URBANA, Ill. — Corn rootworm beetles will continue emerging throughout Illinois in early July. The University of Illinois (U of I) is currently monitoring the movement of corn rootworm in an effort to help farmers stay a step ahead of the voracious beetle. 

“We noticed the first few western corn rootworm beetles of the year at our Urbana field site earlier this week,” reported Nick Seiter, University of Illinois field crop entomologist, on June 25. “There are a number of things we can learn by keeping track of corn rootworm emergence, particularly in fields that have a history of rootworm problems.”

Since 2021, the U of I Department of Crop Sciences has participated in a regional monitoring program for corn rootworm adults. Seiter is urging corn growers to participate in the monitoring network for 2024. “We distribute traps and instructions to willing farmers and consultants every year, who set up a line of traps in a selected field(s) and report the numbers back to us. It’s an effective and relatively easy way to get a regional picture of rootworm population trends,” Seiter said. 

The rootworm emergence monitoring program helps entomologists in the following ways, according to Seiter:

Control performance: “Usually, our first indication that a local population is developing resistance to a Bt trait package is elevated numbers of beetles emerging from traited corn; if we are watching closely, we tend to notice this before larval pruning is sufficient to reduce yields. Of course, the beetles are mobile, so you should still dig some roots to see what is happening below ground, but elevated beetle numbers emerging from traited corn can be a good early indicator of resistance development,” he said.

Species complex: “While western and northern corn rootworm are managed similarly and cause identical feeding injury, there are some key differences. In particular, northern corn rootworm populations have the potential for extended diapause (a period of suspended development in insects),” according to Seiter. 

Potential for injury next season: “Observing beetle numbers during late July and early August (when egg laying usually reaches its peak) is the most reliable way to predict the potential for rootworm feeding injury to corn roots next season.”

A recent BASF Showcase Plot event in Seymour, Ill., confirmed that corn rootworm will likely present challenges for many Midwest growers this summer. Damage from tar spot in corn could rival that of 2021, when the U.S. corn crop was reduced by as many as 231.3 million bushels due to the disease, according to Mike Probst, Illinois-based technical service representative for BASF. He cautioned that areas that have previously been affected by tar spot could very likely see recurrences. 

“If you find tar spot, it’s time to take action. You can’t afford to let it go unchecked,” said Probst. 

Nick Tinsely, BASF tech service rep for seed coatings, warned that corn rootworm could emerge as a challenge to farmers as the growing season progresses. “The corn rootworm numbers we are seeing are high across Iowa through Minnesota and are moving into Illinois,” he said. 

Increased pressure from soybean cyst nematode (CST) is another concern Midwest producers are facing during the 2024 growing season, according to the Iowa State University Extension, which cautioned that soil moved by erosion due to recent heavy rains and flood waters may spread SCN to new places. 

“It is not possible to quantify the magnitude or frequency of this happening. Considering how widespread SCN already is in Iowa and the Midwest, perhaps the movement of SCN in soil moved by rainfall and flood waters will not have a great impact. Nonetheless, it is quite possible that some fields may have had SCN introduced in soil from other fields through flooding. Consequently, soil samples should be collected this fall to test for SCN in fields where soybeans will be grown in 2025,” the Iowa State University Extension and Outreach office advised farmers on June 28.

Corn growers interested in joining the U of I’s corn rootworm monitoring network for 2024 can send an email to nseiter@illinois.edu with “rootworm trapping network” in the subject line.