Michigan potato late blight update – July 24, 2019

No late blight reported. Weather-based risk remains moderate in Michigan growing regions. However, recommend intensive monitoring after confirmed reports in neighboring areas.

Michigan late blight forecast map
Figure 1. July 24, 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, potato late blight was reported in Wood County, Wisconsin, on July 17; the US-23 genotype of Phytophthora infestans was confirmed by University of Wisconsin-Madison. Also, DNA from the sporangia of P. infestans was detected in Kent County, Ontario, Canada July 15-18 from spore traps maintained by University of Guelph researchers. In Michigan, late blight risk remains moderate in most areas (Fig. 1), but intensive scouting is recommended based on these reports in neighboring areas.

Late blight is caused by P. infestans, which favors 60-80 degrees Fahrenheit 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
(Green)

Medium risk
(Yellow)

High risk
(Orange)

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

Late blight detected within 1 mile
(Red)

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 also 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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