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Biocontrol of sclerotinia

Researchers making progress.


November 19, 2007
By Bruce Barker

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46aA natural control for sclerotinia in canola and dry beans may be on the horizon
if researchers at Agriculture and Agri-Food Canada (AAFC) at Brandon and Morden,
Manitoba, and Lethbridge, Alberta, keep making headway. Deb McLaren, a research
scientist at Brandon has been conducting studies on a mycoparasite called Coniothyrium
minitans
that attacks sclerotinia.

"It is a native fungus found in Manitoba in the late 1970s by Henry Huang,
around Morden," explains McLaren, who is currently conducting field studies
on the fungus. "We are seeing pretty good control in canola and dry bean
and a good reduction in sclerotia numbers."

Since the 1980s, scientists have mainly been working with fungus in sunflowers
for control of sclerotinia diseases. Research on dry beans across the prairies
began in 2002 and canola in 2004.

Sclerotinia sclerotiorum causes white mould in dry beans and sclerotinia
stem rot in canola. McLaren says that spraying chemical fungicides to protect
canola and bean blossoms can be effective in controlling sclerotinia disease,
but proper timing and effective coverage of crop canopy are necessary to obtain
adequate disease control. These conditions can be difficult to achieve and application
of chemical fungicides does not reduce the survival of sclerotia, the overwintering
bodies of Sclerotinia sclerotiorum in the fields. Biocontrol also offers
a more natural way of controlling sclerotinia diseases.

Field trials show promise
Field trials at Brandon, Morden and Lethbridge are evaluating the potential
of foliar and/or soil application of C. minitans for the control of white mould
of dry bean and sclerotinia stem rot of canola under prairie conditions.

Trials in canola started in 2004, and evaluated sclerotinia control compared
to untreated checks and a fungicide. McLaren says that foliar applications of
C. minitans at 30 to 50 percent bloom in canola resulted in less stem rot than
in the untreated control and produced results similar to the application of
Lance fungicide.

The spring soil applications of C. minitans did not provide as good a control
of sclerotinia in Manitoba, as compared to Lethbridge. "We're not sure
of the reason. It could have something to do with the environment, or soil type,
or something of that nature," explains McLaren.

Foliar control in dry bean trials also looks promising. In the trials, the
fungicide was applied at the recommended crop development stages. Biocontrol
treatments included a spring soil treatment and a foliar spray at 30 to 50 percent
bloom. Severity and incidence of sclerotinia were assessed at maturity, and
plot yields were determined.

McLaren says the results showed that the incidence of white mould of bean was
reduced with the application of either C. minitans or the fungicide in
most trials. In 2003, at Brandon, C. minitans reduced the proportion
of plants infected by an average of 32 percent. C. minitans significantly
reduced the number of sclerotia of S. sclerotiorum in harvested seed
and was consistently recovered from sclerotia produced on diseased bean plants.

"We are also encouraged by the carryover effect in sunflowers. We found
that if we applied the fungicide two years in a row, we were still finding control
in year three," explains McLaren. "A reduction of sclerotia bodies,
and the subsequent lower disease pressure would be beneficial to growers because
they may reduce input costs."

Trials may lead to registration
The research trials are laying the foundation for the registration process.
Should the biocontrol fungus prove to be reliably effective in controlling sclerotinia,
the trials would be part of the package submitted to the Pesticide Management
Regulatory Agency (PMRA) for registration. AAFC would then make a decision on
the best approach for commercialization.

"We may expand the research effort to other crops, as well. In 2004, we
had a lot of sclerotinia in peas, so we would like to see if there is potential
there," says McLaren. -30-