Features Agronomy Cereals
A rust of a different stripe

Stripe rust disease is somewhat common in the irrigated areas of southern Alberta,
but more cereal growers in central Alberta and southwestern Saskatchewan are
seeing their wheat, barley or triticale attacked by this yield robbing fungus.
Unlike its similar relative, leaf rust, stripe rust will infect the heads as
well as the leaves and that is when yield is affected. Of even more concern
is a newer strain of the fungus that is proving harder to control.

"For the last four or five years, we have seen a new race of stripe rust
here that suddenly appeared in the southern US in 2000," says Dr. Denis
Gaudet, a plant pathologist with Agriculture and Agri-Food Canada (AAFC) in
Lethbridge, Alberta. "Traditionally, this rust likes cool temperatures,
near 12 to 14 degrees C, but this new race germinates and infects at higher
temperatures near 18 degrees C. This permits the stripe rust fungus to develop
in the warmer conditions that prevail on the North American Great Plains rather
than in its traditional area, the inter-mountain areas of the Rockies."

Gaudet explains that the stripe rust pathogen normally originates every year
from northern Mexico or from the Pacific northwestern US and usually arrives
in the southern Canadian prairies late in the growing season. This past year,
the pathogen overwintered in southern Alberta and the early spread of the spores
on susceptible wheat varieties caused an epidemic in southern Alberta and southern
Saskatchewan. This new race is causing more and more problems every year, he
adds.

Recognizing stripe rust is the first step in determining if control is needed
or possible. Gaudet says producers should look for long striping lesions on
the leaf of the plant, which is different from leaf rust. However, both rusts
begin as small pustules on the plant at the seedling stage, but stripe rust
will increase to form stripes as the plant matures. The stress on the plant
will begin to affect yield at an earlier stage.

"The difficulty growers might have in identifying stripe rust is that
both types of rust can occur together," explains Dr. Myriam Fernandez,
a research scientist with AAFC in Swift Current, Saskatchewan. "The new
strains of stripe rust that withstand the warm dry conditions are devastating
because they infect crops early, whereas, in the past, stripe rust would not
have appeared in Saskatchewan until late in the season and so no significant
damage would have occurred. This past year, because both rusts appeared to have
overwintered in Saskatchewan, leaf rust also showed up earlier than usual in
some fields, however, the hot and dry conditions over the summer kept it in
check and stripe rust became the most prevalent."

Rust can normally be controlled with fungicides, which is a 'short-term control',
according to Dr. Kequan Xi, a researcher with Alberta Agriculture, Food and
Rural Development at Lacombe. "A better long-term control would be to breed
for resistance to the fungus," he says. Unfortunately, he adds, AC Barrie,
one of the most popular hard red spring wheat varieties grown in western Canada,
is susceptible to stripe rust according to screening done by the AAFC's Cereal
Research Centre in Winnipeg. Stripe rust has been observed as far north as the
Edmonton area and has caused yield losses in central Alberta.

There are at least three fungicides registered for control of stripe rust on
wheat or barley, which gives growers some options if they identify the problem
early enough. However, all of the researchers maintain that the best solution
is resistant varieties.

"Our wheat breeders are gearing up to find better cultivars," says
Gaudet. He concedes that even though the process has a head start with a resistant
gene already identified, the shifting nature of the rust and the length of time
it takes to get a new cultivar registered and in growers' fields may mean new
varieties will not have a long shelf life. "We do have fungicides that
work, but this new strain took us by surprise."

"Timing of fungicide application is very important," continues Xi.
"Rust develops very quickly, so there may only be a small window of opportunity
to spray for control. If growers miss that window, they could still end up with
losses on top of the cost of the fungicide." Research in Australia indicates
that spraying needs to be done before stripe rust reaches five percent of the
leaf area on the flag leaf to be effective. Seed treatments can help delay the
disease but they are not effective if the spores are airborne.

All the researchers encourage growers to scout their fields regularly, particularly
in the areas where stripe rust has been identified. Xi says if the weather is
hot and dry, nature may help with the control but field scouting is the only
way to know if this is happening.

Thus far, most of the work on stripe rust has been conducted on wheat and the
researchers have better data on what works and which varieties have some resistance.
In the case of barley and triticale, there is less information. Xi notes that
although breeding lines of barley and triticale have been screened for resistance,
there has not been much screening for cultivar resistance and he is hoping work
can begin soon.

"Growers must be diligent," cautions Gaudet. "Stripe rust has
a tremendous capacity to modify its own genetics to adapt to the available resistance."
Therefore, field scouting, proper identification, careful use of fungicides
and crop and variety rotation may minimize the effects this new breed of rust
is having on the cereal crops in the irrigated areas, in particular, of southwestern
Saskatchewan and southern Alberta. -30-