By Xianming Chen
Last week, we were checking wheat fields in Whitman County of Washington and Latah County of Idaho. Winter wheat ranged from boot (Feekes 10) to flowered (Feekes 10.53). Crops in most fields were in excellent condition. Stripe rust was found in few commercial winter wheat fields in very low incidence (less than <0.1 percent). Most of the infections occurred on top leaves, indicating the infection occurred in this spring. We only found one plant infected last fall between Malden and Pine City in Whitman County. In contrast, stripe rust has developed fast in our experimental fields near Pullman, Wash., since the last report in on May 8. Stripe rust reached to 100 percent incidence and 30-80 percent severity on susceptible varieties.
Spring wheat ranged from late tillering (Feekes 3) to heading stage (Feekes 10.1). Stripe rust just started appearing on susceptible spring wheat varieties next to heavily rusted winter wheat plots in our experimental fields near Pullman. No rust was found in any of the commercial spring wheat fields. Also, no rust was found in the spring barley fields checked in both counties.
Stripe rust was easily found on goat grasses near or in rust-free winter wheat fields in both counties. At some spots, goat grass plants were heavily infected by stripe rust. Stripe rust on goat grass is usually wheat stripe rust and sometimes barley stripe rust. If stripe rust is only on goat grass or other grasses in or near a wheat field and wheat plants do not have rust, the rust will not affect the wheat crop because of its resistance to the particular race or races on the grass.
Severe physiological leaf spot was found in some winter wheat fields, which is caused by chloride deficiency and other factors, but not by fungal pathogens. Fungicide application does not reduce this problem.
Because stripe rust pressure is still low, for winter wheat crops before flowering (Feekes 10.5), fungicides are not recommended for the crops of resistant and moderate resistant varieties (ratings 1-4 in the Seed Buyer’s Guide), unless active rust pustules are easily found in the fields. For fields grown with susceptible or moderately susceptible winter wheat varieties (ratings 5-9), fungicide may be applied if active rust can be easily found and the crop has not passed the flowering stage. For spring wheat, fungicide is recommended at the time of herbicide application only for fields grown with susceptible and moderately susceptible varieties (ratings 5 to 9). Fungicide application is not recommended for spring barley, unless active rust can be found in the field.
Stripe rust in other states
So far, stripe rust has been reported in 15 states (Arkansas, Texas, Oregon, Washington, Mississippi, Georgia, Tennessee, Oklahoma, Louisiana, California, Kentucky, Kansas, Illinois, North Carolina and Virginia). Compared to this time of the last year, stripe rust is at relatively localized and at low levels. Depending upon the region and crop stage, stripe rust still has potential to cause localized damage in northern states.