Michigan potato late blight forecast – Aug. 30, 2018

No additional late blight detections reported. Recent weather has increased risk to high levels in some northern Michigan growing regions.

Michigan late blight forecast
Figure 1. Aug. 30, 2018 – Michigan late blight forecast based on accumulation of disease severity values (DSVs) since early May emergence. Orange/red pins indicate high risk areas, purple pins indicate late blight detected within 2-5 miles.

Other than the late blight confirmed in Monroe County, no additional potato late blight has been reported. Recent cooler, rainy weather, however, is favorable for disease development and late blight risk has increased to high levels in some areas of northern Michigan (Fig. 1). Intensive monitoring of potato crops for late blight detection is strongly recommended. Samples should be submitted to Michigan State University Diagnostic Services and reported to MSU Potato Disease or your local MSU Extension expert (find an expert or call 888-678-3464).

Late blight is caused by Phytophthora infestans, which favors 60-80 degree Fahrenheit temperatures, high humidity and frequent rainfall. The Michigan Late Blight Forecast 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
(Green)

Medium risk
(Yellow)

High risk
(Red/Orange)

Late blight detected within 2-5 miles
(Purple/Pink)

Late blight detected within 1 mile
(Red)

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 Michigan State University 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.


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