Xianming Chen
Eastern PNW
On April 23, we were checking wheat fields in Whitman, Garfield, Columbia, Walla Wall, Benton, Franklin, Grant, Douglas, and Lincoln counties in Washington State. Winter wheat ranged from Feekes 4 to 8 and generally in good shape. We found stripe rust only on one low leaf of the susceptible check variety in our experimental field near Walla Walla. For comparison with the last year in the same location, we found more than 20 actively rust sporulating leaves on the same variety on March 7, 2013. Stripe rust is much later this year than the last year.
We checked again the Eltan field outside of Coulee City in Grant County, which was heavily infected by stripe rust in the last November. The wheat crop has recovered and grown very well. We did not find any stripe rust in the field. It appeared that the low temperatures (-2oF or -19oC recorded for Coulee City on December 8, 2013) completely eliminated the rust fungus.
Gary Shelton found stripe rust on one leaf of the susceptible check variety in a breeding nursery at Central Ferry in Garfield County about three week ago. Last Friday (April 18), he couldn’t find rust in the field. We spent more than two hours there on April 23, and could not find any rust.
Yesterday, I heard from Syngenta people that stripe rust was found in a commercial wheat field near Adams City, (Umatilla County of Oregon, just south of Walla Walla).
All these observations and reports indicate that the current stripe rust pressure is very low. Therefore, it is generally not necessary to apply fungicides now or at the herbicide application in the eastern Pacific Northwest (PNW), unless stripe rust is found in the field. Whether fungicide application is needed later or not will depend upon the rust development. For the Walla Walla area and further south in eastern Oregon, it is a good idea to check winter wheat fields from now. For other areas to the north or east, it will be good to start checking fields about three weeks from now. The general recommendation of this year is to apply fungicides only when stripe rust is found in your fields in the eastern PNW.
Western PNW
As always, stripe rust developed up to 30% severity on susceptible varieties by the first week of April in our experimental field at Mount Vernon in Skagit County in northwestern Washington. Fungicide application is always needed in early spring when susceptible cultivars are grown.
In late March, stripe rust was reported in experimental fields near Corvallis, Oregon. On April 3, Michael Flowers reported stripe rust occurring in both north and south parts of the Willamette Valley in western Oregon. Stripe rust was reported on wheat varieties Goetze, Kaseberg, Sy Ovation and Tubbs 06. Similar to northwestern Washington, stripe rust fungus survives winter very well in western Oregon almost every year. Fungicide application in the early spring is generally needed for seedling susceptible varieties.
Regarding the question about resistance gene Yr5 in new variety Kaseberg, our rust tests do not indicate that Kaseberg has Yr5. Last year, Kaseberg (OR2071628) was tested with other winter wheat entries in the WSU Variety Trial nursery at various locations in Washington State. It had infection types 2 (necrotic stripes without rust pustules), 3 (necrotic stripes with few rust pustules), to 5 (necrotic stripes with intermediate level of pustules) in the field tests. In the greenhouse tests, Kaseberg had infection type 3 to race PSTv-14, 5 to PSTv-37, and 8 (susceptible reaction) to PSTv-4, PSTv-40, and PSTv-51. In contrast, the Yr5 single gene line (used as a differential) is resistant (IT 1 or 2, no any rust pustules) in all field tests and the greenhouse race test. No any race identified so far in the US attack Yr5. The Yr5 markers developed so far are good to tell varieties without Yr5 by absence of the markers. If the markers are present, it has about 80 to 90% correctness to tell the cultivar has Yr5. We are developing more markers for Yr5 and hope to achieve 100% correctness. Currently, it is better to use the available markers together with race tests and the variety pedigree to determine presence or absence of Yr5. The pedigree of Kaseberg (WSQ910137/4/SMB/HN4//SPN/3/WTS//YMH/HYS /5/NSA 99-0792/6/WSQ910137/4/SMB/HN4//SPN/3/WTS//YMH/HYS) does not show any obvious Yr5 donor. However, Kaseberg has a good level of high-temperature adult-plant (HTAP) resistance based on last year’s field and greenhouse tests. Its HTAP resistance is likely from Stephens (SPN), Hyslop (HYS), and others in the pedigree. Because of its seedling susceptibility and adult-plant resistance, fungicide application is needed in western PNW, but may not be needed if Kaseberg is planted in eastern PNW, similar to many PNW varieties.
Stripe rust in other States
In addition to Oregon and Washington, stripe rust has been reported in Texas, Louisiana, and California, and much of the stripe rust information has been from experimental fields. In general, stripe rust has been low, and control of the disease with fungicides should be a relatively localized issue this year.