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Issue No. 3, Article 8/April 20, 2012

Fusarium Head Blight (Scab) of Wheat--Risk Assessment and Management

Wheat plants are beginning to head out and flower in parts of southern Illinois. During this critical developmental period, wheat becomes susceptible to infection by Fusarium graminearum, the causal agent of Fusarium head blight (FHB, also known as scab. This disease can cause reduced grain yield, test weight, and quality. In addition, the fungus can produce toxins that will contaminate grain, such as deoxynivalenol (DON, also known as vomitoxin). Harvested grain with high levels of DON may be discounted or rejected outright at the elevator. To achieve the best management of FHB, different management practices must be implemented, such as planting wheat into fields that were previously cropped to soybean (rather than corn), planting wheat varieties with moderate to high levels of resistance to FHB, and applying foliar fungicides with proper timing. Of these practices, applying foliar fungicides is the only one that can be done during the growing season and is my focus here.


Symptoms of Fusarium head blight (scab) of wheat.

Multiple fungicides are registered for use on wheat, but only a few have efficacy in managing FHB. Fungicides available for FHB management all belong to the triazole class; they are Caramba (BASF Corporation), Prosaro (Bayer CropScience), Proline (Bayer CropScience), and products that contain tebuconazole as their solo active ingredient (such as Folicur). Of these products, the best efficacy has been obtained with Prosaro and Caramba.

Proper application timing is critical to achieving the best efficacy with a fungicide. The best timing is considered to be when plants are beginning to flower (early anthesis--Feekes growth stage 10.5.1), but some efficacy may still be achieved slightly before or after Feekes 10.5.1 (Table 1). In regards to timing, it is important to always follow the label recommendations and to consider the preharvest interval requirements. (The requirement for Caramba, Prosaro, Proline, and tebuconazole products is 30 days.)

Table 1. Effect of fungicide application timing on Fusarium head blight (FHB) control in Illinois wheat.

Fungicide

Application timing

FHB (% control)*

Prosaro at 6.5 fl oz

Feekes 10.5

35 b

Feekes 10.5.1

59 a

5 days after Feekes 10.5.1

37 b

Caramba at 13.5 fl oz

Feekes 10.5

38 b

Feekes 10.5.1

61 a

5 days after Feekes 10.5.1

36 b

Results represent data collected from Dixon Springs in 2009 and Brownstown, Carbondale, Dixon Springs, and Urbana in 2010.
*Values followed by the same letter are not significantly different, with 95% confidence.


Screen capture of the Fusarium head blight risk assessment tool from April 18, 2012.

When deciding if a fungicide application is needed, be sure to assess FHB risk. A risk assessment tool is available at www.wheatscab.psu.edu. The risk, which is based on weather conducive for FHB, should be assessed for each field as heads begin to develop in anticipation of flowering. According to the risk map, the current risk of FHB is low for all of Illinois, but continue to monitor the map if heads are not yet visible in your area.--Carl A. Bradley

Author:
Carl A. Bradley

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