Stripe
Rust Forecast and Update
March
5, 2012
Xianming
Chen
Field survey
On
March 1, I was checking wheat fields in Whitman, Columbia, Walla Walla, Benton,
and Franklin counties in Washington, mostly south of Highway 26. Plants
ranged from two-leaf stage to early jointing (Feekes 1-5), depending upon
planting time and region. In most wheat
fields, plants were still in winter dormancy and did not grown much compared to
growth stages in early November, but became uniform especially in late planted
fields. No rust was found in any of the checked
fields. There was no obvious winter
injury or other diseases.
Prediction and management
suggestion
Using
a series of forecast models based on various weather parameters from December
to February (Sharma-Poudyal and Chen, Phytopathology 101:544-554, 2011), the
new prediction of potential yield loss
caused by stripe rust on susceptible winter wheat varieties is 35±5%, dropping
from the 47% forecasted based on only the December weather.
This level is within a moderate epidemic category. The prediction is based on historical yield
loss and weather data of the Palouse region and is applicable for most wheat
growing regions in the Pacific Northwest, except western Washington, western
Oregon, and southern Idaho as these regions have very different weather
patterns.
Stripe Rust in 2011. |
With the moderate level of
damage potential, susceptible and moderately susceptible varieties may need to
be sprayed with fungicide (possibly just once) and resistant and moderately
resistant varieties may not need spray.
Please keep in mind that the current prediction can be realized only if
the weather conditions from now throughout the remaining growing season are
normal (past long-term averages). If May
and June are unusually cool and wet, just like in 2010, stripe rust would be
severer than the current prediction. On
the other hand, if the weather conditions from April to June are drier and from
May to June hotter than normal, stripe rust would be lower than the current
prediction.
Nevertheless, based on the current prediction
and field observations, stripe rust will definitely not be as severe as 2011
(but still have possibilities to be as severe as in 2010), applications of
fungicides may not be necessary until you see stripe rust (5-10% incidence) in
your fields.
Checking fields should be started from later
March in eastern Oregon and southern-central Washington (Horse Heaven Hills,
Connell areas, and Walla Walla) and from middle April in areas further north
and east in Washington and Idaho. In
western Washington, stripe rust should be visible as always in this time of the
year. Application of fungicides together
with herbicides in fields grown with susceptible and moderately susceptible
varieties should be a standard procedure for maximizing profit every year in western
Washington.
Current stripe rust situations in
other states
Stripe
rust was first reported in Arkansas on January 27, in Mississippi on January
30, in California in the last week of February, and in Texas on March 1. Stripe rust has been developing and spreading
quickly in Arkansas and Mississippi. The recent storms and tornadoes would have
spread stripe rust spores to infect wheat fields in states further north and
east.
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