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Agronomic Crops Network

Ohio State University Extension


Foliar Diseases Already Showing up in Corn

Gray Leaf Spot on Corn

Foliar diseases, especially Gray Leaf Spot (GLS) and Northern Corn Leaf Blight (NCLB), are already showing up in some corn fields. Although this a little bit on the early side for Ohio, it is not at all surprising, since we have had several wet, humid days over the past few weeks, with moderate to warm temperatures. Both GLS and NCLB are favored by wet conditions, particularly if temperatures are within the favorable range like they have been (70 to 90 F for GLS and 66 to 80 F for NCLB).

 Northern Corn Leaf Blight

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. If it continues to rain and stays humid, this will likely not be the case in some fields this year. We are already seeing typical, well-developed lesions on the plant well before tassel (VT) in some fields.

Because of the wide variation in planting dates and weather conditions this year, the corn crop is at growth stages ranging from about V10 (ten-leaf stage) to VT across the state. With such a wide variation in crop development, if the weather continues to be favorable for disease development, some fields and some hybrids could certainly be infected early and could suffer yield reduction if not treated.

Continue to scout fields for foliar diseases, especially those planted with susceptible hybrids in an area with a history of gray leaf spot or northern corn leaf blight or in a continuous-corn, no-till field. These fields are the ones most likely to benefit from a fungicide application. 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.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.