Stripe Rust
Update:
Stripe rust has developed slower this year than in 2011, with levels lower than
2011 or 2010. There have been a few reports of it in Umatilla and Walla Walla
Counties, but it is not widespread and is about normal for the stage of
development for wheat in the area. In eastern Washington and northeastern
Oregon, stripe rust has started showing up, but still remained hard to
find. Dr. Xianming Chen, USDA ARS, Pullman, was checking fields in western
Whitman, Columbia, Walla Wall, Franklin, and Adams counties in eastern
Washington and around Pendleton and Hermiston (Umatilla Co.) in eastern Oregon
this week. He notes that winter wheat ranged from early jointing (Feeks
4) to early boot (Feeks 10). He only found stripe rust on lower leaves of
one volunteer plant in our stripe rust nursery (planted in late September) near
Walla Walla. No stripe rust was found on any entries and spreader rows of
a highly susceptible genotype. No stripe rust was found in any commercial
fields checked including those around Prescott and in the Horse Heaven
Hills.
The
following graph, provided by Dr. Mike Flowers, OSU, shows the generation time
which is the time from infection to
visible stripe rust in Hermiston area.
As the temperatures increase, the generation time decreases. As you can tell from the graphs, the
generation time for stripe rust is currently running around 15-20 days,
depending on location.
Figure:
Stripe Rust Generation, April 24, 2012
Please
check your fields before spraying. Our general recommendation is no spray
without seeing rust and spray when rust reaches to 1 to 5% prevalence (percent
of plants with rust pustules). Based on current low stripe rust
pressure, susceptible and moderately susceptible varieties may just need only
one application at the flag-heading stage; and moderately resistant varieties
may or not need to spray fungicides (depending upon weather
conditions in May) according to Dr. Chen. The long-term weather forecast
for May to July just issued today predicted a slightly cooler than average
(just 1oF difference) for the PNW.
