"In the past, we've seen leaf blight show up and not cause much of a problem," says Pierce Paul, a plant pathology specialist with Ohio State University Extension. "Every single year since 2001 it has shown up at some level, which concerns me now because the levels are increasing, and it's showing up in more fields every year."
The continued and increasing incidence of the disease is indicative that farmers are still planting corn varieties susceptible to leaf blight, Paul says. He recommends farmers take stock of fields and varieties that are affected by blight this year, plant resistant varieties in those fields next year, or consider rotating affected fields to soybeans.
By continuing to plant susceptible varieties, farmers are in essence ignoring the problem, and allowing the disease to develop and spread. This increases the spore load carried over from one year to another. The fungus survives in infected corn stubble, so the more disease incidence in a given year, the more spores are carried over to the next year, increasing the chance of a bigger problem in the future.
"If we continue to plant susceptible varieties, at some point we'll build up enough stock of the disease that we're going to see a significant outbreak," he says. "The fungus is already present in our no-till or minimum-till cropping system, so once a susceptible hybrid is planted, all it takes for an outbreak to occur is a season of cool, wet weather."
In addition to planting varieties resistant to the fungus, Paul recommends using other management practices to mitigate the amount of fungus left in the field after harvest.
Farmers can "break the cycle" of the fungus by following a traditional corn-soybean crop rotation. Fields planted corn on corn are more likely to be affected by the disease. He also noted that if tillage is an option, that is another way of reducing the amount of fungus left in a field.
The biggest problem cause by northern corn leaf blight is a reduction in the surface area of the leaf available to convert sunlight into sugars necessary for grain fill."If you have reduced leaf area, the plant will not be able to produce enough sugars for grain development and grain fill," he says. "The plant will redirect sugars from the stalk into those functions, which could pose issues for stalk lodging later in the season. You might think of it as cannibalization of the plant, taking nutrients from one area of the plant to make up for a lack of photosynthetic area."