If Southern Corn Leaf Blight Strikes

Southern corn leaf blight, caused by the Bipolaris maydis fungus, is most likely to occur in areas with a damp, humid climate where temperatures range from 68 to 89 degrees F. The disease does not develop or slows during sunny, dry weather. Similar to many other row-crop diseases, it’s prone to infect fields with high crop residue conditions common under no-till and reduced-tillage farming practices. The same is true for the northern corn leaf blight, although it’s caused by a different fungus, Exserohilum turcium.

Identification and Lifecycle

Southern corn blight causes corn-leaf lesions ranging from ¼ to ¾ inches in length. The elongated (egg-shaped) lesions appear tan-colored between leaf veins. Depending on the hybrid that is infected, lesions may differ in development. Lesion symptoms are usually seen on lower leaves and continue to move up the corn plant.

Southern corn leaf blight overwinters in residue from the previous year’s corn crop. Spores, which are produced on corn residue as spring weather warms, are wind-dispersed or rain-splashed onto new corn plants where they germinate. Typically, the earlier disease infection occurs, the more potential it has to reduce corn yields.

When southern corn blight develops rapidly under ideal environmental conditions—warmth and moisture—its lifecycle lasts only 60 to 72 hours. Typically, southern corn blight occurs from mid-whorl development up to corn maturity.

Symptoms of southern corn leaf blight progress into long, oblong, tan or grayish lesions. Photo courtesy of: USDA-ARS/Keith Weller.

Crop Damage

Southern corn leaf blight earned its place in history during an epidemic in 1970. During that summer, the southern leaf blight epidemic reduced corn yields by 20 to 25 percent nationwide, resulting in an estimated $1 billion loss. This epidemic underscored the need for genetic diversity, led to the development of certified seed and is the reason why detasseling of hybrid seed corn fields still exists today as a common cultural practice. Genetic diversity remains one of the most effective methods to manage southern corn leaf blight.

When southern corn leaf blight lesions occur, they can merge to kill large areas of corn leaf tissue. The result is reduced photosynthesis, which can increase stalk rots and reduce yield potential.

Managing Southern Corn Leaf Blight

Farmers can benefit from several options to manage southern 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

Choosing corn hybrids with genetic disease resistance offers the best economical and effective defense against southern corn leaf blight and other diseases. Although no hybrid provide resistance to all diseases, even partial resistance goes a long way in protecting corn yields.

Scouting

Early and frequent scouting for diseases is a routine best management practice to manage pest problems before they lead to economic damage. In the case of southern corn leaf blight, generally observe for symptoms in the lower plant leaves, which become nutrient stressed with the disease. Symptoms are typically not found at the ear leaf or above. The best time to scout is at tasseling through the R4 growth stages, earlier in seed production fields. AgWeb offers a helpful summary of scouting tips.

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 reduces crop residue from a previous corn crop will help manage southern corn leaf blight and other diseases overwintering in corn residue. A combination of integrated management practices is especially recommended in continuous corn grown with no-till and reduced-tillage cropping systems, according to University of Illinois Extension.

Fungicides

Foliar fungicides may be applied early in the growing season to corn seedlings as a risk-management tool for southern corn leaf blight and other corn diseases, including anthracnose leaf blight and corn eyespot. After southern corn 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.