Risk of Wheat Scab Elevated to Moderate to High - UNL CropWatch, May 26, 2011

Risk of Wheat Scab Elevated to Moderate to High - UNL CropWatch, May 26, 2011

May 26, 2011

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With the recent rainfall and wheat flowering occurring or approaching, the National Fusarium Head Blight Risk Assessment Tool has elevated the risk of scab from low to high in an area of southeast Nebraska and to moderate in areas of eastern, south central, southwest, and north central Nebraska  (Figure 1). This follows a significant amount of rainfall during the second half of last week and the first half of this week. The two high risk areas were designated today.

Map of Wheat Scab Potential

Figure 1. On May 26, the National Fusarium Head Blight Risk Assessment tool increased an area of southeast Nebraska from moderate to high risk for fusarium head blight.  See daily risk updates on the national site.

Scab appears in the field as prematurely whitened or bleached heads. Affected heads are partially or entirely bleached and often are seen suddenly scattered over small, large, or entire areas of the field.

It is recommended that a fungicide be applied at early flowering to suppress scab in scab-prone areas (southeast, south central, and southwest Nebraska). The fungicides Prosaro and Caramba are good in suppressing scab and very good to excellent in controlling foliar diseases.

Timing of Fungicide Critical

Timing of fungicide application for scab suppression is critical. Early flowering is the optimal time. Once bleached heads appear scattered in the field, it is too late to apply a fungicide for scab suppression.

For fields where wheat is not flowering yet, if foliar disease pressure is low and the flag and flag -1 leaves are free of disease, delay a fungicide application until early flowering and then apply a fungicide that will both suppress scab and provide protection against foliar diseases.

If foliar disease pressure is high and the flag leaf is at risk of infection, consider applying a fungicide to protect the flag leaf and monitor the risk of scab as heading and flowering approach. In this case a second fungicide application to suppress scab may be warranted in high risk and high yield potential fields, such as irrigated fields, if the risk of scab rises prior to flowering.

Refer to the fungicide table for a list of fungicides and their efficacy against various diseases.

Stephen Wegulo
Extension Plant Pathologist


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