Market News & Headlines >> Corn Tar Spot Confirmed in Indiana
Purdue Extension plant pathologists have confirmed the presence of tar spot, a corn fungal disease not previously reported in the U.S., in plant samples collected from a field in the Cass/Carroll county area of north central Indiana.
The specific type of tar spot found in the state has had minimal impact on yield in other areas where it is endemic, including Mexico and Central America, and experts say no action is needed to manage it this late in the growing season.
"We are still determining the impact, if any, that the disease may have in Indiana," said Kiersten Wise and Gail Ruhl in an article published in the latest issue of Purdue's Pest and Crop online newsletter. "However, it is important to alert Extension specialists if you observe the disease to accurately document its distribution in the state."
Initial symptoms of tar spot are oval to irregular bleached to brown lesions on leaves corn leaves. Black, spore-producing structures called ascomata appear later, protruding from the leaf surface and giving the leaf a rough or bumpy feel.
"The structures can densely cover the leaf and may resemble mature, black pustules present on leaves due to infection by rust fungi," the authors say. "Lesions with these ascomata may coalesce to cause large areas of blighted leaf tissue, which can be mistaken for saprophytic growth on dead leaf tissue." Symptoms and signs of tar spot might also appear on leaf sheaths and husks.
The authors say tar spot can be caused by two different fungi - Phyllachora maydis and Monographella maydis. So far, only Phllachora maydis, which is not considered a significant yield threat, has been found in Indiana. Infections by Monographella maydis, on the other hand, can cause economic damage.
The fungi have not previously been reported to be seed-borne, so no phytosanitary restrictions accompany the tar spot confirmation. The disease was diagnosed at the Purdue Plant and Pest Diagnostic Laboratory and confirmed last week by a USDA national fungal identifier located in Beltsville, Maryland.