Purdue researchers adopt interdisciplinary approach to assessing emerging tar spot disease in corn For more than a century, tar spot fungal disease in corn kept its distance from the U.S., biding its time. “Tar spot had not been detected in the U.S. prior to 2015, but it has been endemic in several Latin American countries, starting in Mexico in 1904,” said C.D. Cruz, associate professor of botany and plant pathology at Purdue University. Tar spot afflicted two of Indiana’s 92 counties in 2015. By 2022, only a few had managed to remain unscathed. At that time, the fungus had extended to 16 states and Ontario, Canada, according to the Pest Information Platform for Extension and Education.