No. 3 Article 4/April 11, 2008

Managing Fusarium Head Blight (Scab) of Wheat

Fusarium head blight (FHB), also known as scab, is a disease of wheat that can cause both yield and quality losses. Symptoms appear as bleached heads or heads with both green and bleached areas. The fungus Fusarium graminearum (aka Gibberella zeae) causes FHB of wheat and can cause Gibberella stalk and ear rot of corn. The fungus also produces the toxin deoxynivalenol (DON), which can contaminate grain, a serious problem for millers. Weather is extremely important 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.

A wheat head infected with the Fusarium head blight fungus (photo C.A. Bradley).

Successfully managing FHB requires an integrated approach, where the use of resistant varieties, better crop sequences, and fungicides can limit related losses.

Resistant varieties. Although no wheat varieties are immune to FHB, some are more resistant than others. Dr. Fred Kolb's wheat-breeding program at the University of Illinois has rated varieties for FHB severity under high-pressure FHB environments over multiple years. These ratings are available online at the University of Illinois Variety Testing site, located in the "Small Grains" section.

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, so it is always important to start off on the right foot and plant a variety with good resistance.

As of today (April 9, 2009), the only fungicides that have Fusarium head blight on their labels are Proline (Bayer) and Tilt (Syngenta). Proline has a 30-day preharvest interval, while Tilt's is 40 days. A summary of FHB fungicide trials conducted across multiple years and states was presented at the U.S. Wheat and Barley Scab Initiative Forum last fall by Dr. Pierce Paul of Ohio State University. In his summary, Proline was significantly better than Tilt at reducing FHB severity and reducing DON levels in harvested grain. There is a slight chance at this point that additional fungicide products will still receive registration for use on wheat to control FHB this spring; I will address the additions in another Bulletin article if that occurs.

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 in coverage of the wheat head. Past recommendations said to use nozzles that sprayed both forward and backward; however, recent research at 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, including products like Headline, Quadris, Quilt, and Stratego. Research has shown that strobilurin fungicides can actually increase DON levels in harvested grain. These products are very good at controlling foliar diseases of wheat, and if used they should be applied earlier in the season (around Feekes 8--see issue 1, March 21, 2008, of the Bulletin).

Forecasting system for FHB. The Fusarium Head Blight Risk Assessment Tool is available to help with fungicide application decisions. A "risk map" shows the risk for FHB throughout Illinois based on weather conditions to date.

Screen capture of the Fusarium Head Blight Risk Assessment Tool from May 2007.

--Carl Bradley

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