetle populations (12 sites; Table 3).
Table 2. The number of sites with each crop sequence that reported a history of corn rootworm (Yes), no history of corn rootworm (No), or were unsure of the field history (Unsure).
|History of rootworms?||Continuous Corn||Corn-Soybean|
Table 3. The number of sites with each crop sequence that reported each corn rootworm issue (or a combination of issues).
|Reported Issue(s)||Continuous Corn||Corn-Soybean|
|High beetle populations (HB)||7||1|
|Resistance to Bt (RB)||2||0|
|Resistance to rotation (RC)||1||1|
|GL + HB||11||1|
|GL + RC||0||1|
|HB + RB||2||0|
|HB + RC||0||1|
|GL + HB + RB||1||0|