South Perth, Western Australia
September 2, 2004
 With
the onset of spring, cereal growers throughout the wheatbelt are
being urged to regularly check their crops for signs of stripe
rust (photo).
The
Department of Agriculture, Western Australia has reported a
rapid increase in finds of stripe rust, indicating the disease
is moving quickly from its eastern and south-eastern base to
central and northern areas.
Department plant pathologist Rob Loughman said
despite proactive control in eastern wheatbelt areas, where
early infections were first detected in late July, stripe rust
had ‘jumped the fence’.
Dr Loughman said stripe rust could now be
detected at initial levels in much of the central wheatbelt as
far west as York and Northam, and north to Miling, Coorow and
possibly Three Springs.
“A succession of windy, cool and wet conditions
in the last few weeks has provided opportunity for the disease
to spread to western areas of the wheatbelt and establish in
various areas,” Dr Loughman said.
“Growers in all areas need to scout their
susceptible wheat crops to look for early signs of stripe rust.
Signs include scattered bright yellow-orange striped or specked
spore masses on leaves in areas of up to 10m of intense
infection known as hot spots.
“Rusts produce brightly coloured spores that can
be rubbed on to your fingers. Spores are released into the air
and can move hundreds of kilometres on wind currents.”
Dr Loughman said walking through the earliest
sown or most susceptible crops was critical to early detection
of the disease.
“Stripe rust can reduce yields by more than half,
and uncontrolled infections or delayed control will also
threaten other nearby wheat crops,” he said.
Dr Loughman said that many crops were at or near
flag leaf emergence, which was a good stage to control leaf
diseases in wheat. However, the most important factor was
whether stripe rust had occurred or was likely to occur in a
crop.
“Where stripe rust is detected in crops with
resistance ratings of 5 or less, it should be controlled as soon
as possible with cereal fungicide spray, including crops yet to
reach the flag leaf emergence stage,” he said.
“If after careful inspection stripe rust is not
detected, but the disease is nearby, growers can delay spraying
until full flag emergence to provide optimal protection and
duration of control.”
A range of cereal fungicides can be used to
control stripe rust. High rates of application should be used
in situations where the disease has established on a high
proportion of plants at the time of spraying or where the
variety was highly susceptible.
In some situations, it may be necessary to spray
susceptible crops more than once and fungicide treated crops
should be re-inspected three weeks after treatment for signs of
new stripe rust activity.
Dr Loughman said partial resistance in some
varieties expressed at late stem elongation, coinciding with
flag (or top leaf) emergence.
“These varieties with a resistance rating of 5 or
6 cope better with the disease during grain fill compared to
susceptible varieties with a rating of 2 - 4 and are less likely
to require follow-up fungicide spray,” he said.
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