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Control of white mould not always easy in lentils

Research at the Crop Development Centre at the University of Saskatchewan in
Saskatoon has shown that controlling sclerotinia white mould in lentils with
fungicides is difficult. The researchers, using the same fungicide application
strategy for lentil as is used for control of sclerotinia stem rot in canola,
found that fungicides did not control the disease in lentils.

"In canola, the infection tends to occur on the senescing flower petals
that, when dropping and landing on green tissue, leads to infection of the canola
plants," explains Dr. Sabine Banniza, associate professor of plant pathology
at the university. "Growers will spray at flowering and get control of
the infection because flower petals remain free of the fungus. This is not the
case with lentil."

Research shows fungicide control of white mould is ineffective. Photo Courtesy Of CDC Saskatoon.

Banniza and her team investigated management strategies for controlling white
mould in lentil using fungicides and plant density. What they discovered, during
two years and in two locations, is that the infection most often affects lentils
late in the growing season, so spraying fungicides at the flowering stage is
not an effective control.

"We began by applying the same control strategies to lentils as we would
do with canola, but we discovered they didn't work," admits Banniza. "In
fact, what we learned with lentils through experiments in growth chambers is
that the flowers aren't the only way the fungus can infect the plant."

The research also showed that the plants become more susceptible to disease
as they age, leaving them more prone to disease infection in the fall prior
to harvest. "We also learned that spraying later, when the fungus is present,
is ineffective because the spray cannot penetrate the dense canopy to the lower
leaves and stems where the fungus will thrive," Banniza continues. In short,
fungicide applications did not reduce the severity of the infection and had
no influence on yield.

Mark Kuchuran, technical development specialist with BASF in Saskatoon, Saskatchewan,
agrees that getting control of white mould in lentils after canopy closure is
difficult. BASF markets Lance, a fungicide registered for control of white mould
in lentils. The label for Lance recommends application at the beginning of flowering,
with a second application seven to 14 days later if the disease persists or
weather conditions are favourable for disease development.

"In our research trials, white mould control was effective if you could
get canopy penetration. But after the canopy closed in, we saw control drop
off with later applications," explains Kuchuran.

Fortunately, white mould does not occur every season, but the ideal conditions
appear to be a dense canopy and late season rain that does not allow the crop
to dry out. According to the research, this creates an optimum atmosphere for
the fungus to attack the plant. But, by then it will be too late to spray for
control. If the autumn weather conditions are dry and the canopy is dense, white
mould is unlikely to appear in the crop.

Kuchuran says that Lance needs to be used as a preventative spray, so if the
conditions for white mould disease development exist before canopy closure,
he recommends a Lance application. "That's pretty tough for farmers to
do, to apply a fungicide without seeing any disease symptoms," he says.
"There's not much you can do, though, about the disease when it develops
later in the season as it is almost impossible to penetrate a dense lentil canopy."

Banniza says that a late season rain can be the deciding factor on whether
white mould develops. "I would have a difficult time recommending fungicide
to control sclerotinia white mould in lentils, particularly late in the season,"
she says.

Resistant cultivars are the next great hope
The answer, according to the researchers, is to breed white mould resistant
cultivars and, although this work is ongoing, there are only small successes
so far. "New options may be available with the herbicide (IMI) tolerant
lentil (Clearfield lentil) varieties," Banniza suggests. "They would
allow for seeding at lower plant density that would result in a lighter canopy
so the crop could dry out. This could prevent infections with white mould. Also,
a more open canopy may make later fungicide sprays more effective."

The researchers realize that by answering one question, they are facing several
more. With a much better understanding of how the fungus infects lentil plants,
there may be other approaches to disease management that could be tested on
lentil to control white mould. Agronomic strategies could play a role in reducing
the possibilities of infection as well.

"It's understandable that farmers are concerned about sclerotinia white
mould as a yield reducer," says Banniza. "There's no question that
severe infections affect quality and quantity." However, her research shows
there is no effective means of getting the commonly used fungicides for control
into the lentil crop at the time when the disease shows up. Fortunately, white
mould only becomes an issue in lentils late in the season and only if the conditions
are right.

While Banniza's research has answered some important questions about effective
white mould control in lentils, it also has raised more. This leaves growers
at the mercy of the weather and the hope that conditions are never right for
white mould to reduce their lentil yield – at least until new cultivars
are developed, or Banniza and her colleagues are able to develop other disease
management strategies.