The tar spot fungus, officially known as Phyllachora maydis, was identified on corn leaf samples collected in commercial fields by Monsanto breeders and pathologists. The diseased samples came from DeKalb, LaSalle and Bureau counties.
The pathogen is new to the area, University of Illinois Plant Clinic director Suzanne Bissonnette said.
“This disease is typically found in the highlands in southern Mexico or in the mountains of Central America,” she said. “It likes cooler temperatures with a lot of humidity.”
Spores most likely blew in, as many others do each year, Bissonnette said. This time, the weather conditions were right for it to develop into the tar spot.
“This year, the temperatures in northern Illinois were receptive to the disease,” she said. “We had a cooler and very wet summer and fungal diseases are dependent on environmental conditions.”
The circular and oval fungal spots are tiny, but can merge and create diseased areas up to three-quarters of an inch. The tar spotting isn’t likely to affect the crop yield because it’s so late in the season, Bissonnette said. It’s unclear whether the disease will survive through the winter and live on to impact future crops.
“This is the kind of fungus that requires living tissue to be active,” Bissonnette said. “Our winters aren’t exactly the same as winters on a mountain in Central America. I would suspect if it’s anything like similar pathogens, it would have the ability to blow in each year.”
(Source – http://www.daily-chronicle.com/2015/09/22/fungal-disease-infects-some-of-dekalb-county-corn-crops/apgc8sl/)