It was a tough planting season in part of the Corn Belt this year. Now that the crops are finally growing, you need to protect them from diseases and insects.
Which pathogens will be more prevalent this summer depends on the weather. However, cool, wet weather this spring appears ominous for the spread of northern corn leaf blight. There was a lot of this disease in residue from last year, and it likes cool, wet weather.
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Rains are good for crops, but wet weather is also good for many disease organisms that are opportunistic. It is difficult to predict which pathogens will be more prevalent this summer. However, based on the spring weather and past experience, here are some of the leaf diseases that might develop and dominate in July and August. Watch out for them.
These diseases are caused by fungi. However, there are other leaf diseases caused by bacteria.
1. Northern corn leaf blight has plenty of inoculum left from 2015.
Northern corn leaf blight can get started in residue from previous crops, which may provide the initial inoculum. It is further spread by airborne spores. NCLB likes cool, wet, humid weather. It produces long, cigar-shaped lesions that are grayish or tan.
NCLB may become a serious disease again this year. Hybrids with good tolerance are available. Ask your seeds sales rep about the tolerance of each hybrid you planted in each field. That will help you pinpoint where to scout first for this disease.
2. Southern corn leaf blight could also appear this year.
This disease makes small, elliptical lesions and can cause considerable damage in susceptible hybrids. However, it requires hotter weather than northern corn leaf blight to reach its full potential.
Foliar fungicides can be effective in controlling both northern and southern corn leaf blights if applied properly and at the right time.
3. Gray leaf spot is a big one to watch.
Gray leaf spot is a foliar disease that has established itself as one of the most important leaf diseases in the Corn Belt. It occurs on lower leaves first, but can spread to upper leaves quickly in hot and humid weather.
This disease's spots are rectangular and appear gray when mature. Hybrids with good tolerance to gray leaf spot are available. Again, check with your seed rep to see how each hybrid you planted rates on gray leaf spot tolerance. Pay special attention to hybrids that may not be as resistant to gray leaf spot as other hybrids in your lineup, particularly if weather conditions favor the disease.
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4. Anthracnose leaf blight is another disease to watch in 2016.
Anthracnose leaf blight produces small, oval to elongated lesions that become brown and spindle-shaped with yellow to reddish-brown borders. This pathogen can do well both in cool and warm, humid weather.
This disease also causes stalk rot, which can lead to considerable damage in susceptible hybrids. The leaf blight phase of this disease, which occurs in the summer, usually isn’t as serious as the stalk rot phase.
Nanda is president of Agronomic Crops Consultants LLC. Email [email protected], or call 317-910-9876.