Fungicide applied along with herbicides on tillering wheat might give a farmer greater peace of mind but it isn’t likely to increase yields, according to research by South Dakota State University.

While not a costly input, fungicides often are unnecessary on tillering wheat because the crop usually is under little disease pressure at that growth stage, said Emmanuel Byamukama, a SDSU plant pathologist.

“Diseases such as tan spot, powdery mildew and stagonospora/septoria leaf blotch pathogens survive on crop residue and develop and become severe when the canopy starts to close in,” Byamukama said. “This is when more moisture is trapped under the canopy and there is poor air circulation. These conditions promote the development of leaf spot and powdery mildew. Usually at tillering, the undergrowth is not yet too dense to promote disease development.”

Wheat straw with tan spot fungus  (SDSU photo)

In circumstances where wheat follows wheat, susceptible wheat cultivars have been planted or excessively wet conditions exist in the spring, applying fungicide with herbicides can contribute to higher yields.

“Weather conditions do influence the level of disease development and, therefore, influence yield gain resulting from fungicide application,” Byamukama said.

“Research done at SDSU shows a strong relationship between rainfall in the month of May and the yield gain between early strobilurin-treated plots and non-treated winter wheat plots. More rainfall in May was associated with higher yield gain from a strobilurin fungicide application. Although this is not an extensive data set – two sites, three years – it shows the likelihood of seeing profit when there is higher spring precipitation.”

When deciding whether to apply fungicide to wheat, farmers should consider weather conditions, the type of crop residue in their fields and field conditions conducive to disease development. Scouting is a must, Byamukama said.

The SDSU Plant Pathology Extension program has partnered with the North Dakota State University small grains program to develop a small grains disease forecasting system. The online tool , of most use to farmers in the Great Plains, is based on weather conditions.

Farmers using the online tool can enter a SDSU weather station nearest their crop and the crop’s growth stage to determine the likelihood that their crop could develop tan spot, stagonospora nodorum blotch and Fusarium head blight.

By Steve Leer

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