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. This follows a significant amount of rainfall during the second half of last week and the first half of this week.
Meanwhile, wheat in south-central, central and western Ohio was reaching the critical flowering growth stage. With more rain in the forecast, it was expected that an increase in the risk for scab was present, since the scab fungus thrives under wet, humid conditions.
"The risk tool is now showing moderate to high risk for scab in some of the areas where the crop is flowering or will reach this growth stage over the Memorial Day weekend," says Ohio State University plant pathologist Pierce Paul. "Producers in these areas should consider a fungicide application at flowering (Feekes 10.5.1) to suppress scab and vomitoxin."
Prosaro, Caramba and Folicur (or other tebuconazole) are recommended for scab suppression, says Paul, adding that Prosaro and Caramba perform better against scab and vomitoxin than Folicur and other tebuconazoles.
Paul says questions have been asked about fungicide application after flowering for scab control. Applications made 2 to 4 days after flowering will still provide some level of suppression, but efficacy drops considerably as you more away from flowering. In addition to being less effective, with late application you run the risk of getting into the pre-harvest interval, which is 30 days for Prosaro, Caramba and Folicur, Paul reports.
The forecast called for drier conditions over Memorial Day weekend, so Paul was hopeful the scab risk may be reduced for wheat fields flowering during mid to late week.
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.
Stephen Wegulo, University of Nebraska plant pathologist, says it's recommended that a fungicide be applied at early flowering to suppress scab in scab-prone areas of Nebraska. He says the Prosaro and Caramba are good in suppressing scab and very good to excellent in controlling foliar diseases.
Wegulo also notes that timing of fungicide application for scab suppression is critical. Early flowering is the optimal time, he says, adding that once bleached heads appear scattered in the field, it's 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, Wegulo says you should 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," Wegulo says. "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.