Rust Update 5/20/10

May 20, 2010

Xianming Chen
Stripe rust shows up in the Palouse Region

Yesterday, we were checking for stripe rust in the Palouse region (Whitman County, southeastern WA). Winter wheat was in the middle of jointing stage (Feekes 6-8). Stripe rust (both susceptible and resistant reactions) was found in several commercial fields and susceptible checks in our experimental plots. The incidents were very low (less than 0.1%). Stripes or patches were generally less than 3 cm. Most infected leaves were at the low canopy, indicating that rust overwintered. The time of this first stripe rust observation was similar to 2008 (May 17), but earlier than 2009 (June 2).

Stripe rust has been developing rapidly in Walla Walla and nearby regions

Since the first observation in our experimental plot in Walla Walla on April 29, stripe rust has been reported to be widely spread. Plants of a field of ‘Declo’, a susceptible hard red winter wheat cultivar, were quite uniformly infected. Up to 20% incidence was reported in some fields grown with ‘Tubbs 06’ or a mixture of ‘Rod’ and ‘Tubbs 06’. Dr. Stephen Guy reported significant infection in one replication of ‘Lambert’ in the variety trial near Walla Walla. Some fields have been sprayed with fungicides in this region. Rust is developing in the Central Ferry area (Columbia County, southeastern WA). Based on Dr. Kim Campbell, ‘Xerpha’ (a soft white winter wheat with a moderate level of high-temperature adult-plant resistance) had infection type 5 and 10-20% severity. Rust has been reported in commercial fields in this area.

Stripe rust has been severe in western WA and western Oregon

Stripe rust reached 70-80% severities on susceptible entries in our plots at Mt. Vernon by the last week of April, which was quite normal for that region. Based on Dr. Chris Mundt, stripe rust has been developing in the Milwaukie Valley since March. Cultivar ‘Goetze’ got heavily infected. Growers have already sprayed fields with fungicides once or twice. Stripe rust was just reported this week at the Pendleton Experiment station in northeastern Oregon.

Aecia developed on barberry bushes in the Palouse region

Yesterday, we were checking rust on barberry bushes in Moscow and near Potlatch, Idaho (Latah County) and Colfax, Washington (Whitman County). Rust (presumably most of stem rust) infection on barberry bushes reached the early aecial stage. The bushes near Potlatch were heavily infected, almost every leaves were infected with multiple rust pustules, similar to last year. No rust was found in the nearby winter wheat field (too early for wheat, as stem rust was first found in the nearby winter wheat field in mid June last year). Every of other bushes got infected, but much light than the Potlatch bushes. The barberry bushes were in the later bud to flowering stages. Based on the current rust situation, we predict the similar level of stem rust on wheat and barley to last year.

Stripe rust nationwide

Nationwide, stripe rust of wheat has been reported in California, Texas, Louisiana, Arkansas, Mississippi, Oklahoma, Kansas, Colorado, Nebraska, South Dakota, Illinois, Indiana, Wisconsin, Virginia, Oregon, and Washington. More damage will occur this year than the last three years. The long period of low temperature and high moisture conditions in the south-central states and other regions, such as western Oregon, has been very favorable for stripe rust development and not favorable for expression of high-temperature adult-plant resistance in some of the cultivars.

Stripe rust management in the PNW

The current stripe rust situation is similar to what we forecasted in January, little bit more severe than last year, but should be less than 2005. The low temperature and high moisture conditions in the past several weeks and predicted for the next two weeks have been and will be favorable for stripe rust. Under such conditions, fields grown with susceptible cultivars (such as Declo, Buchanan, Finley, Finway, Palatin, and Eddy) should be sprayed. Depending upon locations, cultivars with low to moderate levels of high-temperature adult-plant resistance (such as Farnum, Xerpha, and Baurmeister) may need to consider spraying. Cultivars with high levels of resistance (such as Eltan, Madsen, Stephens, and many others) may not need to spray. Now is the critical time for growers in the Walla Walla, central WA, and nearby regions to check their fields and spray if necessary. Growers in the Palouse region (Whitman County of Washington and Latah county of Idaho) and further north should start to check wheat fields, and consider spraying if rust develops to 5-10% of severity. People also need to consider the fact that several cultivars (such as Tubbs, Tubbs 06, Brundage 96, and many others) are not uniformly resistant, susceptible plants can be found in these crops. Fields grown with such cultivars may need or not need spraying depending upon locations, and a 20% severity threshold may be used to make decision.