Pest & Disease Outlook for Illinois Corn

As planting progresses across the state, we’re bringing you insights from two University of Illinois specialists helping farmers stay ahead of pests and diseases that could impact the 2025 corn crop.

Dr. Nick Seiter, an entomologist with the Crop Sciences Department reminds us that predicting pest outbreaks is never straightforward, especially when it comes to corn leaf aphids and corn rootworm.

“Every year really is a completely different year,” Nick says. “These insects are migratory, and it takes the perfect storm — literally — for damaging populations to reach Illinois.”

Key insight: Corn leaf aphids migrate from the southern U.S., and their presence depends on weather conditions in states like Oklahoma and Texas early in the season — not how cold or mild our winter was.

Nick also advises farmers to scout now for early-season pests like seed corn maggots, white grubs, wireworms, grape colaspis, black cutworm, and true armyworm. These pests become more problematic when conditions are cool and wet, slowing down crop emergence and making young plants vulnerable.

Fast-growing crops can outpace insect damage, so fields that are slow to emerge need a closer look.

We also talked with plant pathologist Dr. Boris Camiletti, who’s tackling tar spot, a fungal disease that’s become a significant concern across Illinois.

“Tar spot is here to stay,” Boris says. “We’re now validating fungicides, treatment timing, and even decision-making apps that help determine if and when spraying is necessary based on local weather conditions.”

Last year, southern Illinois saw tar spot following remnants of Hurricane Hilary. But due to dry conditions afterward, the disease didn’t escalate until late in the season, past the point of yield impact. This underscores the importance of understanding disease risk and not over-spraying.

Boris is also collaborating on research into mycotoxins, which are an increasing concern for the ethanol industry. His work, in partnership with extension teams across the Midwest, aims to better understand toxin dynamics in Illinois corn.

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