Article and update by Joan Allen for UConn Extension.
Tomato and potato growers and gardeners: Protect your crops NOW from late blight infection. The disease has been reported in Litchfield County, Connecticut on July 18, 2015. With moist weather conditions the pathogen, Phytophthora infestans, will sporulate prolifically and spread rapidly on wind currents. Fungicide products can be applied preventively to protect plants. Active ingredients to look for include chlorothalonil, maneb, mancozeb, and copper formulations. Organic growers can use copper formulations. Symptoms of late blight include large brown leaf lesions, dark brown stem lesions, and brown, bumpy and firm lesions on fruits. During humid or wet weather, white sporulation will be visible within the lesions. Infected plant parts or plants should be removed and disposed of. Bag and place in the trash or bury about a foot deep. More information and photos are available in the fact sheet at this website.