Stripe Rust Alert

May 18, 2005

Xianming Chen

Wheat stripe rust is almost everywhere in the Pacific Northwest and barley stripe rust starts showing up in eastern Washington.

I was checking fields for rust yesterday mainly in Whitman County. Our crew was taking rust notes at Walla Walla. John Burns, Kim Kidwell, Gary Shelton, Steve Anderson, and many others were all checking for rust situations recently.

Wheat stripe rust is widespread, almost everywhere we have looked. In Walla Walla, stripe rust has already developed up to 100% severity on susceptible entries in our winter wheat nurseries, and 40% in our spring wheat nurseries. In our nurseries and breeders’ nurseries around Pullman with natural infection, stripe rust has developed up to 20% severity on susceptible entries.

In commercial fields, winter wheat crop is generally in good shape and does not need to be sprayed, except for a few fields where stripe rust has developed to 5 to 10% severity, which need to be sprayed. Stripe rust is very common in spring wheat fields, mostly less than 2% severity and on the first leaves from the ground surface. The earlier the field was planted, the more leaves that are showing rust.

Barley stripe rust now can be easily seen in our experimental fields under the natural infection, about 2% severity and 1% incidence. Stripe rust was found in a barley field near Endicott in Whitman County, about 1% severity. This was the earliest detection of barley stripe rust in eastern Washington for the last five years.

The recent wet and cool weather conditions have been ideal for stripe rust infection. The forecasted little bit warmer weather for next week and later will make stripe rust symptoms develop faster. Therefore, we will likely see a rust exploration in many spring wheat fields and some winter wheat fields. The next couple of weeks will be very critical for stripe rust control. Please consider the following suggestions:

  • Know your varieties’ reactions to stripe rust. You can get the information mostly from the seedbuyer’s guide and based on your experience in the last two years. Currently grown varieties can be group into the following 3 groups:
    1. Varieties susceptible last year will be susceptible this year. For example, winter wheat varieties Hatton, Buchanan, Columbia 1, WPB 470, and Moreland and spring wheat varieties Edwall, Zak, Calowa, Scarlet, and Macon. Varieties in this group doe not have resistance against the current races of the stripe rust pathogen.
    2. The varieties previously rated moderately resistant or moderately susceptible, which may not need a fungicide spray in a normal year, should be watched closely and use fungicide when necessary. For example, winter wheat varieties such as Finley, Braundage 96, Boundary, Tubbs, and Edwin and spring wheat cultivars Alpowa, Express, Wawawai, and Penowawa, and Eden should be sprayed. Varieties in this group have from low to moderate levels of high-temperature, adult-plant (HTAP) resistance and/or contain some percentage of susceptible plants.
    3. Varieties resistant last year should be generally resistant this year. The major soft white varieties such as Madsen, Eltan, Stephens, Daws, Hill 81, and Rod; club wheat varieties Bruehl, Chukar, Rely, and Hiller; and spring wheat varieties such as Tara, Hollis, Jefferson, Hank, IDO377s, and Jerome should be resistant. Varieties in this group have adequate level of resistance (high level of HTAP resistance, effective all-stage (also called seedling) resistance, and/or combinations) and do not need spray. However, fields of these cultivars should be checked because new races attacking some of these cultivars are possible.

    Check fields closely and frequently, especially look at low leaves. Rust in lower leaves will move up quickly. If you plant spring wheat about a month ago, you should be able to see stripe rust now, unless varieties are resistant, such as some of those in the C group.

  • Fungicides should be used on time. If a spray is too early, it will likely leave the late growing stage unprotected. If a spray too late, rust may have already done some level of damage, which reduces profit. A common mistake is spaying too late to have the maximum protection. If a field has 5 to 10% stripe rust severity or incidence, it should be sprayed, unless you know 90-95% of plants in the single variety are resistant.
  • How many times a field should be sprayed? For most rain-fed fields, one spray should be adequate for winter crops. For spring wheat, varieties in the A group should be sprayed from now to before the stem elongation stage, and they may need a second spray before the flowering. Spring varieties of group B need an early spray this year because HTAP resistance will likely not start working until the stem elongation or boot stage when weather is warm enough. Even spring wheat varieties with a high level of HTAP resistance, such as Otis and Louis, they should be sprayed this year because they are susceptible to some of the current races in the seedling stage. Alpowa is susceptible in the seedling stage to most races. Therefore, it is expected to see rust in these spring wheat fields now. For this group of varieties, one early spray should control the rust.

If you have any questions, please contact me (509-335-8086, xianming@mail.wsu.edu) or David Wood (509-335-4789, 509-335-8715, dawood@mail.wsu.edu).