Stripe Rust Update 4/4/12

April 4, 2012

Xianming Chen
Stripe rust found in eastern Washington and Management Recommendation

Yesterday (April 3) was the second nice spring day in much of the eastern Washington and the weather was back to winter late last night. We were checking wheat fields in Whitman, Garfield, Columbia, Walla Walla, Benton, Franklin, and Adams counties in Washington, mostly south of Highway 26. Spring wheat has been planted in some fields of western Whitman Co. and other counties. Winter wheat, ranging from Feekes 2 to 6, has not grown much since early March, but become actively growing. No stripe rust was found in any commercial wheat fields checked and also our experimental field near Walla Walla, except in experimental fields at Central Ferry along the Snake River in Garfield Co. On the Central Ferry farm, three stripe rust leaves producing spores were found in the susceptible border spreader rows in a breeding nursery of winter wheat and no rust was found on the breeding lines. The wheat plants reached Feekes 6 and the rust leaves were at the low canopy, indicating that stripe rust has overwintered. In another herbicide experimental field on the same farm (cultivar unknown), two stripe rust leaves were found. Regarding stripe rust incidence or prevalence, the percentage of sporulating (producing spores) plants on this farm was less than 0.001%. Therefore, the stripe rust pressure in eastern Washington and likely eastern Pacific Northwest is much lower than this time of the last year.

Based on the low rust pressure, fungicides are not needed when herbicides are applied in winter wheat fields from now to about four weeks. For regions where herbicides are applied about four weeks from now, consider using fungicides with herbicides only when you found stripe rust in your field or clearly know stripe rust actively increasing in the surrounding areas. It is likely that fungicide may not be needed until flag leaf stage depending upon the weather conditions in May and June. Our next report will be in the last week of April or the first week of May.

Please note that crown rot is quite common in early planted winter wheat fields in the Horse Heaven Hills region of the Benton Co. and the dry areas along Highway 26 in Franklin and Adams Co. Severely infected plants are much shorter and dying, and lightly infected plants have low leaves yellowing. Do not mistreat these plants as infected by stripe rust. Management methods for crown rot and stripe rust are different, except that late planting in the fall helps in reducing both diseases.

Stripe rust in western Washington

Our crew went to Mount Vernon on March 29 and 30 in northwestern Washington. Winter wheat reached Feeks 7. As usual, wheat stripe rust developed to 100% prevalence and 60% severity on susceptible lines. As a standard approach, fungicide application is always needed for susceptible cultivars in this region.

Stripe rust in other states

In addition to Washington, wheat stripe rust has been reported so far in Arkansas, Mississippi, California, Texas, Louisiana, Tennessee, Kentucky, Oklahoma, and Kansas; and caused significant damage in some of the states. Growers in Arkansas and some other states have actively sprayed fungicides to control stripe rust and other diseases.

Yr17” resistance

The first sample from Arkansas was identified as race PSTv-37, which is virulent to resistance genes Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44, YrTr1, and YrExp2 and avirulent on Yr1, Yr5, Yr10, Yr15, Yr24, Yr32, YrSP, and YrTye. Please note that the Yr17 resistance is a complex issue. Based on our greenhouse and field data of Yr17 “single-gene” line and cultivars with Yr17, we hypothesized that this race-specific all-stage (seedling) resistance gene is linked to a gene(s) for high-temperature, adult-plant resistance. Therefore, “Yr17” appeared highly susceptible in the south-central states in 2010 when weather was cool and wet and stripe rust pressure was high; and appeared to be resistance this year when temperatures have been relatively high and rust pressure has been relatively low in the region compared to 2010.