Stripe Rust Update and Forecast
Stripe Rust in the Western U.S.
In the Pacific Northwest (PNW), stripe rust this year has been much lower than the rust development in 2011, except for northwestern Washington, stripe rust developed to 100% prevalence and 60% severity on susceptible entries in experimental nurseries by the end of March as always. In western Oregon, stripe rust was observed in a couple of lines in a breeding nursery near Corvallis in the first week of April.
In eastern Washington and northeastern Oregon, stripe rust has started showing up, but still remained hard to find. Since the last update, stripe rust was reported in a field near Precott in the Walla Walla County, WA. Last week, a sample of wheat plants with barley yellow dwarf and crown rot from Horse Heaven Hills region (Benton Co., WA) was found to have a very tiny stripe of stripe rust pustules. Yesterday, stripe rust was reported in an August-planted ‘Tubbs 06’ field near Ritzville (Adams Co., WA). I got an e-mail that stripe rust was found on lower leaves in an early-September planted ‘ORCL 102’ field between Precott and Walla Walla. Yesterday, I was checking fields in western Whitman, Columbia, Walla Wall, Franklin, and Adams counties in eastern Washington and around Pendleton and Hermiston (Umatilla Co.) in eastern Oregon. Winter wheat ranged from early jointing (Feeks 4) to early boot (Feeks 10). I only found stripe rust on lower leaves of one volunteer plant in our stripe rust nursery (planted in late September) near Walla Walla. No stripe rust was found on any entries and spreader rows of a highly susceptible genotype. No stripe rust was found in any commercial fields checked including those around Precott and in the Horse Heaven Hills. The observations of just starting stripe rust are about normal time. The stripe rust pressure is much lower than the situation this time of last year, and even lower than that of 2010.
For wheat growers in the eastern PNW, please keep in mind that stripe rust can be different from year to year and this year is definitely different (much lower) from last year, and therefore disease management should not repeat what you did last year. You may able to save fungicide application cost this year. Real control with fungicides should be started from now. Please check your fields before spray. My general suggestion is no spray without seeing rust and spray when rust reaches to 1 to 5% prevalence (percent of plants with rust pustules). Based on current low stripe rust pressure, susceptible and moderately susceptible varieties (Table 1) may just need only one application at the flag-heading stage; and moderately resistant varieties may or not need to spray fungicides (depending upon weather conditions in May). The long-term weather forecast for May to July just issued today predicted a slightly cooler than average (just 1oF difference) for the PNW.
In California, stripe rust has been widespread. Samples collected by collaborators were from Yolo Co. and Kings Co. with severity more than 80% and prevalence up to 80%. Barley stripe rust has been reported in Davis.
Stripe Rust in the Eastern U.S.
Wheat stripe rust has been widespread in eastern U.S. (states east of the Rocky Mountains). So far, stripe rust has been reported in Arkansas, Mississippi, Texas, Louisiana, Tennessee, Kentucky, Oklahoma, Kansas, Georgia, Illinois, Indiana, Nebraska, and North Carolina. The disease will likely show up in further north states, such as Colorado, South Dakota, North Dakota, Iowa, Minnesota, Ohio, and Virginia; and cereal workers and growers should check fields for stripe rust. The current stripe rust distribution can be traced back to previous storm events (Fig. 1). The disease has caused significant damage in the south central states, especially Arkansas and Mississippi; and is causing damage further north. The disease has mostly passed the management period (before flowering stage) and is slowing down in the south-central states (Texas, Oklahoma, Arkansas, Louisiana, and Mississippi). Fungicide applications are still possible and may be needed in further north and east states. Regarding stripe rust distribution, we will like to see the same situation as in 2010. Rust damage this year appears less than 2010 in the south-central states, thanks to the warm-to-hot weather in March which made adult-plant resistance (mostly also temperature sensitive) relatively effective compared to the wet and cool weather conditions in 2010. It is too early to see damage in the central and possibly northern Great Plains and eastern states as the disease still has potential to cause damage. Fungicides should be used in fields of susceptible varieties with presence of stripe rust. Yield increase of 3 or more bushels per acre should justify application of fungicides.
So far, we have obtained virulence data from eight stripe rust samples, 4 from Arkansas, 2 from Mississippi, and 2 from Texas. All of these isolates were identified as race PSTv-37 (virulent to genes Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44, YrTr1, and YrExp2; avirulent to Yr1, Yr5, Yr10, Yr15, Yr24, Yr32, YrSP, and YrTye), except one isolate (collected from cv ‘Beretta’ from Arkansas) as PSTv-14 (virulent to genes Yr1, Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44, YrTr1, YrExp2, and YrTye; avirulent to Yr5, Yr10, Yr15, Yr24, Yr32, and YrSP). PSTv-34, which is similar to previous races PST-98 and PST-100, was the most predominant race in 2010, especially in the eastern U.S., and the second popular race in 2011. PSTv-14, one of the top five races in 2010 and 2011, was detected only in the western U.S. in both 2010 and 2011 and appeared to have been spread to the eastern states.
Fig. 1. Storms which may have caused stripe rust spread.
Thunderstorms forecasted or occurred on March 2 and March 3.
Forecast on March 19, 2012 and April 14, 2012
Table 1. Stripe rust reaction groups (R=resistant, MR=moderately resistant, MS= moderately susceptible, and S=susceptible) and predicted yield losses of major winter wheat cultivars grown in the PNW based on last year yield losses and this year prediction of stripe rust damage
|Cultivar||Stripe rust AUDPCb,c||***Yield (BU/A)**||Yield loss (%) 2011||2011 relative yield loss (%)||2012 relative yield loss (%)||Res.|