Top Crop Manager

Features Desiccants Seed & Chemical
Treat edibles like a vegetable crop

Successful control depends on precision.


November 13, 2007
By Top Crop Manager

Topics

24aEdible beans are making a comeback. Whether it is a reflection of pricing in
other commodities or a means of avoiding soybean diseases and insect pests,
more growers seem to be turning to edible beans. There are more fields of edibles
in mid-western Ontario, and even in the Essex-Kent region.

But if growers are not familiar with contemporary realities of growing edible
beans, they need to correct those shortfalls before heading back to the fields,
particularly with weed management strategies.

Dr. Peter Sikkema, professor and weed management specialist at Ridgetown College,
emphasizes that any discussion of weed management programs in edible beans must
be preceded by the word 'precision'.

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Much has changed
In the past decade, the soybean industry has seen the emergence of more varied
types of food-grade soybeans. Miso and natto beans are being grown across much
of southern Ontario, but they are still largely treated the same as conventional
soybeans in respect to weed management. Not so with edible beans, says Sikkema.
"The optimum weed management program for cranberry beans is different than
white or black beans, which is different than for adzuki beans," he explains.
"It's very important for growers to appreciate that they have to develop
precision weed management programs for edible beans. The weed management program
must be adjusted depending on market class grown, weed species present, weed
density and soil type, to minimize crop injury, optimize weed control and maximize
profit."

To help, Sikkema suggests growers treat edible beans more like a vegetable
crop than a field crop, adding growers should never draw parallels between soybeans
and edible beans. "You have to be prepared to put on your leaf hopper applications,
you have white mould to worry about and you may have to use a desiccant before
harvest," says Sikkema. "You have to be prepared to use low rates
of herbicides, accept the fact that if you're going to use those low rates,
you're going to have the possibility of weed escapes, and then you have to be
prepared to address them, possibly with a post-emergence grass or broadleaf
herbicide or inter-row cultivation."

But the economic benefits for that higher management requirement is obvious
when considering a solid yield of 20 bags per acre, a price of $30 per bag and
a gross of $600 per acre. With $7.00 per bushel soybeans and a high yield of
50bu/ac, that per acre gross is $350.

Precision, precision, precision
Before harvest can begin, however, Sikkema comes back to the 'precision' in
precision weed management programs. Since edible beans are not as resilient
as soybeans, there is a greater risk with compounding stresses. Soil compaction,
root rot diseases like rhizoctonia or pythium, cool wet springs and poor seed
quality can combine to cripple a field of adzukis, whites or cranberries. All
the more reason why growers must be precise in their herbicide program. "The
best example is Pursuit (imazethapyr) which is the backbone for annual broadleaf
weed control," says Sikkema. "Small seeded edible beans such as white,
black, pinto or otebo beans have a narrower margin of crop safety and the rate
of Pursuit should be reduced to approximately 75ml/ac."

As the seed side increases, so too can the rate, to 100ml/ac for kidney, cranberry,
yellow eye or brown beans. Adzuki beans are the most tolerant to Pursuit and
the full 125ml/ac can be used. If growers use reduced rates of Pursuit, it is
recommended they tank-mix with one of the pre-plant incorporated grass herbicides.
Also, they must be aware of the potential for weed escapes and be prepared to
address them with the use of either Basagran or Reflex applied post-emergence,
or inter-row cultivation.

Timing is another consideration, says Sikkema. "If you look at products
like Dual (S-metolachlor) or Frontier (dimethenamid), they're just safer when
you apply them pre-plant incorporated than when you apply them pre-emergence,"
he says. "In years when you get a heavy rainfall just when the beans are
cracking through the soil surface, they take up a more than normal amount of
the herbicide which may result in crop injury if you put it on pre."

Treflan (trifluralin) and Eptam (EPTC) can only be applied pre-plant incorporated,
making that a non-issue to Sikkema. "If it's dry, you want to delay the
planting of dry beans after a ppi application of Eptam. Treflan is a very safe,
cost-effective annual grass ppi herbicide," says Sikkema, "The problem
is, it doesn't provide any nightshade control, or nutsedge control that you'd
get with Dual or Frontier, so again, a grower has to adjust his weed management
program depending on what his weed spectrum is and the market class that he's
growing."

In adzuki beans, there is the potential for crop injury with Eptam, Dual or
Frontier, which will damage the bean. "In adzuki beans, your only soil-applied
options are Treflan and Pursuit," he says.

In other market classes, Sikkema would make a case for using either Eptam,
Dual, Treflan or Frontier, and adjust the selection based on the weed species
composition in the field, then adjust timing to give the largest margin of crop
safety.

One final note: Never use Basagran (bentazon) on adzuki beans. "Basagran
is safe on all the other market classes but it just hammers adzukis," says
Sikkema. "Eptam, Dual, Frontier, they all hit adzukis, but the flip side
is that adzukis have the greatest tolerance to Pursuit, and the other market
classes may be injured by Pursuit."

Which is why Sikkema repeats there is no 'one size fits all' mind-set when
it comes weed management in edible beans. Precision is the key. -30-