Stripe Rust Update, April 13, 2016

Xianming Chen

Stripe Rust in the Pacific Northwest

On April 7, I was checking wheat fields in Whitman, Garfield, Walla Walla, and Franklin counties of Washington and Umatilla County of Oregon.  Winter wheat ranged from Feekes 4 to 8, and generally in good conditions.   Stripe rust was found in several fields of Garfield, Franklin, and Walla Walla counties in low prevalence and severity.

In our experimental field near Walla Walla, stripe rust had developed from early March to early April, which allowed taking an early note.  The susceptible check (PS 279) had 100% prevalence and 15-30% severity.  Among the commercially grown varieties in the Variety Trial Nursery, SY Clearstone CL2, AP 503 CL2, Finley, Esperia, Mandala, WB-Junction, SY 107, ARS-Crescent, Xerpha, ORCF-103, WB 528, and Rosalyn had susceptible reaction (IT 8) with severity of 2-20%.  No rust or resistant reaction (IT 2-3) was recorded for LCS Colonia, LCS Jet, WB-Arrowhead, HE 181/3, Bauermeister, Earl, Farnum, LCS-Azimut, NSA 10-2196, Norwest 553, WB-Rimrock, LCS Aymeric, LCS Evina, WB 4059, Rebaldi, LOR-092, LOR-913, WB 1604, LOR-334, Mary, ORCF-102, Legion, UI Castle CL+, UI Magic CL+, UI Palouse CL+, UI-WSU Huffman, Madsen, Curiosity CL+, Jasper, KXB-01, MelaCL+, Puma, WB 1843, Coda, Bruehl, Eltan, Masami, Otto, WB 523, Bobtail, LOR-833, Skiles, AP700 CL, SY Ovation, ARS-Selbu,  and Cara.  Varieties with intermediate reaction (IT 5) included Keldin, Whetstone, WB 1529, LCS-Artdeco, and KWS 034.  As these data are only from one location and in the early season, they should be used in combination with previous data for making decisions for applying fungicides in a field of a particular variety.

In a field planted with wheat variety Whetstone near Pendleton (Umatilla County, OR), every plant was infected with severity of 20-40% (Figure 1).  Plants had necrotic stripes and stripe rust pustules, indicating that high-temperature, adult-plant (HTAP) resistance had started working.  This is the most uniformly and heavily infected field observed so far in the eastern Pacific Northwest.

At the Hermiston station (Umatilla County, OR), stripe rust was easily found in various nurseries.  The susceptible varieties in our stripe rust monitoring nurseries had the highest prevalence and severity with the susceptible check (PS 279) reaching 100% prevalence and up to 60% severity (Figure 2).  Spring wheat also got stripe rust.

On April 6, our crew found stripe rust in our nursery at Lind (Adams County, WA), where we did not found stripe rust in early March, but found stripe rust in commercial fields in surrounding areas in early and late March.

On April 12, I was checking wheat fields in the Palouse region (Whitman County of Washington and Latah County of Idaho).  Winter wheat ranged from Feekes 3 to 6.  Stripe rust just started developing.  I found stripe rust on the susceptible check at very low prevalence in our nursery on the Spillman Farm (Figure 3), but did not found stripe rust in two other locations planted later around Pullman.  No stripe rust was found on the UI Farm outside of Moscow.  Two leaves with small stripe rust patches just starting sporulation were found in a commercial field at Viola (Latah County, ID) about 15 miles north of Moscow.  One leaf with stripe rust was found in a commercial wheat field near Palouse (Whitman County, WA) (Figure 4).  The appearance of stripe rust in the Palouse region is similar as the last year, but about one month earlier than normal.

On April 4, Juliet Marshall reported stripe rust found in two fields, both planted with Brundage, in southeastern Idaho.

So far, stripe rust is widespread in the Pacific Northwest.  Weather conditions will continue favoring stripe rust infection and development for next several weeks.  The general recommendations are the same as those made in the previous stripe rust updates.  Early fungicide application (at the herbicide application time) is necessary for fields planted with susceptible and moderately susceptible varieties.  For resistant and moderately resistant varieties, fungicide application may not be needed unless active stripe rust is found in the fields.  Second application of fungicides may be needed three to four weeks after the first application when active stripe rust pustules starts appearing.  For spring wheat, select resistant varieties to plant, if not planted yet; and check fields for stripe rust three weeks after planting.  If active stripe rust pustules start appearing, consider using fungicides.

Stripe Rust in the Country

This is another year of severe stripe rust epidemic in the country.  So far, stripe rust has been reported in 16 states: Texas, Oregon, Louisiana, Arkansas, Oklahoma, Washington, Colorado, Kansas, Mississippi, California, Virginia, Montana, South Dakota, Kentucky, Indiana, and Tennessee.

 

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Figure 1.  Stripe rust in a commercial wheat field near Pendleton, OR, April 7, 2016

 

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Figure 2.  Stripe rust in a rust monitoring nursery near Hermiston, OR, April 7, 2016

 

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Figure 3. Stripe rust found in a rust nursery near Pullman WA on April 12, 2016

 

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Figure 4. Stripe rust found in in a commercial wheat field near Palouse, WA on April 12, 2016