Wheat Disease Report

Over the last week, I conducted surveys in the following areas: Larned to Salina, Hill City to Garden City, and Garden City to Eureka. The wheat is greening up nicely in most fields. Based on the amount of precipitation in most areas, this could be a very good year with respect to yield. However, diseases are present that warrant attention. Leaf rust, powdery mildew, and speckled leaf blotch (Septoria) are all active on the lower leaves in central Kansas. Leaf rust and speckled leaf blotch are active in western Kansas; I didn’t see any powdery mildew in the western counties. Although present on the older leaves, I verified in the lab that the spores of these three pathogens are viable. This indicates that these pathogens likely survived the winter in Kansas and we might expect disease development earlier than last year. This is consistent with reports from the states to our south including Texas and Louisiana where they have begun spraying for protection against leaf rust (and in a few fields stripe rust) approximately four weeks earlier than usual. By all accounts, there will be high leaf rust pathogen pressure this growing season and producers should be prepared. This means having contingency plans to spray with fungicides if leaf or stripe rust hits the flag leaves early. Bob Bowden prepared a table that indicates as little as 25% leaf rust severity on the flag leaf at flowering can result in a 15% yield loss. The weather during the course of the growing season will determine whether an epidemic develops but preparedness is the key to minimize impact.

In light of all the concern for soybean rust throughout the U.S. and the fact that the only real management option is fungicide application, it is possible that precautionary purchases for soybean rust may affect the availability of certain fungicides. Have producers line up a source now, not the week they need product and application.

In the clinic we have received samples from central Kansas that tested positive for both Wheat Soilborne Mosaic Virus and Wheat Spindle Streak Virus. I also collected samples from fields in western Kansas with symptoms consistent with virus disease; lab assays will be run to determine which viruses are present. As the temperatures increase, the symptoms should decrease. There are significant variety differences in susceptibility to these viruses. Additionally, one sample with serious root and crown rot (appeared to be Fusarium, still testing) was submitted from south central Kansas.

James Stack
Extension Specialist
Plant Pathology Program

E-mail: jstack@plantpath.ksu.edu

Phone: (785) 532-5810

FAX: (785) 532-5692
http://www.oznet.ksu.edu/path-ext

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Web updated 9/01/06
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