Features Agronomy Soybeans
Edible beans a growing target for bugs and viruses

Since 2003, researchers and extension personnel have told soybean growers the
days of simply planting and harvesting their fields, worry-free, are gone. Between
soybean cyst nematode, soybean aphids and the eventual arrival of Asian soybean
rust, growers will have to be more diligent.

Now, edible bean growers are in much the same position. Bean common mosaic
virus has shown it can have a wide-ranging impact and create a similar sense
of urgency.

At the 2006 annual meeting of the Ontario White Bean Producers and the Ontario
Coloured Bean Growers' Association, Mike Donnelly-Vanderloo, a grower from Thorndale,
Ontario, told the gathering of his frustrations with bean common mosaic virus.
He described one field that showed puckered light and dark patches on leaves
sweeping through the field from 'corner to corner'. Of greater concern, however,
was that it was unclear whether it was a seedborne or insect vectored outbreak.

Nearly 12 months later, Donnelly-Vanderloo is still uncertain. "Initially,
our big concern was that the virus was in the seed," he says, referring
to conversations with provincial specialists on the subject. "Further analysis
was trying to determine if it was, in fact, in the seed or if it was borne by
a vector, meaning it came in after the crop had been planted."

Donnelly-Vanderloo also consulted with his seed source, Ron Tingley from Seedgrow
in Meridian, California. Tingley told him of a case of otebo beans in Michigan
that had been hit with the virus. "Our problem was that we couldn't prove
beyond a shadow of a doubt whether it came from seed versus an insect vector,"
says Donnelly-Vanderloo. "I have some experts saying that it was highly
unlikely to see a whole field have that much virus in it if it came from an
insect. But then others had some tests that showed positive for bean common
mosaic virus, so it's not clear cut by any means."

Concern goes beyond the disease
One thing is certain: edible beans are more 'appearance sensitive' for buyers
than soybeans destined for the crush market. Although bean common mosaic virus
was not as prevalent in 2006 as the year before, growers cannot afford to lower
their guard. "These beans are marketed on the basis of quality and visual
appearance," explains Donnelly-Vanderloo. "Visual appearance factors,
insect pockmarks, disfigurations or discolourations, are critical."

All the more reason, he adds, why growers must be diligent. The physical appearance
facet is working its way into contracts, including processing company representatives
scouting growers' fields, a reality of today that did not exist a few years
ago.

For Tracey Baute, the advice on diligence and scouting makes sense for any
field crop, and she has been emphasizing that theme for several years. Just
as soybean aphids can be worse from one year to the next, bean common mosaic
virus is just as variable. Planting dates, emergence and how those field conditions
relate to the cycle of an aphid infestation can have a significant impact on
the spread of a virus. "With soybean aphids, if you're bordering a soybean
field, aphids will test any kind of plant to see if it's a soybean or if it's
a host that it likes, so it has the tendency to transmit a disease that it picks
up," says Baute, field crops entomologist with the Ontario Ministry of
Agriculture, Food and Rural Affairs in Ridgetown.

That lends itself perfectly to the need for growers to plant certified seed.
Since disease transmission is relatively easy, the need for certified seed is
that much greater. "It's a matter of ensuring that we're planting clean
seed that's virus free so it reduces the amount of virus that aphids will come
across and transmit," says Baute. "They already came across some in
the weeds that they happen to probe, too, and that alone we can't control. But
at least we can control something like certified seed."

Uncertainty of source continues
For Albert Tenuta, the importance of determining the source of the virus cannot
be under-estimated. Like anthracnose or SCN in soybeans, bean common mosaic
virus is present in any given year. And if concerns regarding global warming
become a reality, disease management will become more important for growers.

"One of the focusses that many of the soybean breeders as well as the
dry bean breeders are following, is incorporating more resistance or genes for
resistance to many of the common viruses," says Tenuta, field crop pathologist
with OMAFRA, also in Ridgetown. "One of the important things is determining
how significant these are in terms of problems, so the breeders can get the
varieties with good resistance or tolerance."

From his perspective, Tenuta cites Donnelly-Vanderloo's 'corner to corner'
scenario as a seedborne problem. However, he quickly qualifies that by saying
there is a great deal of uncertainty due to the number of wild hosts for many
diseases. "If you have a field with uniform distribution of some of these
alternate hosts, like a weed, and you have insect vector populations, you can
get pretty good distribution across the field, as well," says Tenuta.

Depending on the time of year, some could come from alternate hosts, some from
insect vectoring and some early-season, low population levels in the seed. "That
is another issue. These viruses, in terms of visual symptoms on the plants themselves,
look like so many other things that can give you mottled, crinkled, mosaic or
yellow coloured plants." -30-