Wayne County Extension IPM crop scouts are noting high incidences of grey leaf spot (GLS) in some corn fields in the area.   While northern corn leaf blight (NCLB), another corn foliar disease, has not yet been noted on our scouting reports, other areas of the state are seeing northern corn leaf blight in fields and it would not surprise me to see it in our area as well.  Both grey leaf spot and northern corn leaf blight are fungal diseases and of course what is driving the appearance of these diseases is our wet weather.  Combined with wet conditions, each disease has a preferred temperature range for its development; 70 to 90 F for GLS and 66 to 80 F for NCLB.

Foliar diseases of corn are generally a concern when they develop early and progress up the plant before grain fill is complete. This is especially true when the hybrid is susceptible. In most years, GLS and NCLB usually develops late and has very little or no effect on the crop.  Early development of the disease like we are seeing this year is more problematic because if the plant loses too much leaf area, particularly those leaves just below the ear and the leaves above the ear, then the photosynthetic ability of the plant is reduced and grain development and fill is affected.

Pierce Paul, OSU Extension Corn and Wheat Pathology specialist has the following advice for growers; continue to scout fields for foliar diseases, especially those fields where a susceptible variety was planted.  Pay particular attention to those fields with a history of gray leaf spot or northern corn leaf blight as well as continuous-corn, no-till fields.  These fields are the ones most likely to benefit from a fungicide application.  Fungicide application should be made at the VT – R1 growth stage. Use hybrid susceptibility, weather conditions, field history, and current disease level as a guide when making a decision to apply a fungicide. There are several very good fungicides to choose from. Follow the labels and keep your eyes on the fungicide price and application cost when making a decision. 

Use the information below as a guide when making your fungicide application decision:

Susceptible hybrids:  If disease symptoms are present on the third leaf below the ear or higher on 50% of the plants examined.

Intermediate hybrids:  If disease symptoms are present on the third leaf below the ear or higher on 50% of the plants examined, AND the field is in an area with a history of foliar disease problems, the previous crop was corn, and there is 35% or more surface residue, and the weather is warm and humid through July and August.

Resistant hybrids:  Fungicide applications generally are not recommended.