Guard Against Northern Corn Leaf Blight

Northern corn leaf blight, caused by the fungus Exserohilum turcium, typically occurs in wet and humid conditions. It can rob yields if it occurs during corn tasseling and silking development. In dry weather, the disease rarely occurs or does not spread enough to cause significant economic damage. The same is true for southern corn leaf blight, although it is caused by a different fungus, Bipolaris maydis.

Farmers need to be aware of the factors influencing northern corn leaf blight, such as environmental conditions in a particular growing season, cropping practices and corn hybrids.

Identification and Lifecycle

Northern corn leaf blight appears as oblong lesions shaped like a cigar that are grayish-green or tan in color. Ranging in length from 1 to 7 inches, the lesions develop on the lower corn leaves and spread to other corn foliage, including husks, as the disease progresses. When leaves are covered with multiple lesions, the appearance is similar to that of the effect of a killing frost—brittle and a gray-green in color.

While disease symptoms typically are seen late in the growing season, cool and wet summers allow the disease to develop earlier.

Northern Corn Leaf Blight
Northern corn leaf blight is easily identified by the 1- to 7-inch cigar-shaped lesions on lower leaves, which may be grayish-green to tan in color. Photo courtesy of AgStock Images.

The northern corn leaf blight fungus overwinters on crop residue remaining on the soil, particularly in continuous corn grown under no-till and reduced tillage cropping systems. With warmer spring and summer temperatures, fungus spores reproduce on crop residue and are spread by wind or the action of rain splashing onto the new corn crop. In addition to corn, hosts for northern corn leaf blight include sorghum, millet, Johnsongrass and some additional grass species.

To develop, the fungus requires temperatures of 64 to 81 degrees F with six to 18 hours of water on leaf surfaces during wet, humid weather, according to Purdue University Extension. Typically, conditions such as cloudy days and heavy dew in fields along fence rows, tree lines and in bottomland, where humidity and dew last longer, are most favorable for the development of northern corn leaf blight. After seven to 12 days following these ideal environmental situations, lesions can begin to develop.

Crop Damage

Yield-robbing infections of northern corn leaf blight occur when susceptible hybrids are grown in high-residue fields where no-till and reduced-tillage practices are used. The leaves of infected corn plants can be completely destroyed by multiple lesions, resulting in a lack of carbohydrates needed for grain fill and maximum corn yield. With the added stress of northern corn leaf blight, infected corn plants are also more susceptible to stalk rot.

Yield losses as high as 50 percent may result if northern corn leaf blight becomes well established before silking, according to The Ohio State University.

Managing Northern Corn Leaf Blight

Farmers have a range of options to manage northern corn leaf blight, including hybrid selection, scouting, cultural practices and fungicides. A combination of these crop protection practices provides optimum security to enhance corn yields and should be implemented to sustainably manage corn diseases.

Hybrid selection

Planting corn hybrids with disease resistance is the most economical and effective way to avoid diseases such as northern corn leaf blight. Michigan State University recommends that farmers choose hybrids with good resistance scores. While no hybrids are resistant to all diseases, even partial resistance offers significant disease control to help protect yields. Disease-resistant hybrids are especially important to protect against leaf blights such as northern corn leaf blight, which can devastate a corn crop during or before the first four weeks after pollination, according to Cornell University.


Scout for symptoms of corn leaf blight when ideal environmental conditions favor disease development, especially during or before pollination. Check corn leaves for signs of blight every four weeks from the whorl through dent stage. Sampling, pest identification guides, the local Extension office, local agronomists and good note-taking for the development of field history maps are excellent sources to aid decision-making for appropriate control measures. A helpful summary of the top 10 scouting tips is available from Farm Journal agronomists.

Cultural practices

Crop rotation remains a solid tactic to help diminish disease threats. Rotating from corn to non-host crops helps reduce favorable environmental conditions for disease pathogens, risk of infection and disease levels. Any type of tillage that helps reduce crop residue from a previous corn crop will help manage northern corn leaf blight and other diseases overwintering in corn residue. Using a combination of management practices is particularly recommended in continuous corn grown with no-till and reduced tillage cropping systems, according to University of Illinois Extension.


Foliar fungicides may be applied early in the growing season to corn seedlings as a risk-management tool for northern corn leaf blight and other corn diseases, including anthracnose leaf blight and corn eyespot. After northern corn leaf blight is identified during the growing season, fungicides should be applied early in the disease outbreak for maximum effectiveness.

Delaro® fungicide offers preventative and curative defense against yield-robbing diseases, including gray leaf spot, northern corn leaf blight, anthracnose leaf blight and southern rust. This versatile fungicide has application flexibility — at-tassel timing (VT to R2), in combination with a herbicide (V4 to V7) and/or in between (V8 to VT). Delaro can be applied by air, ground or by chemigation and can be mixed with adjuvants, herbicides, insecticides and micronutrients.

Before applying any fungicide, please read the entire label for the best possible results and to confirm that the product is effective on the disease you need to control. Not every product is suitable for every situation, and correct application technique will ensure the best results.

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