Stripe Rust Update, May 23, 2012
excerpts from Dr. Xianming Chen's Report
Wheat Stripe Rust in eastern Washington and eastern Oregon
Yesterday, I was checking wheat fields in Whitman, Columbia, Walla Walla, Benton, Franklin, and Adams counties of Washington and the Pendleton and Hermiston areas in Umatilla county of Oregon. Winter wheat ranged from late jointing (Feekes 9) to flowering (Feekes 10.5) with most fields at boot (Feeks 10) to heading (Feeks 10.2). Spring wheat ranged from not emerged to early jointing stage (Feekes 4). In Walla Walla Co., stripe rust was found about four out of ten fields. However, the disease developed to 40% severity in susceptible spreader rows and some entries in our stripe rust monitoring nurseries near Walla Walla, where stripe rust was found to be just started a month ago. In Umatilla Co., stripe rust was found in two fields near Milton and one field near Pendleton and was not found in about other four or five fields checked. Very low levels of stripe rust was found in fields of Pendleton and Hermiston stations. Overall, the incidences (less than 1% to 5%) and severity (1 to 10%) of stripe rust were low. Most infected leaves are upper leaves with just a single stripe, and only one hotspot of 1 foot in diameter with infection from the bottom to the top was found in a field with plants at flowering stage north of Walla Walla, indicating overwintering.
Physiological leaf spot (PLS) was a common problem in winter wheat fields in Columbia, Walla Walla, and Umatilla counties. Crown rot was severe in Horse Heaven Hills. Barley yellow dwarf (BYD) was common in early planted fields. Some fields had herbicide damage. These problems caused spots (PLS), yellowing or dead leaves (crown rot, BYD, herbicide damage) in patches or stripes in fields, which can be confused with stripe rust in distance. Please make sure to distinguish them from stripe rust as fungicides controlling stripe rust have no effect on these problems.
Weather Conditions Related to Stripe Rust
The current stripe rust pressure is relatively low, compared to the same time of both 2010 and 2011, but will increase quickly during the next two to three weeks based on spore availability and weather conditions in the last three weeks and forecasted for the next 10 days. The average temperature in May so far has been and is predicted for the entire May to be lower than normal (more favorable for infection and little bit less favorable for producing spores), but the precipitation has been and is predicted to be lower than normal in May (less favorable for infection). However, the widespread rains and showers this week should increase stripe rust infection. The low temperatures this week and forecasted for next week are not high enough for high-temperature adult-plant (HTAP) resistance to work at its best.
Recommendation for Control of Stripe Rust
Winter wheat. As winter wheat in most fields are approaching flowering stage, from now to next couple of weeks will be critical for fungicide application. The previous general recommendation remains the same for wheat cultivars in different reaction categories. The following winter wheat cultivar in the susceptible or moderately susceptible categories may need fungicide spray:
- AgriPro Paladin,
- AP Legacy,
- Tubbs 06,
- UICF Brundage (CLEARFIELD®),
- Mary (OR2040726), and
- Norwest 553,
- Chukar, and
- Finley (used to be susceptible, but was resistant in the last two years due to race changes, better to spray this year),
- UICF Grace,
- UI Silver,
- AP700 CL (CLEARFIELD®),
- ARS-Amber (ARS960277L),
- Brundage 96,
- ORCF-102 (CLEARFIELD®),
- ORCF-103 (CLEARFIELD®),
- ARS-Chrystal, and
Spring wheat. Early planted spring wheat is approaching the stage for herbicide application. For susceptible and moderately susceptible cultivars (Nick, Hank, Tara 2002, Macon, Otis, Alpowa, Babe, Bullseye, Hollis, Jefferson, and Westbred 926), it may be better to spray with fungicide together with herbicide. For resistant and moderately resistant cultivars (JD, Clear White, Diva, Louise, Wakanz, Whit, Eden, Buck Pronto, Kelse, Scarlet), it may be unnecessary to spray with fungicides.