Michigan potato late blight reported on August 5, 2024

Jaime Willbur<willbur1@msu.edu>, Michigan State University, Department of Plant, Soil and Microbial Sciences -

Late blight confirmed in an additional field in St. Joseph County, Michigan.

3 different pictures showing the dark brown lesions on potato leaves.
Figure 1. Examples of potato late blight on whole plant (top) with typical water-soaked lesions on forward (bottom left) and reverse (bottom right) sides of leaves. Light green border sometimes present around lesions. Faint gray-white, fuzzy growth observed at margins of lesions on the underside of leaves, apparent in humid conditions. Photo by Jaime Willbur, MSU.

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 the 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, 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 University of Wisconsin-Madison Vegetable Disease & Insect Forecasting Network. 

Map of Michigan showing areas at risk of potato late blight.
Figure 2. Aug. 5, 2024, late blight risk as reported by the UW-Madison Vegetable Disease & Insect Forecasting Network: https://agweather.cals.wisc.edu/vdifn?model=late-blight. Green = very low, light green = low, yellow = medium, orange = high, and red = very high.

Following the July 3 and 5 reports from Elgin and Kent counties in Ontario, Eugenia Banks, PhD, reported an additional detection in the Alliston area of Simcoe County, Ontario, from July 10.

On July 29, a report was released of molecular detection of P. infestans sporangia in Grand Falls, New Brunswick, from Kutay Ozturk, PhD (ibrahim.ozturk@maine.edu). "One single late blight spore was reported in one of the spore traps in Grand Falls, New Brunswick. 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 five-day spray schedule with good coverage."

No Phytophthora infestans DNA has been detected from experimental spore samplers maintained by the Michigan State University (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.

Please contact the 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. 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 at 269-858-8739 or ritchi67@msu.edu.

 

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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