Rust Update 8/9/13

August 9, 2013

Xianming Chen

Rusts in the PNW

Wheat stripe rust. As winter wheat crop has been harvesting and spring crop reached dough stage, the rust season is basically over. Stripe rust was active in northern California at high elevation, southern Idaho, and Montana last week. In most Pacific Northwest (PNW), the 2013 stripe rust season is interesting. Although stripe rust severity eventually reached 100% on susceptible checks in our experimental fields near Pullman (no inoculation and no irrigation), the damage was relatively high on winter wheat, but low on spring wheat. Yield loss on susceptible winter wheat is estimated between 40 and 50%, comparable with 2012; and less than 10% on susceptible spring wheat, less than 2012. In 2013, stripe rust appeared earlier than 2012, but later than 2011. In commercial fields, the widely application of fungicides at herbicide timing reduced the rust inoculum. With exceptions of few fields, second application of fungicides was not necessary, and basically not used. The dry weather conditions after late April and high temperatures after the first week of July also reduced the rust damage.

Barley stripe rust

This year, barley leaf rust was generally low throughout the PNW with exceptions in western Oregon. In northwestern Washington, barley stripe rust severity was the lowest since the disease first appeared there in 1995. In other regions of the PNW, barley stripe rust incidence and severity were comparable to the last several years.

Barley leaf rust

The disease occurs in northwestern Washington and has never been observed in regions east of the Cascade Mountains in the PNW.This year, barley leaf rust was much severer than the past several years. More than 90% severity was recorded on many barley entries in our experimental nurseries at Mt. Vernon.

Wheat leaf rust

This year, wheat leaf rust was lower than the past in our experimental field at Mt. Vernon (northwestern Washington) and was not found in eastern Washington and northern Idaho.

Stem rust

This week, stem rust was eventually found in the Palouse region. Dr. Bob Allan found stem rust (up to 20% severity) on a few plants of winter wheat in his breeding field between Pullman, WA and Moscow, ID. We found one pustule in one site and 5% incidence and 20% severity only in one entry of spring wheat in another site of our experimental fields near Pullman, WA. Stem rust is much lower than the situation in 2012.

Stripe rust throughout the U.S.

Wheat stripe rust occurred throughout the U.S. with the distribution much larger than 2012 and comparable to 2010. We have received wheat stripe rust samples from 28 states. This year is marked as the first of receiving stripe rust samples from Vermont. Disease levels varied greatly from region to region. In general, stripe rust was more severe in the south-central states than northern and eastern states.

Barley stripe rust occurred in Arizona, California, Oregon, Idaho, and Washington. In general, the disease was low, but comparable to the past several years.