Tar spot, a fungal disease of corn, was confirmed in north central Indiana, the first known instance of the disease in the U.S., said Purdue U. The specific disease found in Indiana has minimal effect on yields in regions, including Central America and Mexico, where tar spot is common. Other fungi that cause tar spot can cause large losses in yields, says a USDA fact sheet citing losses of up to 75 percent in Guatemala. The average yield loss in Mexico is 8 percent but there have been instances of 30-percent loss.
With the U.S. corn harvest in its early stages and the crop late in the growing season, growers do not need to take steps to control the fungus, according to experts.
Plant pathologists Kiersten Wise and Gail Ruhl said they and Purdue colleagues are trying to determine how tar spot arrived in Indiana and how to prevent further outbreaks. Purdue diagnosed the disease in its lab and the USDA confirmed the finding. Tar spot initially appears as brownish lesions on corn leaves. Black structures, which produce spores, appear later and make the leaves rough to the touch.