As we were checking wheat fields on April 20, we found stripe rust in Horse Heaven Hills and Walla Walla. In both areas, stripe rust was just starting in early planted winter wheat fields. Some plants in small hotspots (less than one foot in diameter) had rust from the bottom to top leaves, indicating that stripe rust had over-wintered in these early planted fields. We did not find stripe rust in late planted fields in these areas. The last Thursday observations and the report in the early week clearly indicated the occurrence of stripe rust in south central and south eastern Washington. The occurrence of stripe rust in these areas was much later than that of the last year, but the starting time is about normal. The disease could develop and spread rapidly from now on depending upon the weather conditions. Start to check your fields frequently for stripe rust. If you grow susceptible cultivars under irrigation and/or have high yield potential, you may consider applying fungicides when you see about 10% rust severities and second application may be needed before the heading stage. For most rain-fed fields of susceptible and moderately susceptible cultivars, one time foliar application may be profitable and adequate, which should be between boot to heading stage.
Today, I received a report of stripe rust found in an ‘Eltan’ field near Odessa, Washington, which needs to be confirmed. Last year, Eltan became more infected, indicating that the all-stage (also called seedling resistance) is no longer effective. However, the high-temperature adult-plant (HTAP) resistance in Eltan is still effective. Therefore, stripe rust can occur on seedlings of Eltan, but HTAP resistance will be more and more effective as plants grow older and the weather becomes warmer.
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