Michigan potato late blight forecast – July 25, 2018

No late blight reported. Risk is moderate for all Michigan potato growing regions.

Late blight forecast map
Figure 1. July 25, 2018 – Michigan late blight forecast based on accumulation of disease severity values (DSVs) since early May emergence. Yellow pins indicate medium risk areas.

The Michigan Late Blight Forecast Tool is currently calculating 2018 risk predictions. No potato late blight has been reported this season in Michigan. Late blight risk remains at moderate levels in all areas (Fig. 1).

Late blight is caused by Phytophthora infestans, which favors 60-80 degree 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

This tool was developed by Baker et al. 2002 and weather data used in this model is provided by the Michigan State University Enviroweather. A customizable tool for early to late emergence scenarios is currently in development.

Please visit the MSU Potato Disease website for more information. Answers to frequently asked questions about this forecast tool are available.

Other diseases

Recent wet, cooler weather may promote the development of other diseases. White moldpotato early die and early blight have been observed under heavy irrigation in research fields with a history of high disease pressure. Continue monitoring fields.

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