Stripe rust is developing in Washington and northern Idaho
Over the past two weeks since the last update on May 23, stripe rust has developed to significant levels in south-central, central and eastern Washington and northern Idaho. In Walla Walla County, winter wheat ranged from flowering to grain filling stages. Stripe rust was generally low (1 to 10% of severity and up to 30% of incidence) in commercial fields. In our experimental field near Walla Walla, stripe rust developed to 60% of severity and incidence on susceptible entries of winter wheat and just started (about 2% of both severity and incidence) on susceptible spring wheat spreader by June 7. In the Connell and Kahlotus area in Franklin County, winter wheat ranged from headed to milk stage and stripe rust (about 2-10% of severity and 1 to 20% of incidence) was found on both winter and spring wheat crops as observed on June 5. Most rust pustules had turned into black pustules (telial stage), which are no longer able to produce infectious spores for wheat crops and indicate the presence of the PSTv-11 and PSTv-14 (previously PST-127) race group. In Adams County, winter wheat crops ranged from heading to milk stage and more severe stripe rust (up to 40% of severity and 20% of incidence) were found in commercial fields along HW21 to Dusty and around Ralston, actively producing orange infectious rust spores, as observed on June 7. In the Palouse region (including Whitman County of Washington and Latah County of Idaho), winter wheat ranged from early boot to headed by June 7. Stripe rust was hard to find in most checked commercial fields on May 29 and June 7, except some fields near St John in Whitman Co. where stripe rust of 10% incidence and severity was observed (on May 29). On May 29, several stripe rust hot spots of up to 30% severity were observed in some highly susceptible entries and rust developed from bottom to top in a breeding nursery about 5 miles southwest Colfax, indicating overwintered rust inoculum. By June 5, the hot spots expended to cover some of the entry plots and severity reached 60%. This experimental field has had the most sever stripe rust observed so far in the Palouse region. In our experimental fields around Pullman, stripe rust developed up to 20% of both severity and incidence on susceptible winter wheat entries by June 7. In the same location, stripe rust was first found on a winter barley line and just started (found a couple of small rust pustules) on susceptible spreader rows of spring wheat (planted in the middle April, reached Feeks 5) on June 7. On the same day, low levels of stripe rust (5% severity and incidence) were found in a McGregor variety trial west of Dusty (Whitman Co.). Stripe rust of up to 10% of severity and incidence was found in a UI variety trail nursery near Moscow. No stripe rust was found in commercial fields around Colton, Colfax, Dusty, Palouese, and Pullman in Whitman County, and Moscow and Genesee in Latah County, except one small rust stripe was found in a field south of Moscow.
The weather conditions in the last two weeks and forecasted for the next 10 days are very favorable to stripe rust in Washington and northern Idaho. Rains and showers since May 28, especially this week, plus the low temperatures, have created ideal conditions for stripe rust infection. Therefore, stripe rust is predicted to develop more rapidly in the next three weeks than in the past three weeks. As stated in the last rust update (May 23), our general recommendation for spraying field of susceptible and moderately susceptible cultivars is still recommended. Also, please check your fields before spray. It will be better to spray when you see rust reaching 1 to 5% severity and/or incidence. Please check fungicide labels before use. When a crop has past flowering stage, most fungicides could not be used.
No leaf rust and stem rust have been found or reported on wheat in eastern Washington and northern Idaho. A barberry bush near Potlatch (Latah Co.), Idaho and a couple of bushes east of Colfax (Whitman Co.), Washington were found producing abundant aeciospores (presumably stem rust able to infect wheat and barley) on May 28. With the good moistures since, stem rust may develop to significant levels on wheat and barley in the Palouse region.
Nationally, stripe rust has been widespread this year, almost like the wide distribution in 2010. Comparing this year and 2010, stripe rust has been reported so far in all of the state with significant levels in 2010 except New York State.