Predicting Risk of Fusarium Head Blight (Scab) in Wheat

Kiersten Wise, Assistant Professor of Field Crop Diseases, Department of Botany & Plant Pathology, Purdue University

Wheat in far southern Indiana reached flowering (Feekes growth stage 10.5.1, Figure 1) this week, and wheat throughout southern Indiana is in late boot stage or beginning to head. Wheat in central to northern Indiana is still variable, ranging from early boot to just past jointing (Feekes 7). In southern Indiana this is an important time to consider the risk for Fusarium head blight development in wheat.

The fungus that causes head scab, Fusarium graminearium, infects the wheat plant during flowering, or Feekes growth stage 10.5.1. Rainy, warm, and humid weather conditions favor disease development. Symptoms include bleached spikelets on the head (Figure 2), and small or shriveled grain kernels, commonly called “tombstones”. The fungus also produces hazardous toxins, such as deoxynivalenol, or DON, which can accumulate in the infected grain. DON is toxic to livestock, especially swine, and grain with DON levels between 1 and 3 ppm can reduce weight gain in animals. DON-infected grain may also be subjected to dockage or refusal, depending on the grain buyer.

Crop rotation and selection of partially resistant varieties can help prevent Fusarium head blight development, but timely fungicide applications may be needed to prevent or manage the disease in-season. There are several good fungicides available for Fusarium head blight control, and these are listed in the foliar fungicide efficacy table (pdf file) developed by the North Central Regional Committee on Management of Small Grain Diseases or NCERA-184 committee.

Applications of fungicide prior to head emergence, such as those applied at jointing or flag leaf emergence may not reduce FHB infection. Also, some research has shown that fungicides containing strobilurin modes of action(Headline, Quadris, Quilt, Stratego, Twinline, etc.) increase the level of DON accumulation in FHB infected wheat (1,2). Therefore, we do not recommend applying strobilurin fungicides for Fusarium head blight control. Also, be sure to follow label restrictions on how many days must pass between fungicide application and harvest.

Fungicides are an additional input into wheat production, and are not always necessary, especially if the risk of Fusarium head blight infection is low. Fusarium head blight has not been as problematic in Indiana over the last several years; however, the frequent rains and warmer temperatures could increase the chances of Fusarium head blight development in 2009. There is an excellent risk model tool available for growers to use to assess the risk of Fusarium head blight infection in Indiana. This model can be accessed through the following link: <http://www.wheatscab.psu.edu/>. Weather conditions have been favorable for Fusarium head blight development in far southern Indiana, and growers should be checking the model to determine the approximate level of risk for their location. Additionally, it is important to scout fields in southern Indiana to determine the exact growth stage of wheat for optimum timing of any potential fungicide applications.

At this site there are several links that explain how the model was developed, and links providing additional information about Fusarium head blight on wheat. To access the model directly, click on the link marked “Risk Map Tool.” The first screen will explain how to use the model. This model requires that you know the approximate flowering date of your wheat variety, and after reading the initial screen, you can click on calendar to input the date that your variety is expected to flower. At this point, if you click on the state map of Indiana, it will take you to the local scab forecast, and you can calculate the Fusarium head blight risk level for that specific area (Figure 3).

This model uses weather information including temperature, rainfall, and relative humidity to calculate risk levels for Fusarium head blight. Although it is a good tool for predicting risk, it has an estimated accuracy level of 80%. Keep in mind that the model does not provide a guaranteed prediction for whether or not scab will occur in individual fields.

References:

C.A. Bradley, E. Adee, S. Ebelhar, and B. Young. 2008. Fungicide control of Fusarium head blight on soft red winter wheat in Illinois. In: Proceedings of the United States Wheat and Barley Scab Initiative 2008 National Fusarium Head Blight Forum p. 10. Online at: http://www.scabusa.org/pdfs/forum08_proc_complete.pdf.

C.R. Hollingsworth and C.D. Motteberg. 2008. Determining potentials for DON accumulation from prehead timing of fungicide application on spring wheat and 6-rowed malting barley in Minnesota. In: Proceedings of the United States Wheat and Barley Scab Initiative 2008 National Fusarium Head Blight Forum p. 26. Online at: http://www.scabusa.org/pdfs/forum08_proc_complete.pdf.

Click image to enlarge

Fig. 1. Feekes growth stage 10.5.1.

Fig. 2. Bleached spikelets on the head of wheat (Photo courtesy of G. Shaner).

Figure 3. Risk model predictions for Fusarium head blight development in Indiana for May 8th.