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Weeds in edible beans

Growers know about weeds in corn and soybeans, but dry beans demand a strategy of their own

In farming circles, where commodity prices and net returns dictate much of the crop plans in a growing season, the rationale for choosing alternative crops can hinge on a number of factors. The need for different equipment, different diseases that might have an impact on the crop, shipping costs and the so-called “convenience” of some crops are a few of the considerations.

Weed management can be expected to be a factor in any field crop. In dry and edible beans, however, it can be huge.

Unlike corn or soybeans that are seeing threats from influxes of species like common waterhemp, dry beans are suffering from the lack of herbicide products currently available to growers. Whether it’s white (navy) beans or kidney beans, it’s getting harder to protect a dry bean crop from weed interference.

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Similar to farming on larger tracts of land, growing dry beans requires a higher degree of management skill. Contrary to some opinions, they are not a later-planted soybean but should be managed more like a vegetable crop.

A longer critical weed-free period (from emergence to R1 in some documents) and the number of herbicide products challenge those management skills, says Dr. Peter Sikkema, professor of weed science at the University of Guelph’s Ridgetown Campus. He’s been working with dry beans for nearly 25 years and in the course of 11 years of field research, he’s determined that yield losses due to weed interference is an average of 55 per cent in dry beans. Only corn — at 51 per cent — comes close, with soybeans losing 36 per cent, spring cereals 12 per cent and three per cent in winter wheat.

“It comes down to precision weed management in edible beans,” says Sikkema. “The reality is that we don’t have that many herbicides for broadleaf weed control in dry beans. In terms of soil-applied, broadleaf herbicides, there are only two — Pursuit (imazethapyr) and Permit (halosulfuron) — end of story. A farmer needs to know the market class grown in each individual field and its relative sensitivity to herbicides, the weed species composition in each field, and the strengths and weaknesses of both herbicides, and then they will know which herbicide to apply.”

Based on his research, Sikkema believes Permit to be the stronger of the two due to its control of lamb’s-quarters and common ragweed compared to soil-applied Pursuit. In contrast, Pursuit has better activity on eastern black nightshade and provides better suppression of annual grasses than Permit.

“Both of those herbicides definitely have a place in terms of weed management in dry beans, but you have to position them accordingly,” says Sikkema. He adds that the crop to be grown after edible beans is another factor in deciding which herbicide to use.

Despite weed management challenges, Sikkema contends that edible bean growers do what they do very well.
photo: Supplied

Understanding the relative sensitivity to Pursuit among the different dry bean classes is paramount, in Sikkema’s opinion. The maximum label rate for Pursuit in soybeans is 160 ml/ac. For adzukis, Sikkema is comfortable with 125 ml/ac. That’s the low rate in soybean and the only rate given in Publication 75 for edible beans.

The other factor that can create its own set of challenges is the number of classes under the heading of “dry beans.” Black beans, cranberry, otebos, pintos, small reds and white beans are all of same genus species (Phaseolus vulgaris). Within that species, those classes are further broken down according to size — small, intermediate and large. Blacks and whites fall into the small category, small reds and pintos into intermediate and cranberry and kidneys are of the large-seed types.

Then there are adzuki beans (of the genus species Vigna angularus), which Sikkema says must be treated differently than the other market classes. For instance, trifluralin (also marketed as Treflan), is safe for all four dry bean classes, yet a grower must never apply Basagran (bentazon) or Permit, post-emerge, to an adzuki bean.

By the numbers

In spite of the challenges that dry beans create, Sikkema is lavish in his praise for dry bean growers, noting they do what they do very well, and they understand the challenges and limitations they face on an annual basis. For years, he and Chris Gillard, who’s also with the University of Guelph’s Ridgetown Campus, have hosted an annual grower day for dry bean farmers at the Huron Research Station, near Exeter, Ont. The 2018 event attracted roughly 175 growers, which Sikkema believes is significant, particularly compared to other commodities across Ontario.

“They are really committed growers and your elite farmers,” he says, noting how impressed he is by their desire to learn. “They take the time to come out and learn every single year, and it’s a reflection of the type of farmers who grow dry beans.”

Despite their enthusiasm, Sikkema contends that weed management continues to be a challenging component for those who farm dry beans. The obvious observation is that the agricultural products sector invests more money on the development of herbicides in corn and soybeans than other crops. That doesn’t stop Sikkema from researching new herbicides for use in dry beans. The overall goal of the dry bean weed management program at the Huron Research Station and Ridgetown Campus is to reduce crop injury from herbicides, improve weed management, increase crop yield and increase net returns to growers.

“My goal in the weed management program is to incrementally move forward the science of weed management in dry beans, to achieve that overall goal,” Sikkema says. “We’re not going to move forward by leaps and bounds; it’s always going to be small, incremental increases.”

New directions

To help, Sikkema is looking at ethalfluralin, marketed as Edge 20 years ago and now a candidate for re-introduction by Gowan. It’s not currently available to growers, he stresses, but he’s trying to establish its fit for use in dry beans and determine whether it’s a better candidate for weed management than products currently available.

“We’ll continue to work on Permit, which was registered two or three years ago and we’re looking at different tank mixes,” says Sikkema, noting he’s even trying a four-way tank mix with existing products. “Our question is that if you get that many herbicides in the tank, do you get more crop injury or do you get better weed control and better crop yield?”

Fluridone is another product that he’s been working with. Sikkema tried it in 2016, ’17 and ’18, and used it with an eye on crop tolerance and whether it addresses the weed spectrum in Ontario. United Phosphorus Inc. has expressed an interest in revisiting whether Blazer (acifluorfen) has an adequate margin of crop safety in dry beans to warrant registration. Reflex has been registered for 15 or more years and it’s a close “cousin” of Blazer, so the rationale is that if Reflex is safe, would Blazer be safe as well?

There’s also a pre-formulated mixture of Blazer and Basagran that Sikkema is examining, and the objective is the same: is there an adequate margin of crop safety for the use of the two — sold under the trade name of “Hurricane.” Although there isn’t another “one-in-100-year” discovery like glyphosate on the horizon, it doesn’t mean Sikkema or developers with the chemical companies are not trying to find new weed management solutions for Ontario dry bean producers. They’re even looking for different practices with the goal of increasing efficacy or reducing costs.

“By registering new and improved herbicides, farmers may be able to get commercially acceptable weed control and eliminate the need for inter-row cultivation,” he adds. “Today, farmers may use the absolute best herbicide programs in terms of weed management in dry beans, and that still won’t be good enough and they’ll have to resort to inter-row cultivation to get acceptable weed control.”

The search for improved weed management extends beyond new or older actives and tank mixes: Sikkema is researching tillage practices for weed management in reduced- and strip-till practices. In the past, dry bean production has taken place primarily in conventionally tilled fields, but some growers are moving to reduced- and strip-till systems. The question there becomes whether they can manage glyphosate-resistant Canada fleabane in reduced- or strip-till dry beans, since glyphosate-resistant Canada fleabane can be controlled with tillage.

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