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Corn+Soybean Digest

Defy Disease

Continuous corn could lead to continuous disease. In the past, rotation helped to control disease, but corn after corn increases the potential for disease.

“The risk of most diseases, except common and Southern rust, increases,” says Alison Robertson, Extension field crops pathologist with Iowa State University. “This is because most diseases overwinter in corn residue. For example, the anthracnose and gray leaf spot fungi survive for up to one year in corn residue.”

Diseases that could affect corn planted after corn include foliar diseases such as gray leaf spot, northern corn leaf blight and anthracnose leaf blight and eye spot, according to Pierce Paul, assistant professor and field crops research and Extension pathologist at Ohio State University.

“Economically important foliar, ear and stalk diseases are caused by pathogens that survive the winter in crop residue,” says Paul. “Planting a nonhost crop such as soybeans breaks the cycle of most corn pathogens. However, in a continuous corn cropping system, pathogens carry over from one growing season to another, eventually building up to levels likely to cause grain yield and quality losses.”

Some diseases are more prevalent in continuous corn than others.

“The spores of anthracnose are splash-dispersed and thus in continuous cornfields, the source of inoculum is right next to the host,” says Robertson. “Anthracnose leaf blight is more prevalent. The prevalence of Diplodia stalk and ear rot, northern corn leaf blight, eye spot and gray leaf spot have also been shown to increase.”

And one disease may increase the likelihood of another.

“Extensive blighting in the upper leaves due to gray leaf spot and northern corn leaf blight may lead to stalk and ear rot problems,” Paul says. “Leaves in the middle and upper parts of the plant produce most of the sugars needed for grain production, so a reduction in healthy leaf area means less sugar, leading to less grain produced. To compensate for low sugar in leaves, sugars are removed from the stalk, leading to poor stalk quality, stalk rots and lodging.”

Stalk rot fungi survive in crop residue and the soil, and stressful conditions may predispose corn plants to stalk rot.

“Stressful conditions include drought, foliar disease, hail damage, inadequate nutrition or compaction and insect damage,” says Robertson. “Most of the pathogens are specific to corn, and their populations in the residue and soil will buildup under continuous corn.”

Ear rot can also be an issue in continuous corn, as ear rot fungi also survive in crop residue and in the soil.

“It will be important to get into each field and scout for ear rot problems,” Robertson says.“If disease is a problem on more than 10% of the ears, timely harvest, quick drydown and cooling the grain temperature will be crucial to maintain quality.”

Don't get discouraged by disease, though. There are numerous ways to manage and control diseases in continuous corn, but it's going to take more time, thought, care and attention than you might be used to, says Robertson.

“Scouting for foliar diseases is critical in corn-on-corn fields to ensure that fungicide applications are applied in a timely manner, and the ear leaf and leaves above the ear are protected from infection and extensive blight development during grain fill,” she says. “Resistant hybrids, tillage and fungicide applications (for foliar diseases) are also ways to manage diseases in continuous corn.”

Hybrid selection is possibly the most important factor in managing diseases in continuous corn, according to Robertson. “Knowledge of diseases that occurred in the previous crop will enable informed decisions,” she says. “Opt for hybrids with high yield potential, good resistance to leaf and stalk diseases and good emergence and seedling vigor traits.”

Along with hybrid selection comes seed treatment fungicides and fungicide application. There are options available to purchase seed with insecticidal and fungicidal treatments. Application of fungicide is only necessary if a few lesions are observed on leaves below the ear leaf, prior to or at silking. Remember that all fungicides have a limited period of activity, experts say.

“Although planting a resistant hybrid or using a fungicide may reduce losses due to diseases in a conservation tillage continuous corn system,” says Paul, “no hybrid is equally resistant to, and no fungicide is equally effective against all the diseases likely to develop in that system.”

Managing residue could help in that aspect, though. In high-risk disease situations, such as continuous corn, strip-tillage or removing residue above the planting row might be worth considering, says Robertson.

“In situations where disease severity in the previous crop was high, strip-tillage should reduce disease risk by burying some residue and removing residue from direct contact with the crop,” she says.

Also be aware that your planting date can play a role in controlling disease.

“In cooler soils, germination, seedling emergence and seedling development are delayed, lengthening the period when germinating seedlings are vulnerable to infection by seedling pathogens and insects,” says Robertson. “Delaying planting in continuous cornfields until soil temperatures are above 55° F will reduce the risk of poor stand establishment due to seedling disease.”

The bottom line in managing disease in continuous corn is to know that more than just one management technique will have to be used.

“Growers willing to plant corn after corn will have to be prepared to use multiple management strategies to minimize disease problems,” says Paul.

Managing Disease In Continuous Corn

Here are five tips to manage disease in continuous corn from Pierce Paul, Ohio State University Extension pathologist.

  1. Use some form of tillage to bury crop residue. When not rotating crops, tillage becomes a necessity to reduce pathogen buildup from one season to the next.

  2. Plant hybrids with good disease tolerance and resistance — the more tolerant the hybrid, the less yield reduction. Also make sure the hybrid has good standability and stalk strength.

  3. Use fungicides as needed to control foliar disease when susceptible hybrids are planted and weather conditions are favorable.

  4. Base fertility programs on soil tests; avoid excessive rates of nitrogen and other nutrients.

  5. Control insect pests and weeds,as they can transmit viruses from weeds to corn. In addition, rootworm and stalk borer may cause injury to plant roots and stalks, permitting stalk rot fungi to enter the plant.

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