Stripe Rust Update 5/3/13

May 3, 2013

Xianming Chen
Wheat stripe rust in Washington and Northeastern Oregon

We were checking wheat fields in Washington and northeastern Oregon on April 30 – May 3.
Winter wheat ranged from Feeks 5 to 9. In the Palouse region of Washington (Whitman Co.),
very low level of stripe rust was found in commercial winter wheat fields west of Colfax. In our
experimental fields near Pullman, stripe rust was found on low leaves (indicating over-wintered
infection) actively producing spores, and incidences were less than 1% in the highly susceptible
variety.

In Central Ferry (Garfield Co.), stripe rust of about 2% incidence was found with up to 20%
severity on some leaves. Small hot spots (about 1 foot in diameter) were apparent.

In Columbia County, stripe rust of low incidence (less than 1%) and low severity (less than 2%)
was found in some winter wheat fields along highway 12.

In Walla Walla County, stripe rust developed up to 60% severity and 80% incidence in
susceptible checks in our winter wheat nurseries. Stripe rust was also found on first leaves of
spring wheat plants at Feeks 2. Low stripe rust was found in commercial fields and also reported
by growers.

In Franklin County, low stripe rust was found in winter wheat fields between Connell and
Kahlotus. Similar low levels of stripe rust were also found along highway 26 in Franklin
County.

In western Washington, stripe rust developed up to 80% severity on susceptible entries of our
winter wheat nurseries at Mt. Vernon. Relatively low stripe rust with mostly resistant reactions
was found in some commercial wheat fields.

Barley stripe rust was found up to 40% severity on some winter barley entries in our
experimental nurseries at Mt. Vernon.

In northeastern Oregon, no rust was found in winter wheat fields at the Pendleton station and
nearby commercial fields. Stripe rust was easily found on some winter wheat entries at the
Hermiston station. Stripe rust of resistant to moderately resistant reactions was found on triticale
plants. No rust was found on barley plants at both the stations.

As previously recommended, fungicide application together with herbicides is needed for fields
grown with susceptible or moderately susceptible varieties for both winter and spring crops.
Many winter wheat fields have been sprayed with fungicides. If the first spray was done about a
month ago, it is necessary to start checking the field again. If stripe rust starts developing,
second fungicide application may be needed. As the weather has switched from cold to warm in
this week and will continue warming up in the next two weeks, stripe rust will be likely
developing faster in the next couple of weeks. Based on the long-term forecast of weather conditions for May and the summer (above normal) for the Pacific Northwest, we expect that high-temperature adult-plant resistance will likely work better this year than in the past three years.

Wheat stripe rust in other states

In addition to Washington, wheat stripe rust has occurred in Arkansas, Texas, Louisiana, Mississippi, California, Oregon, Oklahoma, Georgia, Kansas, Tennessee, South Carolina, and Kentucky. Fungicides have been used to control stripe rust in these states.