Top Crop Manager

Features Agronomy Cereals
As edible beans increase, so does anthracnose

Appearance and production the key issues.


November 13, 2007
By Top Crop Manager

Topics

12aAs edible bean acreage in Ontario has increased since the early 2000s, anthracnose
has come more into focus for growers, researchers and extension personnel. The
threat anthracnose poses is arguably more significant than in other field crops.
Edible beans are more readily processed for food use than either corn, soybeans
or wheat. In fact, in terms of weed management, growers have been advised to
treat edible beans more like a vegetable crop than a field crop.

There are other factors that are playing into the edible bean industry. More
growers, tired of losing money on corn and perhaps looking to avoid the disease
and pest problems of soybeans, are looking for alternatives, including edible
beans. But the familiarity aspect of growing navy beans or cranberry or kidney
beans is where some growers are stumbling.

And then there are the challenges of anthracnose.

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For Chris Gillard, dealing with anthracnose can take shape on a number of different
fronts. As a college professor and researcher in edible beans at Ridgetown College,
Gillard notes anthracnose can affect the seed, leaf tissues, stems, pods and
ultimately the harvested product. Its slow growth is deceiving, but very weather-oriented.
Cool wet summers like 2004 can cause anthracnose to march across entire fields,
precipitating a plow down to prevent further spread, or rejection of an entire
field.

Appearance is important
Unlike fusarium in wheat, there is no toxin produced by anthracnose in edible
beans that endangers human health. But since it is a product that moves directly
from field to processor to consumer, growers can ill afford to have blemished
navy beans. "In 2004 we had quite a dramatic problem with anthracnose and
it came in very late in the season, so it didn't have an impact on yield,"
details Gillard. But some processors in the United Kingdom were using clear
sauces. "The blemishes on the beans weren't as easily masked in a clear
sauce as they would be in a tomato sauce, so there were shipments that were
refused when they got over there."

As a result, Gillard says there was a significant effort on the part of the
industry in 2005 to monitor the progress of the disease. As it turned out, anthracnose
was not a large-scale problem, particularly with the season's hot, dry weather.

Another part of the puzzle in dealing with anthracnose is the discovery of
a new race in 1999, designated as Race 73. "It was documented mainly out
west and then in Ontario, and it's been creeping in ever since," says Gillard,
adding that Manitoba has had greater difficulty battling the disease because
growers there rely more on bin-run seed. He also cites the seed production industry
for part of the problem.

"The seed multiplication system wasn't doing a good enough job in the
past. There were too many years of seed multiplication in Ontario, which has
a humid environment. This has promoted disease development in pedigreed seed.
Then we get a wet year like 2004 and all of a sudden you have a problem. Since
2004 companies have been doing more seed multiplication in dry environments
like Idaho and using new foliar products like pyraclostrobin (Headline) and
azoxystrobin (Quadris) to help producers clean seed.

Identification also a problem
Mis-diagnosing the disease is something Gillard also criticizes, and he speaks
from experience. He notes agronomists and extension personnel mistake the vein
discolouration on the leaves with Group II herbicide injury. "One of the
things I've learned is if you find a spot in the field, flag it and keep an
eye on it," he explains. If symptoms worsen and move from stems to leaves
to pods, then it is likely anthracnose.

Edible bean growers must follow the same advice as soybean growers dealing
with soybean cyst nematode: Get in the field and scout! In the case of anthracnose,
growers should be looking for streaking on the stems, then darkening of the
veins on the underside of the leaves. In late season, pods can become blistered,
with large grey or even pinkish craters, surrounded by blackened rings. Growers
often mistake these for sun scald, ozone damage, bacterial blight or herbicide
injury. "You see the lesions and you'll see the hot spots in the field,
but by then it's too late," says Gillard. He adds it can spread on tractor
tires, pant legs, animals or running water moving from one field to another.
In his research plots at Ridgetown College, Gillard has bio-security protocols
in place, including a decontamination process when leaving the field.

How to manage
According to Brian Hall, edible bean and canola crops specialist with the Ontario
Ministry of Agriculture, Food and Rural Affairs, anthracnose in white or navy
beans is a higher risk than with cranberry or kidney beans. Much of the seed
production for coloured beans is done in Idaho and Wyoming, where the climate
is comparatively dry. "It's not that they never see it in coloured beans,
because they are susceptible," says Hall. But in white beans, the seed
production is carried out in Ontario and Manitoba, where humidity levels are
notably higher. "We have to go back to the production side, be vigilant
and reduce the risk from year to year."

He notes that seed treated with DCT (Diazinon, Captan, Thiophanate-methyl)
and growers knowing the source of their seed are two important measures in dealing
with anthracnose in the short-term.

Hall agrees with Gillard that Manitoba is having to deal with higher incidences
of anthracnose. "Because they haven't given it the attention it really
deserves," he says. "Fortunately, it's a disease that, with good management,
can have its effect minimized. But I view anthracnose as a very serious disease
because it can completely devastate a good crop of edible beans, and that's
evidenced by the fields we've seen in the past couple of years having to be
plowed down."

Hall also advocates a move to a less reactive approach in responding to things
like the discovery of Race 73, noting that while incorporating resistance into
breeding programs is vital, other long-term options must be explored.

The latest research
To that end, Gillard refers to a funding proposal done in April 2005 which garnered
nearly $500,000 for research projects. In addition to overwintering and rotation
studies, Gillard says the industry is looking at some advanced technological
solutions. An idea is being studied to determine the genes that are unique to
each race of anthracnose. It is conceivable, says Gillard, that by selecting
the right two genes using molecular markers, it would be possible to convey
resistance that covers 98 percent of the known races.

The other long-term project is the development of a rapid identification test
to determine the presence of anthracnose. At present, it can take days or weeks
to identify anthracnose in a laboratory, with a bevy of trained personnel doing
the work. With this method, a DNA strand first must be extracted and identified
as being unique to anthracnose. Then a simple test to confirm the presence of
the DNA can be completed in one or two days, without the same reliance on personnel
or the potential for mis-diagnosis based on visual symptoms.

"They've done this with other diseases and they have been quite successful
with some," says Gillard, adding that a post-doctorate student from China
has been hired to do that work during the next three years. -30-