Xianming Chen
The spring wheat crop, ranging from boot to flowering stage, reaches the critical time for fungicide application. Many fields of spring wheat have already sprayed with fungicides. If a field of susceptible variety was sprayed before mid May, it may need another spray if you see 5% to 10% infection of stripe rust with active rust pustules. The weather conditions forecasted for next 10 days are still favorable to stripe rust. HTAP resistance in Alpowa and Louis is working and will be continuing work. The HTAP resistance appears as various lengths of necrotic stripes with limited or without rust pustules depending upon resistance level. Some Alpowa fields can be ugly looking and have some yield losses (estimated from 5 to 20% depending upon locations of various moistures), but will have much less damages than susceptible varieties such as Zak (yield losses will be over 40% without control). Therefore, Alpowa fields may be sprayed or not sprayed depending upon your field locations and yield potentials. Use the 5 to 20% yield losses to guide your decision making. The spring varieties that were susceptible last year also are susceptible this year. A major change of spring wheat is that several hard red or hard white varieties such as WPB 926, Hank, Jefferson, Lolo, Tara, and Nike which were highly resistant up to the last year, had more susceptible plants this year, which may need to spray with fungicides. Otis got more infection this year. These varieties appeared to be mix of plants with resistant and susceptible reactions. Please check fields of these varieties for spray if necessary, and also keep in mind that these cultivars may not have HTAP resistance.
As the growth season is progressing, stripe rust on the winter wheat crop is slowing down. The winter crop has generally passed the flowering stage and fungicides can not be used. The following observations have caught our attention and should be considered to choose varieties for future stripe rust management. 1) Hard red winter wheat varieties as a group were susceptible to stripe rust. Varieties like Hatton, Buchanan, and Moreland are highly susceptible. Moderately resistant to moderately susceptible varieties like Finley and Boundary have had expected reactions, but reached very high severities that warrant the use of fungicides in some locations, due to the early stripe rust development, heavy inoculum load, and extremely favorable weather conditions. Moreland was resistant two years ago, but became susceptible last year to new races. 2) Soft white winter varieties as a group had good levels of resistance. Madsen, Stephens, and Rod still held the good levels of resistance although necrotic stripes (resistant reactions) were commonly found on these varieties. One of the big changes of soft white winter wheat was Eltan. This year, Eltan got more stripe rust infection than we ever saw before. This was due that the seedling resistance in Eltan was overcome by new races and the high-temperature adult-plant (HTAP) resistance was not fully expressed under the cool and wet weather conditions and the heavy rust inoculum load. The HTAP resistance in Eltan should provide adequate control under a normal weather and rust conditions. 3). Many club wheat varieties, such as Bruehl, Chuckar, and Coda were still resistant.
A big change was Hiller. The seedling resistance in Hiller was no longer effective due to appearance of new races. However, Hiller still has a useful level of HTAP resistance that may be adequate in years when stripe rust is not so severe. Old club wheat varieties Moro, Paha, and Tres were susceptible this year. Stripe rust races virulent on these varieties were predominant in 1970s and/or 1980s, but decreasing in 1990s and almost disappeared from 2000 to 2002. New races that are virulent on these varieties started showing up in 2003 or 2004 had the combinations of virulences on one or two of these varieties and PST-100 in the new group of races we have talked since 2000. These races have overcome the seedling resistance in some club wheat and possibly in some common winter and spring wheat. 4). Some varieties such as Tubbs, Dune, and Brundage 96 showed various reactions to stripe rust due to the mix genetics of the varieties. These varieties have been reselected to eliminate susceptible plants. 5) Widely spread physiological leaf spot caused confusions with stripe rust infection. Because stripe rust (using Quilt, Tilt, Quadris, Headline, and Stratego) and physiological leaf spot (using potassium chloride) are controlled by different chemicals, they should be clearly distinguished.
Barley stripe rust is developing quickly in fields of susceptible varieties. A field of hooded barley variety just north of Colton, WA had almost 100% of plants infected and the severities were up to 80%. 100% stripe rust also were observed in breeding nurseries at Tammany, ID (southeast of the Lewiston area). Fields of susceptible barley varieties such as Morex, Harrington, Steptoes, and many others should be checked, and spray if the rust reaches 5-10% of severity. Baronesse and Bob have good levels of HTAP resistance and should be fine without spray.
If you have any questions, please feel free to contact me (Phone: 509-335-8086; e-mail: xianming@mail.wsu.edu)