Michigan potato late blight forecast - August 7, 2018

No late blight reported, however, recent weather was favorable for disease. Risk is moderate for all Michigan potato growing regions.

No potato late blight has been reported this season in Michigan, however, recent cooler, rainy weather is favorable for disease development. Late blight risk is at moderate levels in all areas (Figure. 1). We strongly recommend intensive monitoring of potato crops for late blight detection. Samples should be submitted to MSU Plant and Pest Diagnostic Services and reported to MSU Potato Disease, your local Michigan State University Extension expert, also availible at 888-MSUE4MI (888-678-3464).

Late blight is caused by Phytophthora infestans, which favors 60 to 80 degrees Fahrenheit temperatures, high humidity and frequent rainfall. This online forecasting tool calculates disease severity values (DSVs) based on the duration of temperature and relative humidity conditions that are favorable for disease development. Accumulated DSVs (based on early May emergence) are used to determine the local late blight risk level, indicated by the color of the map marker pins:

Low risk


Medium risk


High risk


Late blight detected within 2-5 miles


Late blight detected within 1 mile


The Michigan late blight forecast tool is currently calculating 2018 risk predictions. This tool was developed by Baker et al. 2002 and weather data used in this model is provided by MSU’s Enviroweather. A customizable tool for early to late emergence scenarios is currently in development. Answers to frequently asked questions about this forecast tool are available here


Figure 1. August 7, 2018 – Michigan late blight forecast based on accumulation of disease severity values (DSVs) since early May emergence. Yellow pins indicate medium risk areas. Photo by Jaime Willbur, MSU Extension. 

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