Winter wheat is at or near to the flag leaf (Feekes 8) growth stage throughout the state. This is an important time to actively scout wheat fields to most effectively determine if the use of a foliar fungicide will be needed. The main diseases we have seen so far this spring include Septoria leaf blotch, powdery mildew, and tan spot. We have addressed those three diseases, plus other foliar diseases in the April 10 Wisconsin Crop Manager. So far this year, the incidence and severity of these three diseases have been quite variable and dependent on the wheat variety and environment. With susceptible wheat varieties, we have seen incidence for Septoria leaf blotch and powdery mildew as high as 100% in some of our plots. 

 

It is during flag leaf emergence that questions need to be asked to determine if foliar fungicide use should be accomplished.  To help guide that decision-making process, there are four questions that should be asked (Beuerlein 2001; Miller 1999):

If the answer to the first three questions is “yes”, and the answer to the last one is “no”, then application of a foliar fungicide will most likely be warranted. Besides identifying the foliar diseases in wheat, it is important to understand if the disease pressure is increasing. In Figures 1 and 2, two example sets of standard area diagrams are presented, the first for rust and the second for powdery mildew. These can be used to help determine the amount of disease observed on the leaves. Furthermore, if it is appears that the disease is moving into the upper canopy, this would be another indicator that the disease is increasing.

Figure 1. Example set of standard area diagrams for wheat rust illustrating 5, 15, 25, and 50% leaf severity. Images created using Severity.Pro software.

 

Figure 2. Example set of standard area diagrams for powdery mildew illustrating 5, 15, 25, and 50% leaf severity. Images created using Severity.Pro software.

 

For further information regarding foliar fungicides available for wheat, consult Pest Management in Wisconsin Field Crops, UW-Extension A3646. For up-to-date information regarding the current status of rust of wheat or barley, consult http://www.ars.usda.gov/Main/docs.htm?docid=9757. For real-time forecasting for the risk of Fusarium head blight, consult http://www.wheatscab.psu.edu. Finally, for the most up-to-date information regarding wheat development and wheat diseases in Wisconsin, consult http://thesoyreport.blogspot.com.

 

References:    

 

Beuerlein, J. E. 2001. Wheat Growth Stages and Associated Management. The Ohio State University Extension, AGF-126-01.

 

Miller, T.D. 1999. Growth Stages of Wheat: Identification and Understanding to Improve Crop Management. Texas Agricultural Extension Service, SCS-1999-16.