Allen County Crop Scouting Update – Late July

Clint Schroeder – OSU Extension

As both corn and soybeans have entered the reproductive phase of the crop cycle it is an important time to be scouting for disease and insect issues. One of the most important parts of integrated pest management (IPM) is crop scouting. When done properly it can help farmers obtain higher yields and increased profit per acre. When heading to the field don’t forget your copy of the Corn, Soybean, Wheat, and Forages Field Guide to help determine identification and threshold levels for each disease or pest. The field guide can be purchased at the extension office if you do not already have a copy.


OSU Extension conducts weekly monitoring of Western Bean Cutworm (WBC) pheromone traps throughout the state and published the data in the weekly in the C.O.R.N. Newsletter. Those results can be found here. Trap numbers have remained low for Allen County, but there has been an uptick in surrounding counties. Now is the time to scout for egg masses on the upper leaves. Select 20 consecutive plants in 5 locations of the field. If over 5% of those plants have egg masses an insecticide application is warranted.

WBC egg mass Photo by: Amy Raudenbush, Ohio State University.

Recent weather patterns have left the region with excess moisture and humid conditions. This type of environment favors development of several types of leaf disease on susceptible hybrids. Be on the lookout for Northern Corn Leaf Blight, Grey Leaf Spot, and Tar Spot.  Consider a fungicide application if fungal disease is present on the third leaf below the ear leaf or higher on 50 percent of the plants at tasseling and the hybrid is susceptible to the disease. Moderately susceptible hybrids may require a treatment if risk factors for disease development are favorable, such as current and predicted weather conditions during grain fill, disease history of the field and previous crop. If the hybrid has good genetic resistance or tolerance to the disease, no application is needed.


The main defoliator to worry about at this stage is the Japanese Beetle. Scouting at several locations throughout a field is crucial as these pest will aggregate and be more abundant in pockets of the field. An insecticide treatment is advised when defoliation levels reach 15% in bloom, and 25% during pod fill to harvest.  These defoliation levels apply to the plant as a whole, not just certain leaves.

Brown Spot is prevalent on the lower leaves of the canopy this year, especially in fields that have saturated soils or experienced flooding. Fields in poorly drained soils may also be more susceptible to phytophthora stem canker. The best time to see symptom development is one to two weeks after heavy rains.

Example Soybean Defoliation Levels


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