Stripe Rust Update July 3, 2014

Stripe Rust Update July 3, 2014

Xianming Chen

Stripe rust in the Palouse region

I was check fields in the Palouse region (Whitman and Spokane counties of Washington and Latah County of Idaho.  Winter wheat ranged from flowering to soft dough, spring wheat from heading to milk, and spring barley from heading to flowering.  No rust was observed in checked winter wheat fields, except one field near Palouse in Whitman County and one field (ORCL 102) near Spangle in Spokane County.  In both fields, only one or two small hot spots (less than one foot in diameter) with mixed resistant to susceptible reactions were observed on middle leaves.  In spring wheat fields, stripe rust was found in about 60% of checked fields in Whitman County and about 40% of the fields in Latah and Spokane counties.  In the fields with stripe rust observed, incidents were less than 1%, mostly just 1 to 3 single stripes (less than 1 inch) observed.  No rust was found in any of the checked barley fields.

We had adequate levels of stripe rust in our experimental fields near Pullman (Whitman County) for germplasm screening, which were inoculated.  The inoculated spring wheat plots had 100% incident and up to 100% severity.  The inoculated spring barley nurseries also had rust enough for germplasm evaluation.  According to John Moffat, the AgriPro-Syngenta breeding nursery southwest of Colfax (Whitman County), which was not inoculated, had 100% incident and 100% severity on susceptible entries by yesterday, adequate for selecting resistant material.

Other diseases in the Palouse region

No leaf or stem rust was found in any wheat field.  Significant Cephalosporium stripe was observed in many winter wheat fields in Spokane County and low levels in some winter wheat fields in Latah County.

Stripe rust in other states

So far, stripe rust has been reported in California, Oregon, Washington, Texas, Louisiana, Arkansas, Idaho, Kansas, Nebraska, Montana, Colorado, Virginia, Georgia, and Wisconsin, mostly at low levels.  By the way, significant stripe rust was reported in Alberta, Canada.

Stripe rust management recommendations

Most winter wheat fields have passed the last fungicide application time (flowering stage) and fungicide application is not needed.  For spring wheat, stripe rust will likely to increase little bit in fields of susceptible or moderately susceptible varieties in the next few days due to infections that likely occurred during and after the rains on June 17, 18, 26 and 27 in the Palouse region.  This will not be a big concern due to the current low rust pressure and effective high-temperature adult-plant resistance in most varieties.  However, if you grow susceptible varieties and your fields have long-lasting good moisture, stripe rust may be able to develop to a significant level and fungicide may be needed.  Please check your fields, if stripe rust is very easy to find (about 1-5% incident), consider applying a fungicide, otherwise, fungicide application is not needed.

Goat grass is highly susceptible to wheat stripe rust.  In some fields near Palouse grown with winter wheat, stripe rust was not found on wheat plants, but covered all leaves of grasses.  Reducing goat grasses (Aegilop spp.) and some other grasses (Hordum spp., Elymus spp., etc.) will reduce rust inoculum.

Some wheat varieties highly susceptible to stripe rust, like WB 470 and Brundage (but Brundage 96 has good resistance), should be withdrew from production.  Now, there is an IMI version of Brundage, cautions should be taken to grow this herbicide resistant variety.  For any reason, if a susceptible variety is grown, it should be prepared to timely use fungicides.