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Fungicides help control foliar disease in wet wheat

This year's growing season follows a fairly wet winter for Nebraska and much of the Plains, and continued wet conditions this spring will affect the development of foliar diseases in wheat. The risk of disease development is higher in irrigated than in dryland wheat, especially in areas that usually receive less than adequate rainfall.

The major fungal diseases likely to develop early in the growing season are powdery mildew and tan spot. Powdery mildew usually is more prevalent in the eastern half of Nebraska while tan spot can occur throughout the state. Development of leaf rust and stripe rust will depend on when spores wind-blown from southern states arrive in Nebraska. Stripe rust has occurred sporadically since 2000.

Fungicide applications are aimed at maximizing green leaf area of the top leaves during grain fill. In wheat, the flag leaf contributes the most to grain fill, followed by the flag-1 leaf. Therefore, to maximize yields, fungicide applications should be timed to protect the flag leaf.

The fungicides used to control foliar diseases of wheat in Nebraska include Headline (pyraclostrobin), Quadris (azoxystrobin), Quilt (azoxystrobin + propiconazole), Stratego (trifloxystrobin + propiconazole), Tilt (propiconazole), PropiMax (propiconazole), Dithane (mancozeb), and Manzate (mancozeb).

In general, it is economical to apply a fungicide only if the return from fungicide application exceeds the cost of buying and applying the fungicide. A general rule is that yield potentials should be 40-50 bu/ac for dryland wheat and 75 to 85 bushels per acre for irrigated wheat for a fungicide application to be profitable. The higher the price of wheat, the more profitable a fungicide application be.

If conditions are favorable for disease development early in the season, it may be beneficial to apply a fungicide for early season disease suppression and follow up with a second application at flag leaf emergence. If a decision is made to apply two or more sprays, care should be taken not to exceed the maximum product rate for a single growing season. Also adhere to restrictions on the interval between two spray applications.

Results from fungicide efficacy trials may vary with location and year.

This year's growing season follows a fairly wet winter for Nebraska and much of the Plains, and continued wet conditions this spring will affect the development of foliar diseases in wheat. The risk of disease development is higher in irrigated than in dryland wheat, especially in areas that usually receive less than adequate rainfall.

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