US: Pre- and early season control measures for late blight

The current issue of Potato Progress contains an excellent summary of early season late blight management issues by Phillip Wharton and Kasia Kinzer, both from the University of Idaho. According to the researchers, Phytophthora infestans, the causal agent of late blight, overwinters in potato tubers intended for planting as seed, but may also be harbored in waste or cull potatoes, or in late blight-infected volunteer potatoes left behind in the field during harvest the previous season. Volunteer potatoes have become an important perennial weed in many potato growing regions. Researchers in Washington State have reported that up to 1.1 million tubers per acre are returned to the soil after harvest. Studies with field corn showed that when volunteer potatoes were not controlled, corn yields were reduced up to 62%. Volunteer potatoes also act as hosts for a number of important pests and diseases. More