Potato late blight has been confirmed in an additional commercial field in St. Joseph County, Michigan. Late blight on potato was confirmed over the weekend and reported Aug. 5, 2024 in St. Joseph County, Michigan.
The genotype of the Phytophthora infestans pathogen was US-23. The disease was noted on several plants scattered on the northern edge of a commercial field. Sanitation and management measures are being applied and vine-kill of the entire field will commence as soon as weather conditions permit.
Recall that US-23 can typically still be managed with phenylamide fungicides including mefenoxam and metalaxyl. Acknowledgement to Rob Schafer of Mid-Michigan Agronomy for timely report of this detection and genotype so that producers can take action and precaution to manage this disease. Preventative foliar programs and diligent crop monitoring is strongly recommended.
Current late blight risk is generally medium in Michigan. (See attached map; green indicates little risk, yellow indicates medium 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.
Following the July 3 and 5 reports from Elgin and Kent Counties in Ontario, Dr. Eugenia Banks reported an additional detection in Alliston area of Simcoe County, Ontario from July 10.
Other information, on July 29 a report was released of molecular detection of P. infestans sporangia in Grand Falls, New Brunswick from Dr. Kutay Ozturk (ibrahim.ozturk@maine.edu). "One single late blight spore was reported in one of the spore traps in Grand Falls, NB. Currently, no late blight was detected in foliage. Current weather conditions in most potato-growing regions in Maine are conducive to disease formation if a spore falls on unprotected foliage. It is recommended to stay vigilant in scouting efforts, especially in fields close to Grand Falls, and continue the 5-day spray schedule with good coverage."
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. More information from samples exposed this past week will be available in the next day or two.
For more information, contact 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. Nicolle Ritchie is the Michigan State University Extension Field Crops Agronomist Educator working in Southwest Michigan and may also be contacted with questions or further information (269-858-8739; ritchi67@msu.edu).