Time to Watch Closely on Spring Wheat Fields for Stripe Rust and Apply Fungicides
Xianming Chen
Stripe rust is developing rapidly in susceptible spring wheat fields in eastern Washington. On June 12, various levels of stripe rust were found in spring wheat fields in Adams and Whitman counties. In some fields, more than 60% of plants had stripe rust with severity levels up to 20%. These fields are producing abundant rust spores, which can accelerate rust infection in the same fields and other fields in the region. Because stripe rust occurred earlier in this year than that of last year, do not wait until flag leaves have rust to use fungicide. Because the weather will still be favorable to stripe rust in the next 10 days, the disease will be more severe in susceptible spring wheat fields. At this time, if you find 5% or more plants with rust and 5% rust severity (percentage of rusted leaf surface on infected leaves), you should consider applying fungicide.
The shattering problem of Zak also can contribute to stripe rust epidemic. Because last winter was mild, volunteer Zak plants survived the winter well in some fields. It has been reported that about 20% plants with stripe rust in a winter wheat field grown with mixture of Madsen and Rod this year in Columbia County are Zak plants. In the long-run, practices that help to reduce susceptible volunteer plants can delay and reduce rust infection.
Stripe rust also is increasing rapidly on susceptible winter wheat varieties in experimental plots. On June 12, our irrigated plots had over 50% rust at the Lind location. Near Pullman, susceptible entries had up to 60% stripe rust in disease nurseries. Most commercial winter wheat fields did not have much rust because of resistant varieties. In both experimental plots and some fields, the club wheat Edwin had about 10% stripe rust, but mostly with intermediate reactions.
Barley stripe rust is increasing in experimental plots. But, only trace stripe rust was found in fields grown with Baronesse in the Palous region. This year, stripe rust may not be a big problem in most barley fields because of moderately resistant varieties grown in eastern Washington. However, fields grown with susceptible varieties, such as Steptoe, Harrinton, and Morex, should be watched closely.
So far, leaf rust and stem rust have not been found yet.
If you have any questions about stripe rust and other rusts, please contact me at 509-335-8086 (e-mail: xianming@mail.wsu.edu).