First Forecast of Stripe Rust for 2015 and 2014 Yield Losses
Forecast for 2015
The current forecast is that highly susceptible winter wheat varieties would have 38% yield loss, in the high end of moderate epidemic range (20-40% yield loss). Based on this forecast, currently grown varieties would have 0 to 20% yield loss, depending upon the level of susceptibility. This forecast is based on the November and December temperatures. In early March, we will make another forecast based on the weather conditions of the entire winter season, which is generally more accurate than the early forecast.
In the last week of November, we checked winter wheat fields in Whitman, Adams, Lincoln, and Grant counties in the state of Washington. No rust was observed. Winter injure, caused by the unusually cold spell in the second week of November, was evident in many wheat fields.
In contrast to Washington, stripe rust was reported in many locations in Montana and Wyoming in October and November.
Stripe rust yield losses of wheat varieties in 2014
Under natural conditions, stripe rust had the lowest level in 2014 during the past 15 years in the PNW, as forecasted in March. Commercial fields generally did not need fungicide application. The low level of stripe rust was due to the cold winter and also the hot and dry summer.
Because of the potentially low stripe rust, we inoculated our experimental fields near Pullman in the early spring. Differences in non-sprayed and fungicide sprayed plots of winter wheat and spring wheat varieties are shown in Table 1 and Table 2, respectively.
Of the 24 winter wheat varieties including susceptible check ‘PS 279’ tested, 12 varieties had significant differences in stripe rust, 9 varieties had significant differences in test weight, and 5 varieties had significant differences in yield. Stripe rust caused 56% yield loss on the susceptible check (PS 279) and up to 23% yield losses on commercial varieties. Under such severe stripe rust epidemic (40-60% yield loss on susceptible varieties), five commercial varieties (Eltan, Xerpha, Tubbs 06, ORCL 102, and ARS-Amber) were rated great than 1, in addition to the susceptible check, and they needed to spray with fungicides. The remaining 18 commercial varieties were rated 1, and no fungicide application was needed.
Of the 16 spring wheat varieties including susceptible check ‘AvS’ tested, all varieties, except ‘Expresso’, had significant differences in stripe rust, but only 5 varieties had significant differences in test weight and 8 varieties had significant differences in yield. Stripe rust caused 38% yield loss on the susceptible check (AvS) and up to 22% yield losses on commercial varieties. Seven commercial varieties (Nick, WB Fuzion, WB-1035CL+, SY605CL, Babe, Solano, and Jefferson) were rated 2 (>1), in addition to the susceptible check, and they needed fungicide application. The remaining eight commercial varieties (Diva, Whit, Cabernet, BR-7030, Expresso, Buck Pronto, Kelse, and Louse) were rated 1, and no fungicide application was needed.
The data can be used to select stripe rust resistant varieties to plant and to determine if fungicide application is needed for a variety based on the relative yield loss and potential epidemic level. The current forecasted epidemic level (38% yield loss on susceptible varieties) for 2015 is below the 2014 damage level (56%) in artificially inoculated experimental field.
Table 1. Differences in stripe rust severity (as rAUDPC), test weight, and yield in non-sprayed (check) and fungicide sprayed plots of winter wheat varieties tested under artificial inoculation near Pullman, WA in 2014
Table 2. Differences in stripe rust severity (as rAUDPC), test weight, and yield in non-sprayed (check) and fungicide sprayed plots of spring wheat varieties tested under artificial inoculation near Pullman, WA in 2014