Corn Earworm Adult Flights Increase In Minnesota

Authors: Dr. Yucheng Wang, University of Minnesota, Postdoc Researcher, Dr. Fei Yang, University of Minnesota, Extension corn entomologist

Corn earworm (CEW), Helicoverpa zea, adult activity has increased sharply across several areas of Minnesota since last week (The week of August 10th, 2026), indicating that a major moth flight is underway in parts of the state. CEW adults are primarily nocturnal, with flight activity beginning around dusk. Females preferentially lay most of their eggs directly on fresh, green corn silks. After hatching, larvae initially feed on silks before moving down the silk channel to the tip of the ear, where they feed on developing kernels (Figure 1). CEW generally cannot overwinter in the Upper Midwest, with its northern overwintering limit generally estimated near the 40th parallel. Most CEW moths found in Minnesota migrate from southern states during the growing season. Minnesota typically experiences two major periods of CEW migration. An earlier, generally smaller flight may occur around mid-June, while a more significant series of flights often begins in late July or early August. The duration and size of these late-season flights will vary considerably, depending on the wind patterns coming from the Gulf Coast region, and the size of southern source populations in a given year. 

CEW larva feeding on sweet corn kernels (Photo: Fei Yang, University of Minnesota)

Since late June, we have deployed Hartstack pheromone traps at five locations across Minnesota to monitor CEW adult activity. Last week, particularly high moth captures were recorded at two sites. One trap in Nicollet County captured 462 CEW moths for weekly monitoring (Figure 2), and another trap in Redwood County captured 366 moths. At our Benton and two Dakota County locations, trap catches ranged from approximately 12 to 56 moths per trap. 

CEW moths captured in Nicollet County, Minnesota. (Photo: Yucheng Wang, University of Minnesota)

For sweet corn in Minnesota, pheromone trap captures, together with the presence of fresh green silks, can be used to guide insecticide applications. When fewer than five CEW moths are captured per night, insecticide treatment is generally not needed. 

• When catches exceed five moths per night, vulnerable silking sweet corn should be protected, with insecticide applications typically made at 4-6 days intervals. 
• Under very high moth pressure, such as more than 50 moths per night, intensive management may be necessary, with spray intervals shortened to approximately 2-3 days. 

With the recent increase in moth captures, silking sweet corn may face greater egg-laying pressure in affected areas of Minnesota. Growers should continue to monitor local CEW activity and the growth stage of their corn closely, particularly the presence of fresh green silks. In general, early planted sweet corn in Minnesota is less likely to experience severe CEW injury because it often completes silking before moth populations reach their seasonal peak. In contrast, late planted sweet corn that silks from late July through August can be at considerably greater risk of infestation across the state. Because CEW populations and moth flights can vary substantially among locations and over time, local pheromone-trap monitoring remains important for making timely management decisions.