August 19, 2010
Wheat stem rust occurred again in the Palouse region (Whitman Co. of Washington and Latah Co. of Idaho) this year. As reported previously, the barberry bushels near Potlatch, Idaho (Latah Co.) were severely infected. We were able to recover stem rust from barberry leaves collected in the last week of July. The spring wheat field surrounding the barberry bushels had no stem rust except for few volunteering plants from the winter wheat crop last year. The winter wheat field, which is beyond the spring wheat crop and further away from the bushels got infected at a severity level much less than that of last year. The spring wheat crop obviously has good resistance and the low level of stem rust in the winter field might be due to the facts that the field is further away from the bushes and that the field was sprayed with fungicide to control stripe rust.
With the help of McGregor people, Tim Murray and I yesterday looked at two winter wheat fields grown with ‘AP 700CL’ and ‘ORCF 102’ between Palouse and Colfax, which had significant stem rust. Many big hotspots (up to 50 meters in diameter) occurred in these fields. Plants in the centers of the hotspots had more than 80% of severity. Rough estimates of yield losses for the entire fields in average were about 3 to 5%. The ORCF 102 field is within three mile of a couple of barberry bushes along the Palouse River we have checked several times this year. These bushels got stem rust infection, but at a very low level. The significant level of stem rust in the ORCF 102 field and some nearby fields indicate that additional barberry bushes may exit nearby.
Dr. Robert Allan found stem rust on ‘Brevor Rht8 NIL’ in his breeding field near Pullman, WA (Whitman Co.). This morning, we also found stem rust on ‘McNair’ and a couple of other lines in our spring wheat nurseries near Pullman. Rust was mainly on late and still green tillers.
Compared to the last year, stem rust was more significant in the Palouse region, especially Whitman County this year.
While effort is taking to remove the known barberry bushes in the region, there may be more bushes there. Although, unlike stripe rust, stem rust has less chance to cause widespread epidemic in eastern Washington and northern Idaho, significant damage can occur in a localized manner, which may result in significant profit loss for individual growers. Therefore, it is better to take stem rust into consideration for growing wheat crops. Fungicide application for controlling stem rust is not as effective as for controlling stripe rust in this region as stem rust occurs in very late stage of growth (usually after flowering stage). Avoiding very late crop helps to reduce the risk. However, the most effective approach is to grow resistant varieties or avoid most susceptible varieties. Fortunately, some of the PNW wheat varieties are resistant to the regional population (but not Ug99) of stem rust. I attach preliminary data of our evaluation for stem rust reactions of wheat entries in the 2009 Variety Trial and Regional Uniform Nurseries of both winter and spring wheat for the local growers to consider. After you considering yield, quality, stripe rust resistance, and adaptation, you should choose variety with resistant or moderately resistant reactions, at least avoiding ones susceptible to stem rust, if possible. Please keep in mind that the test was conducted with only one isolate from a bulk collection made from the wheat field near the barberry bushes in 2009. Some resistant or moderately resistant varieties could be susceptible to other isolates we have not tested. At least, the resistant and moderately resistant varieties should have less chance to be damaged than the susceptible and moderately susceptible ones.