Protect your investment, look for corn disease
July 15, 2920
This corn leaf shows classic symptoms of tar spot, a disease that first appeared in the Midwest only a couple of years ago.
Rains are good for crops, but wet weather is also good for many diseases. Leaf diseases, which may develop and dominate in July and August, are usually caused by fungi, although some are caused by bacteria. Leaf diseases to watch for this year include:
Northern corn leaf blight: This disease, which likes cool, wet and humid weather, can get started from the residue of previous crops, which provides the initial inoculum. It is further spread by airborne spores and produces long, cigar-shaped lesions that are grayish or tan in color. NCLB and gray leaf spot are two of the more common corn leaf diseases in the eastern Corn Belt.
Southern corn leaf blight: This disease, which requires hotter weather than NCLB, can cause considerable damage in susceptible hybrids. However, with hybrids commonly used today, it’s typically not a major issue in the eastern Corn Belt. To spot it, look for smaller elliptical lesions.
Gray leaf spot: Caused by a fungus, this disease has established itself as one of the most important leaf diseases in the Corn Belt. It occurs on lower leaves at first but can spread to upper leaves quickly in hot and humid weather. The spots are rectangular and appear gray when mature. Like all leaf diseases, gray leaf spot becomes more critical when it invades the ear leaf and then moves above the ear leaf.
Anthracnose leaf blight and stalk rot: This pathogen can do well both in cool and warm, humid weather. This disease also causes stalk rot, which can cause considerable damage in susceptible hybrids. The leaf blight phase isn’t as serious as the stalk rot phase. Look for small, oval-to-elongated lesions that become brown and spindle-shaped with borders that are yellow to reddish-brown.
Northern leaf spot: This disease is favored by moderate temperatures and high relative humidity. Crop residue, husks and stalks of the previous crop can provide the initial infection. It’s likely to be more of a problem in seed fields.
Common rust: A fungal disease that likes cooler temperatures, common rust appears as small spots on leaves that look like rust. In severe cases, thousands of these spots combine and kill leaves.
Southern rust: This disease likes hot and humid weather. Spores are usually blown into the Corn Belt from the south. While southern rust depends on storms to bring it north, it can appear at any time during the season. It can also spread fast unless checked by foliar fungicides.
Tar spot: This relatively new corn leaf disease is worse in northern counties but is moving south. It is caused by two fungi that affect husk leaves and has caused substantial yield losses in tropical areas, and now in some Corn Belt fields. It produces small black spots that look like spots produced on cars from driving on a newly paved road, hence its name.
Seed Genetics Direct offers hybrids with good tolerance for most of these diseases, as well as foliar fungicides that, when applied at the right time, have quite effective control.