Source: Washington State University Extension

By Tim Murray, WSU Extension Plant Pathologist

new stripe rust update was released recently and, not surprisingly, stripe rust has progressed significantly in commercial winter wheat fields in Washington State since the last report severalweeks ago.

Stripe rust was found in about 16 of 80 winter wheat fields surveyed from the Horse Heaven Hills in Benton County, to Walla Walla and Whitman Counties. I was on the Columbia County Conservation District tour on Wednesday and stripe rust was found in one field of winter wheat at very low incidence.

Although rust has progressed, it’s still at a relatively low incidence in fields due to the relatively dry and cool conditions since the last report, along with fungicide applications in some fields that have held the rust in check. However, recent rainfall and warming temperatures are favorable to rust infection and development.

Growers should continue to scout their crops and make a fungicide application to susceptible and moderately susceptible winter or spring varieties when rust incidence reaches 1-5% of plants with disease. Most fungicides are effective for 3-4 weeks, so a second application may be needed on susceptible and moderately susceptible varieties that were sprayed previously.

For moderately resistant or resistant varieties, fungicide application likely will not be beneficial unless rust appears on 1 to 5% of flag leaves. Dr. Chen currently is not recommending fungicide application for spring barley because rust incidence is very low; however, continue to scout fields and apply fungicide if rust develops as described above.

In addition to stripe rust, symptoms of Cephalosporium stripe are also appearing in winter wheat. The relatively open winter with periods of frozen soil favor this disease and it was relatively easy to find in the field near Dayton this week. I’ve also had reports and samples submitted from other areas, so be on the watch. Symptoms of these two stripe diseases are not usually confused since there is no yellow-orange sporulation present on leaves with Cephalosporium stripe.

At this point, there is nothing that can be done to control Cephalosporium stripe. However, if it develops to damaging levels in a field, you should consider crop rotation (3-year is better than 2-year), delayed seeding, and selecting the most tolerant variety possible the next time winter wheat is planted in that field.