Stripe Rust Update 5/23/12

May 23, 2012

Xianming Chen
Wheat Stripe Rust in eastern Washington and eastern Oregon

Yesterday, I was checking wheat fields in Whitman, Columbia, Walla Walla, Benton, Franklin, and Adams counties of Washington and the Pendleton and Hermiston areas in Umatilla county of Oregon. Winter wheat ranged from late jointing (Feekes 9) to flowering (Feekes 10.5) with most fields at boot (Feeks 10) to heading (Feeks 10.2). Spring wheat ranged from not emerged to early jointing stage (Feekes 4). In commercial fields, stripe rust was found in all of the above counties, except Whitman Co. In one of our experimental fields near Pullman (Whitman Co.), I was only able to find two leaves with just started stripe rust pustules in susceptible spreader rows, indicating the starting of stripe rust in the Palouse region. This starting time is about a week later than normal for this location. In Columbia Co., stripe rust was found about two out of ten checked fields. In Walla Walla Co., stripe rust was found about four out of ten fields. However, the disease developed to 40% severity in susceptible spreader rows and some entries in our stripe rust monitoring nurseries near Walla Walla, where stripe rust was found to be just started a month ago. In Umatilla Co., stripe rust was found in two fields near Milton and one field near Pendleton and was not found in about other four or five fields checked. Very low levels of stripe rust was found in fields of Pendleton and Hermiston stations. Stripe rust was found in every checked field in the Horse Heaven Hills region in Benton Co., near Connell and Kahlotus in the Franklin Co., and along HW 26 in the Adams Co. Overall, the incidences (less than 1% to 5%) and severity (1 to 10%) of stripe rust were low. Most infected leaves are upper leaves with just a single stripe, and only one hotspot of 1 foot in diameter with infection from the bottom to the top was found in a field with plants at flowering stage north of Walla Walla, indicating overwintering.

Other Problems

Physiological leaf spot (PLS) was a common problem in winter wheat fields in Columbia, Walla Walla, and Umatilla counties. Crown rot was severe in Horse Heaven Hills. Barley yellow dwarf (BYD) was common in early planted fields. Some fields had herbicide damage. These problems caused spots (PLS), yellowing or dead leaves (crown rot, BYD, herbicide damage) in patches or stripes in fields, which can be confused with stripe rust in distance. Please make sure to distinguish them from stripe rust as fungicides controlling stripe rust have no effect on these problems.

Weather Conditions Related to Stripe Rust

The current stripe rust pressure is relatively low, compared to the same time of both 2010 and 2011, but will increase quickly during the next two to three weeks based on spore availability and weather conditions in the last three weeks and forecasted for the next 10 days. The average temperature in May so far has been and is predicted for the entire May to be lower than normal (more favorable for infection and little bit less favorable for producing spores), but the precipitation has been and is predicted to be lower than normal in May (less favorable for infection). However, the widespread rains and showers this week should increase stripe rust infection. The low temperatures this week and forecasted for next week are not high enough for high-temperature adult-plant (HTAP) resistance to work at its best.

Recommendation for Control of Stripe Rust

Winter wheat. As winter wheat in most fields are approaching flowering stage, from now to next couple of weeks will be critical for fungicide application. The previous general recommendation remains the same for wheat cultivars in different reaction categories. The following winter wheat cultivar in the susceptible or moderately susceptible categories may need fungicide spray: AgriPro Paladin, Eddy, Esperia, Whetstone, Declo, WB-Tucson, AP Legacy, Tubbs 06, UICF Brundage (CLEARFIELD®), Boundary, Mary (OR2040726), and Xerpha. The following cultivars in the resistant category may not need fungicide application: Norwest 553, Legion, Madsen, Skiles, Bruehl, Cara, Chukar, and Coda. The following moderately resistant cultivars may or may not need spray depending upon stripe rust situation: Bauermeister, Finley (used to be susceptible, but was resistant in the last two years due to race changes, better to spray this year), MDM, UICF Grace, UI Silver, AP700 CL (CLEARFIELD®), ARS-Amber (ARS960277L), Brundage 96, Bruneau, Eltan, Masami, ORCF-102 (CLEARFIELD®), ORCF-103 (CLEARFIELD®), Rod, Stephens, WB-528, ARS-Chrystal, and ARS-Crescent. It is very important to check your fields, no matter which categories of the cultivars, and apply a registered fungicide at the full rate when stripe rust reaches 1 to 5% incidence with active rust spores. Hopefully, one time application between boot and flowering stages can provide adequate control, depending upon the weather conditions in June.

Spring wheat. Early planted spring wheat is approaching the stage for herbicide application. For susceptible and moderately susceptible cultivars (Nick, Hank, Tara 2002, Macon, Otis, Alpowa, Babe, Bullseye, Hollis, Jefferson, and Westbred 926), it may be better to spray with fungicide together with herbicide. For resistant and moderately resistant cultivars (JD, Clear White, Diva, Louise, Wakanz, Whit, Eden, Buck Pronto, Kelse, Scarlet), it may be unnecessary to spray with fungicides.

Wheat Stripe Rust in the Nation

In the recent weeks, wheat stripe rust has spread quickly in states east of the Rocky Mountains from south to north and reached North Dakota, Minnesota, Wisconsin, and Ontario, Canada, making this year one of the most distributed stripe rust years, almost like the year 2010. So far this year, wheat stripe rust has been reported in 21 states: Arkansas, Mississippi, California, Texas, Louisiana, Tennessee, Kentucky, Oklahoma, Oregon, Washington, Kansas, Georgia, Illinois, Indiana, Nebraska, North Carolina, Virginia, Missouri, Minnesota, North Dakota, and Wisconsin.

Barley Stripe Rust

Barley stripe rust has been found in California, western Oregon, and western Washington.

Rust on Barberry

On May 14, pycnia (presumably stem rust) were found on leaves of a barberry bush near Potlatch in northern Idaho, the appearance time is similar to last year and about a week later than normal.