How to use Enviro-weather’s apple scab tool

MSU’s Enviro-weather apple scab tool collects weather information to predict the progression of an apple scab infection and alerts users if protection is needed.

Spring is finally here and with it the warmth and moisture that creates ideal conditions for plant disease development. Michigan State University’s Enviro-weather website can help you manage diseases such as apple scab. Enviro-weather collects weather information, including temperatures, precipitation, relative humidity and leaf wetness, etc., at each of its 81 weather stations. Enviro-weather then uses this local weather data in research-based disease models to produce management information online.

Enviro-weather’s apple scab tool is its most frequently used crop-specific tool. It has been used more than 12,000 times per year during the last three years. This tool uses rainfall data, relative humidity, leaf wetness and temperature to predict the progression of an apple scab infection and alert users if protection is needed.

Apples are susceptible to apple scab after green tissue starts to grow (green tip). The Enviro-weather apple scab tool estimates the green tip date from temperature data.

According to the Mills Table modified by Jones, apple scab fungus needs certain environmental conditions, like leaf wetness and temperature, to begin to grow. Enviro-weather’s apple scab tool tracks times when the foliage is wet, known as “wetting periods,” and determines if the temperature is high enough and the duration of wet foliage is long enough for an apple scab infection to become established.

A wetting period starts when a rainfall of at least 0.01 inches occurs. This amount of rain is needed for the release of apple scab spores from the previous season’s fallen leaves. The wetting period is maintained, and the disease continues to develop, until leaves have been “dry” (relative humidity less than 90 percent and leaves are wet less than 15 minutes each hour) for eight consecutive hours.

The length of time it takes for the new infections to become visible depends on temperature; under cool temperatures, symptoms may not show for over 14 days. The Enviro-weather program records weather conditions and performs the complex calculations necessary to produce projections of risk and infection.

Apple scab Enviro-weather tool

How to access the apple scab tool

Go to and select the nearest weather station by clicking on the yellow dot on the map or using the pull-down menu in the upper right of the screen.

Enviro-weather homepage

Select “Fruit” from the list of commodities in the light green bar at the top of the screen.

Enviro-weather station page

Click on the folder next to “Apple” in the left column, then select “apple scab.”

Enviro-weather station page with folder open

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