Potato late blight has been confirmed in a commercial field in St. Joseph County, Michigan.
In a report from Dr. Amanda Gevens (University of Wisconsin-Madison), “ … late blight on potato was confirmed [July 23, 2024] in St. Joseph County, Michigan … on the southwestern edge, bordering Indiana. The genotype of the Phytophthora infestans pathogen was US-23. The disease was noted in a very small section of a commercial field (~5 sq. ft). Recall that US-23 can typically still be managed with phenylamide fungicides including mefenoxam and metalaxyl. Thank you to Rob Schafer of Mid-Michigan Agronomy for quickly working on this diagnostic and sharing the information so that producers in the region can take enhanced action to manage this disease.”
Preventative foliar programs and diligent crop monitoring is strongly recommended.
Current late blight risk is low to medium in Michigan (see attached image: the darker the green, the less the risk), however, some areas have experienced favorable conditions in the past several weeks due to more frequent and heavy rain events.
Late blight forecasting for the Upper Midwest is available through the UW-Madison Vegetable Disease & Insect Forecasting Network: https://agweather.cals.wisc.edu/vdifn?model=late-blight.
Since the early July reports of potato and tomato late blight (US-23 genotype) in Kent and Elgin counties in Ontario, Canada, no other regional detections have been documented. Current year information is available at https://usablight.org/.
No Phytophthora infestans DNA has been detected from experimental spore samplers maintained by the MSU Potato and Sugar Beet Pathology program, currently deployed in research and commercial fields in Montcalm County.
Contact MSU Potato and Sugar Beet Pathology at willbur1@msu.edu or (517) 355-4754 or MSU Plant & Pest Diagnostics at pestid@msu.edu or (517) 355-4536 to report potential late blight detections or visit our websites for more information.
– By Dr. Jaime Willbur, Assistant Professor, Department of Plant, Soil and Microbial Sciences at Michigan State University