Late Blight Risk Monitoring is a service provided by Michigan State University to Michigan potato growers. The objective of the program is to provide growers with up-to-date information to help them make timely and effective disease management decisions. Late blight of potato, caused by Phytophthora infestans, spreads in potato canopies by continuous leaf and stem infection when inoculum is present and favorable environmental conditions, typically moist cool weather, exist. The Late Blight Risk Monitoring website uses real-time weather data from the Michigan Agricultural Weather Network (MAWN) to estimate when conditions are most favorable for a disease epidemic and provides fungicide recommendations appropriate to that risk. For more information see: Web-interactive integration of regional weather networks for risk management of late blight in potato canopies.

The Late blight Risk Model predicts the first occurrence of potato late blight and its subsequent spread based on seasonal accumulation of severity values (DSV's; see the Explanations page for more details). Accumulation of severity values should start at plant emergence. In our model we start accumulating severity values on May 1st, but you can select your own emergence date using the "Calculate your own" emergence page. To start using the Late Blight Risk Modeling site just select the marker on the map that is closest to your location. It will pop up a dialogue with the Risk Level for your area, and you can click on it to get a spray recommendation for your area. Or as mentioned above you can use the "Calculate your own" page to get a personalized recommendation.

The markers on the map change color according to the risk level for that location. Markers can be green (low risk), yellow (medium risk), orange (high risk), purple (equivalent to pink; late blight seen within 2-5 miles) or red (late blight seen within 1 mile). For more information on how and when the colors change see the Explanations page.

The Risk Level is a estimation of whether the conditions are favorable for the initiation of a late blight epidemic and determine what the fungicide spray recommendation will be. For more information on risk levels and their corresponding spray recommendations see the Explanations page.

DSV stands for Disease Severity Value. Disease severity values are based on various combinations of the number of hours (in a given time period) with a relative humidity of 80% or greater and the average temperature during this period. They are used to predict when conditions are most favorable for disease initiation. For more information see the Explanations page.

Spray recommendations are based on data from field trials carried out at Michigan State University and other universities. For more information see Web-interactive integration of regional weather networks for risk management of late blight in potato canopies.

Recommended fungicide rates (see the Fungicide rates page) are based on field trials and the manufacturers recommended rate which can be found on the product label. For more information contact you local fungicide supplier.

P values (also known as P-day values) are used to predict early blight (caused by Alternaria solani) and the need for protective fungicides. P values are cumulative and according to the model used on this site once they reach over 300 then protective sprays must be applied. See the early blight bulletin for more information.

You can add Google Maps to your website using the Google Maps API. For more information see the Google Maps Help page.

This FAQ is updated periodically when new questions or issues arise. To contact us with questions/problems see the Contact Us page or email: