Stripe Rust Update, June 16, 2017

Xianming Chen

Wheat Stripe Rust

In the Pacific Northwest, winter wheat in most areas has passed the flowering stage.  Thanks to planting of resistant varieties and widely use of fungicides in the early season with some fields sprayed twice, stripe rust in most fields of winter wheat is under control.  Depending upon areas and various times of planting, spring wheat crop varies from Feekes 4 to Feekes 10.5.3.  Stripe rust has developed rapidly in spring wheat fields with severity on susceptible varieties ranging from 5% to 100% depending upon area and planting date.

Because the cooler weather and good moisture in this week, stripe rust will likely develop more in the next couple of weeks. For fields of moderate susceptible and susceptible varieties (stripe rust ratings 5 – 9) of winter wheat, fungicide application is needed if the crop has not passed Feekes 10.5 and fungicide was applied more than two weeks ago.  For spring wheat, fungicide is needed at the time of herbicide application for fields planted with moderately susceptible and susceptible varieties if not done so.  For fields of fungicide applied about three weeks ago, another application is needed.  For varieties previously reported to be resistant to moderately resistant (ratings 1-4), check fields and consider fungicide application if active rust pustules are seen and severity reaches 5%.

We took stripe rust notes in our experimental fields of spring wheat on June 15, most plants passed the flowering stage and the susceptible check had 100% severity. Table 1 shows the data and ratings for the spring wheat variety trials for reference.  As these data were from only Lind and rust races can be different in different areas, use these data together with the data from the last year for considering to use or not to use fungicides.

Since the last report on May 19, wheat stripe rust has been reported in South Dakota, Minnesota, North Dakota, and New York in addition to the previous reports in Texas, Louisiana, Arkansas, Mississippi, North Carolina, Oklahoma, Kansas, Washington, Oregon, Wisconsin, Virginia, Delaware, Tennessee, Michigan, Kentucky, Nebraska, Indiana, Georgia, Idaho, Arizona, California, Montana, and Colorado.  Wheat stripe rust has been reported in Alberta, Ontario, and Manitoba provinces of Canada.

  Barley stripe rust

In our spring crop nurseries at Lind (Adams County, WA), stripe rust was uniform on susceptible varieties with severity up to 40%.  For this dryland area, this is the most severe barley stripe rust we have seen in the last 20 years, partially due to the 6-inch higher-than-average precipitation this year, although much lower than wheat stripe rust in this location.  Barley stripe rust has not been observed in the Palouse region yet.  In addition to Washington, barley stripe rust has been reported in California and Oregon.

Fungicide application may be needed to control barley stripe rust this year.  Check barley fields for stripe rust, if severity reaches 5%, apply fungicide.  The fungicides that control wheat stripe rust also control barley stripe rust.

Table 1.  Stripe rust data of the 2017 WSU Spring Wheat Variety Trials at Lind, WA*

* IT = infection type; % = severity based on infected leaf areas; and ratings are in a 1-9 scale with 1 for most resistant and 9 for most susceptible.