June 2, 2008

Although rust diseases have not appeared in most of the state, the potential still exists for outbreaks of leaf rust and stripe rust. In south central and eastern Nebraska wheat is already flowering or will be flowering very soon. This means that the window for applying certain fungicides for control of foliar diseases is past.

If a fungicide was not applied before flowering to protect against foliar diseases, the best strategy in south central and eastern Nebraska is to apply a fungicide for suppression of Fusarium head blight (scab). The fungicides labeled for suppression of fusarium head blight also can control rust diseases (Folicur®); rust diseases and leaf spots (Proline™); or rust diseases, leaf spots, and powdery mildew (Caramba™ and Tilt®). None of these fungicides should be applied within 30 days of harvest.

Elsewhere in the state where the flag leaf is just emerging or emerged within the last several days, such as in the northern Panhandle, apply any fungicide labeled for rust to protect the flag leaf. In the Panhandle, the risk for rust diseases is higher in irrigated than in dryland fields.

In general, apply a fungicide to protect against rust diseases according to the following criteria:

• Irrigated wheat (Panhandle)
• Rainfall is forecast
• A susceptible variety is planted
• Yield potential is 40 bu/ac or more for dryland wheat and 70 bu/ac or more for irrigated wheat. (These thresholds may be lower if wheat was locked in at prices higher than $6/bu).
• The time to harvest is 30 days or more

Also see Preparing for Rust Diseases in Winter Wheat in the April 13, 2007 CropWatch.

Stephen Wegulo
Extension Plant Pathologist