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Rain, Humidity Amplify Importance of Head Scab Management

Wheat is starting to flower in southern and central Indiana, meaning growers need to assess risk of head scab and prepare management tactics.

Head scab, also known as Fusarium head blight, is caused by the Fusarium graminearum fungus. It infects wheat during flowering, but symptoms including bleached spikelets on the head and small or shriveled grains show up later in the season.

The fungus also produces mycotoxins, which can be toxic to animals and humans when consumed in high concentrations.

“Rainy, warm and humid weather conditions favor disease development,” said Kiersten Wise, Purdue Extension plant pathologist. “We have had ample moisture this spring, but temperatures have fluctuated, and the risk of disease development is variable across the state.”

Wise said growers might want to consider a fungicide application at early flowering to suppress head scab development.

Purdue research in Indiana has shown that applications of certain fungicides are most effective at head scab management at early flowering. While there are many choices of fungicides, not all are effective. For example, Wise said fungicides with a strobilurin mode of action are not labeled for head blight suppression.

“Growers also need to be sure to follow label restrictions on how many days must pass between fungicide application and harvest,” she said.

One tool to help wheat farmers assess the head scab risk in their fields is through the free Fusariam Risk Assessment Tool provided by the Fusarium Head Blight Prediction Center, a partnership of universities and government agencies across the country. The tool can be accessed at http://www.wheatscab.psu.edu/.

The site is a model that uses weather information, including temperature, rainfall and relative humidity, to calculate risk levels for head blight.

While the tool is a good resource, Wise said growers need to remember it isn’t perfect.

“Keep in mind that the model does not provide guaranteed prediction for whether or not scab will occur in individual fields,” she said. “Additional factors, such as the local weather forecast, crop conditions and Extension commentary should be considered when assessing the level of risk.”

The U.S. Wheat and Barley Scab Initiative also has a system in which wheat growers can sign up for alerts that update them on the risk of scab. Sign up at http://scabusa.org/fhb_alert.php.

Source: Purdue University Extension

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