Updates provided by Amanda J. Gevens, Associate Professor & Extension Vegetable Plant Pathologist, Interim Co-Director of Wisconsin Seed Potato Certification Program, UW-Madison, Dept. of Plant Pathology
We have surpassed the threshold of P-Day 300 for early planted/emerged potatoes in the Grand Marsh and Hancock areas. This indicates that conditions have been met for the development of early blight, caused by Alternaria solani, in the lower canopy of potato. Early blight lesions have been slow to onset but with the warmer, wetter conditions, the disease risk is increased. Early prevention aids in limiting development of inoculum for the rest of the season, esp. when initial lesions are lower in the canopy and it can be harder to get good fungicide coverage later in the season.
We also surpassed threshold of Disease Severity Values for all potatoes in the Grand Marsh area and early and mid-planted potatoes in Hancock and Plover areas. This indicates that conditions have been met to favor the development of late blight, if the pathogen is present in the growing environment. I recommend application of preventive fungicides for late blight in these risk areas at this time.