Michigan potato late blight update - Aug. 14, 2019

No late blight reported. Weather-based risk remains moderate in Michigan growing regions. Continued confirmed reports in neighboring areas.

Michigan late blight forecast
Figure 1. August 14, 2019 – Michigan late blight forecast based on accumulation of disease severity values (DSVs) since early May emergence. Yellow pins indicate medium risk areas and green pins indicate low risk.

No potato late blight has been reported yet this season in Michigan. However, late blight has been confirmed in five counties in Wisconsin (A. Gevens, University of Wisconsin-Madison). Confirmed reports were on potato (Wood, Portage, and Waushara counties) and tomato (Monroe and La Crosse counties); the US-23 genotype of Phytophthora infestans was confirmed in Wood, La Crosse, Portage, and Monroe counties by UW-Madison. In Michigan, late blight risk remains moderate in most areas (Fig. 1), but intensive scouting is recommended based on these reports.

Late blight is caused by P. infestans, which favors 60-80°F temperatures, high humidity, and frequent rainfall. The Michigan late blight forecast tool is currently calculating 2019 risk predictions. 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

This tool was developed by Baker et al. 2002 and weather data used in this model is provided by the Enviroweather. A customizable tool for early or late emergence scenarios is now available.

Please visit the MSU Potato and Sugar Beet Pathology website for more information. Answers to frequently asked questions about this forecast tool are also available.

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