Late Blight Update August 9, 2018
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
Late blight has been confirmed today in commercial potatoes in southern Adams County, as well as northern Marquette County. We are working to genotype the pathogen at this time. The lesions were hard to spot, as per crop scouts, but were classic with brown, water soaked discoloration on stems and leaves with sporulation on leaf undersides.
Additionally, late blight was confirmed in Illinois on potato yesterday. The genotype on that sample is US-23 (can still generally be controlled with mefenoxam/metalaxyl).
More info to come as we complete our tests.
Be on the look out for symptoms in hard to treat areas (tree lines, under irrigation pivots), especially if fields are treated aerially. And, Phytophthora nicotianae has also been around this season. As such, don’t assume late blight, but check for sporulation and feel free to connect with myself or Brian Hudelson in the UW Plant Disease Diagnostic Clinic for confirmation.
Fungicide information is provided at link below.