Managing Fusarium Head Blight (Scab) of Wheat
Department of Crop Sciences
Extension Plant Pathologist
Small Grains Breeder
Department of Crop Sciences
Fusarium head blight (FHB), also known as “scab”, is a disease of wheat that can cause both yield and quality losses. Symptoms of FHB appear as “bleached heads” or heads with both green and bleached areas. The fungus, Fusarium graminearum (a.k.a. Gibberella zeae) causes FHB of wheat and can cause Gibberella stalk and ear rot of corn. The fungus also produces the toxin deoxynivalenol (DON) that can contaminate grain, which can be a serious problem for millers. Weather is an extremely important factor involved in the development of FHB, especially from flowering through kernel development. Moderate temperatures (75 to 85°F), prolonged periods of high humidity, and prolonged wet periods favor FHB development.
Successfully managing FHB requires an integrated approach, where the use of resistant varieties, better crop sequences, and fungicides can limit losses due to FHB:
Resistant varieties: Although no varieties are immune to FHB, some are more resistant than others. The University of Illinois Winter Wheat Breeding Program has been developing wheat varieties with partial-resistance to FHB. In addition, the University of Illinois Wheat Breeding Program has been rating wheat varieties for FHB severity under high-pressure FHB environments over multiple years. These ratings are available on-line at the University of Illinois Variety Testing site, located in the “Small Grains” section (http://vt.cropsci.illinois.edu).
Cropping sequence: Because corn stubble can harbor the FHB fungus, wheat following soybean is at a lower risk of developing FHB than wheat following corn.
Foliar fungicides: The use of a foliar fungicide is the only “in-season” option for control of FHB. Although fungicides are a good control option, losses will still occur on a highly-susceptible variety sprayed with a fungicide in an environment conducive for FHB; therefore, it is always important to start off on the right foot and plant a variety with good resistance to FHB. In 2007 and 2008, new registrations occurred making more fungicides available for control of FHB in wheat. These include Proline (prothioconazole; Bayer CropScience), Folicur (tebuconazole; Bayer CropScience) and Caramba (metconazole; BASF).
For control of FHB, fungicides should be applied at Feeke’s growth stage 10.5.1 (early anthesis). It is also important to spray with nozzles oriented to spray forward, which helps coverage of the wheat head. In the past, recommendations were to use nozzles that sprayed both forward and backward; however, recent research out of North Dakota State University has shown that “forward-facing” nozzles may be all that are needed.
Fungicides that contain an active ingredient in the “strobilurin” class should NEVER be applied to control FHB. This includes products like Headline, Quadris, Quilt, and Stratego. Research has shown that strobilurin fungicides can actually increase DON levels in harvested grain. These strobilurin products are very good at controlling foliar diseases of wheat, and if used, should be applied earlier in the season.
Forecasting system for FHB. To help with fungicide application decisions, an FHB forecasting system is available. The Fusarium Head Blight Risk Assessment Tool is available on-line at www.wheatscab.psu.edu. A “risk map” is available that allows you to see what your risk of FHB is throughout Illinois. This risk is based on weather conditions that occurred just before flowering.