A cool and rainy start to May slowed planting progress and crop emergence across large parts of the Midwest, but agronomists say the bigger challenge may be arriving now. As temperatures rise, farmers are being urged to intensify crop scouting immediately to identify early-season pest infestations, herbicide injury, and disease outbreaks before economic losses escalate.

Stephanie Porter, outreach agronomist with the Illinois Soybean Association, said plant population evaluation should be growers' top priority this week, especially in fields affected by uneven emergence, saturated soils, and delayed planting. Weed competition ranks second, as excessive moisture has created ideal conditions for aggressive early-season weed growth.

The combination of cool temperatures followed by heavy rainfall has also increased reports of herbicide stress in corn and soybean fields. Agronomists noted that symptoms appear more severe in lighter soils with low organic matter, crusting issues, or compaction problems. Saturated conditions and slow crop growth have amplified crop sensitivity to residual herbicides, adding another layer of risk for producers already facing elevated input costs.

Despite those concerns, warmer temperatures arriving across the Corn Belt could help crops recover. Many growers reported corn fields looking weak earlier this month, but recent heat may accelerate vegetative growth and stabilize yield potential if conditions improve quickly.

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Black Cutworm Flights Raise Corn Concerns

Entomologists across Illinois, Indiana, Wisconsin, and neighboring states are closely monitoring black cutworm moth flights, which have intensified throughout the spring migration period.

Kelly Estes, entomologist with the University of Illinois Extension, warned that projected cutting dates now extend through much of May, increasing the risk window for vulnerable corn fields. Wet weather, delayed planting, and heavy weed pressure are all factors that can increase infestation risk.

Agronomists emphasized that fields with cover crops, late planting dates, or dense weed growth require especially careful monitoring. While experts do not expect widespread catastrophic outbreaks, they cautioned that localized infestations could still produce significant stand losses.

Matt Montgomery, agronomic training manager at Beck's, stressed that modern seed treatments have reduced pressure from black cutworms in many operations, but scouting remains essential. He recommended weekly inspections during the first month after crop emergence to identify feeding damage before larvae become difficult to control.

Armyworm Populations Expanding Rapidly

True armyworm activity is also increasing across portions of the Midwest as moths continue migrating northward with recent weather systems.

University of Wisconsin entomologist Emily Bick warned that armyworm outbreaks can escalate extremely fast, particularly in wheat fields and grassy areas where larvae often remain hidden until damage becomes severe.

Experts recommend checking corn plants for leaf feeding and inspecting residue-covered areas where larvae may shelter during daylight hours. Agronomists advise evaluating five separate groups of 20 plants across each field, including border rows where infestations often begin.

Treatment thresholds vary depending on crop stage, but specialists warned that delayed intervention could sharply reduce insecticide effectiveness once larvae mature. In wheat, rescue treatments are generally recommended before flowering when populations exceed four larvae per square foot.

The situation is drawing concern because rapid infestations could increase production costs at a time when many growers are already balancing volatile commodity prices and tighter operating margins.

Alfalfa Weevil Feeding Accelerates

Alfalfa producers are also being warned about increasing pressure from alfalfa weevil larvae, particularly across Indiana and Michigan.

Christian Krupke of Purdue Extension said many areas have already reached thermal thresholds associated with peak larval feeding. He encouraged growers to begin scouting immediately and rotate insecticide chemistries to reduce resistance risks.

Experts also emphasized the importance of evaluating fields after treatment to confirm control effectiveness. Repeated reliance on the same pyrethroid products may weaken long-term pest management success and increase resistance development.

Michigan State University entomologist Chris DiFonzo added that farmers should not rely exclusively on degree-day models and instead prioritize direct field inspections to confirm feeding activity. In some cases, early cutting may be economically preferable to insecticide applications when harvest is close.

Fusarium Risk Climbs in Wheat Fields

Meanwhile, wheat producers face growing concerns over Fusarium head blight, also known as head scab, as warm and humid conditions develop during flowering.

Darcy Telenko, plant pathologist with Purdue Extension, warned that the disease can lead to shriveled kernels, yield reductions, and contamination from DON toxins that may lower grain quality and marketability.

Farmers are also being advised to monitor for foliar diseases including stripe rust, leaf rust, Septoria, and tan spot as environmental conditions remain favorable for fungal development.

Agronomists say this season highlights how quickly weather volatility can reshape disease pressure across U.S. agriculture. With crop insurance decisions, fungicide timing, and yield expectations all influenced by field conditions, consistent scouting may become one of the most valuable management tools of the 2026 growing season.