Stacked seed traits take on problem weeds in soybeans

Are multi-trait systems the answer to resistant weed battles in Ontario’s soybean crop?

When a weed shows resistance to one herbicide group, it’s a big concern. When it shows resistance to multiple groups, it’s a huge problem. For soybean growers in Ontario, resistant weeds are causing serious production issues in many areas and right now there aren’t any quick fixes. But, new seed system technology hopes to make dealing with resistant weeds in soybeans easier going forward.

“Currently, the number one weed concern for soybean growers is glyphosate resistant fleabane,” says David Kikkert, crop and campaign marketing manager, soybeans and pulses with Bayer. “We’re also seeing fleabane with resistance to both glyphosate and Group 2 herbicides along with glyphosate resistant ragweed and waterhemp. These can be big, obnoxious weeds that can significantly reduce yield and cause production issues throughout the season.”

To address concerns with weed resistance in soybeans, several new production systems in development use stacked seed traits for dual tolerance to glyphosate plus another herbicide from a different group. Roundup Ready 2 Xtend, for example, is now commercially available, and other systems are waiting for international market approval. Bayer has teamed up with MS Technologies to offer Balance GT, which, Kikkert says, should be available to Canadian growers in 2018.

“We worked together with MS Technologies in the U.S. to develop the Balance GT soybean system,” he says. “This system will bring top soybean seed genetics that have stacked resistance to both glyphosate (Group 9) and isoxaflutole (Group 27). Our new Balance Bean herbicide will bring a new herbicide group for soybean growers to use that will provide preemergent and long lasting residual control. We are also recommending that growers use more than one herbicide group in the tank to attack problem weeds like resistant fleabane.”

In order to manage difficult-to-control resistant weeds, many soybean growers combine new technology with good crop management. They’ve also tried preemergent products with residual activity in the hope of eliminating weeds when they are small. Another approach has been to take out the weeds just before harvest with PPOs. All of these have had sporadic success, but none have been the silver bullet soybean growers are looking for.

“Some of this will work, but the conditions need to be right,” says Kikkert. “For example, with most residual applications, moisture is required in order for them to maximize their performance. This year it was dry in some areas when these herbicides were being applied and it wasn’t as successful against problem weeds.”

Mike Cowbrough, weed management field crops program lead with the Ontario Ministry of Agriculture and Rural Affairs, says the new herbicide tolerant systems could help fill the gaps since all three systems currently awaiting approval take different approaches to controlling resistant weeds in soybeans. He says that his biggest concern is off-target drift, so growers will have to be cautious about how they apply the herbicides with these systems. However, he says the more options available, the better.

“I think these new stacked trait systems could be very good for weed control in soybeans. But we still have to be very careful in our weed management practices because if there is one thing we’ve learned in recent years, it’s that environmental systems will adapt,” he says. “These systems, combined with practices such as destruction of seeds at harvest, or rotation into crops like edible beans or wheat where the chemistry and weed profiles are different, will all help reduce the spread of resistant weeds.”

Historically, soybean growers have faced challenges as the crop has fewer herbicide modes of action available to it than other crops, says Cowbrough. For consistent weed control, especially when looking at herbicide resistant weeds, growers have to make the most of every option at their disposal. In addition to tank mixing and late season herbicide application, another route has been using tillage to try and remove resistant weeds before they become unmanageable.

“As Canada fleabane is a fall emerging weed, tillage can be an effective option to break up the small weeds before they go dormant for the winter,” says Cowbrough. “Many soybean growers have to do some tillage to manage corn stalks, and they see the fleabane already growing in the fall. But even when fleabane seedlings are small they can hold onto the soil even when it has been broken. So you won’t get 100 per cent control this way.”

Cowbrough adds that, currently, the best resistant weed control happens ahead of planting or prior to emergence, because once these weeds grow above the canopy late in summer, there’s no reasonable way to control them. “We have tried weed wicking at that point,” he says, referring to the process of applying a herbicide directly to the weed. “But most of those weeds are already tolerant to the herbicides registered for application at that stage, and we would only get 40 per cent control at best,” he says. “We found the crop kept on flowering and then the wind would disperse the seed, setting up another fall of management issues for the grower.”

Cowbrough says he can’t fault the process — most growers are using every management option available to try and get rid of these resistant weeds. But he says new tools are needed to complement proactive weed management in the crop.

“Several researchers in the province are looking at the Harrington Seed Destructor, which has been effective in Australia in destroying weed seeds at harvest,” he says. “This device goes behind a combine to pulverize the seed. Our concern is that Canada fleabane has very small seeds so we still need to assess if this will effectively kill the seed.”

While the new stacked-trait systems hold a lot of promise, good stewardship will always be important to keep these products working now and into the future. But some stewardship messages are more difficult to reinforce in soybeans.

“Growers know that, in general, crop rotation is an important management tool, and that holds true for the development of disease and some weeds,” says Kikkert. “But often the products used to control weeds in soybeans are also used in rotational crops, so growers aren’t changing up the modes of action, and that can help weeds select for resistance. So we need to be looking at what herbicide groups we’re using across crops to get ahead of weed species.”

Choosing a soybean system like LibertyLink is an effective way to rotate chemical groups since Liberty herbicide has no known weed resistance in Canada, says Kikkert. The initial launch of Balance GT will have two stacked traits, and will be the foundation system leading to a triplestacked herbicide tolerate system in the near future that will include varieties bred for resistance to glyphosate, isoxaflutole and Liberty herbicide.

“Corn has already seen the introduction of successful multiple stacked traits to help manage problem weeds and insects,” says Kikkert. “We hope these new stacked trait soybean systems will offer similar success for soybean growers.

“I think that these types of systems, with contact and residual control, will offer growers more flexibility and, together with good weed management practices, will help make managing resistant weeds easier,” he says. “We need to preserve all the tools we have, and make our new tools even better. I think these stacked traits systems will help do just that.” FF