State pathologist Mohammad Babadoost reports downy mildew of basil was detected in Illinois on July 19th for the first time this season. This disease can spread quickly statewide in wet conditions so growers are advised to begin scouting now. Three registered fungicides; Quadris, Revus, and Ranman are very effective for control of downy mildew of basil and should be spray-applied at 7-day intervals at the first sign of the disease in the field. For more information:
http://web.extension.illinois.edu/mms/downloads/71032.pdf