Stripe Rust Update April 29, 2015

Xianming Chen

Stripe Rust Occurring in the Palouse Region

Stripe rust was first observed as a single rusting leaf in the susceptible spreader rows in one of our winter wheat experiment field on Whitlow Farm near Pullman on April 20.  On April 28, I was checking fields in the Palouse region (Whitman County of Washington and Latah County of Idaho).  Winter wheat ranged from Feekes 5 to 7 and from poor (uneven stand) to good (quite uniform).  Spring fields ranged from Feekes 3 to planting or not planted.   No rust was found in any of commercial winter wheat fields checked.  Stripe rust was found in two (Whitlow Farm and Spillman Farm) out of our three experimental field sites around Pullman.  In both locations, seven to ten spots of stripe rust were found, mostly one rusting leaf in a spot with three or five rusting leaves at a couple of spots.  All of the spots were still just in the susceptible check rows or spreader borders.  In the AgriPro-Syngenta breeding nurseries about four miles southwest Colfax, stripe rust was found at a couple of spots.  In all of these spots, stripe rust were mostly on the bottom leaves and occasionally on top leaves (Figure 1).

The appearance of stripe rust is about two to three weeks earlier than normal for the region, and is expected based on the previous forecast.  Early application of fungicides is necessary for fields planted with susceptible or moderately susceptible varieties.

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Figure 1. Stripe rust observed in an experimental field near Colfax, Washington on April 28.

Stripe Rust in the U.S. and Canada

So far, stripe rust has been reported in 17 states in the U.S.: Oregon, Louisiana, Texas, Arkansas, Mississippi, Oklahoma, Washington, California, Montana, Arizona, Colorado, Kansas, Nebraska, Tennessee, Georgia, Utah, and Idaho.  Fungicides have been used to control the disease in many of these states.

According to Kequan Xi, stripe rust was found on April 16 in winter wheat in the Olds breeding site, about 80 km south of Lacombe, Alberta, Canada.  Also based on André Laroche, stripe rust was observed in a few winter wheat fields near Lethbridge, Alberta.  The rust on low leaves in Alberta indicates that the pathogen has overwintered there.