Controlling cleavers without quinclorac

With quinclorac off of the herbicide menu, farmers will need to use other tools

Last spring, the Western Grains Elevator Association (WGEA) and the Canadian Oilseed Processors Association (COPA) advised growers that they would not accept quinclorac-treated canola grown and harvested in 2016. The reason for this announcement was to make sure that grain shipped to customers in other countries remains in compliance with regards to Maximum Residue Limits (MRL). Fortunately, cleavers can be controlled without the use of quinclorac.

When grain exceeds the MRLs of other countries Canada’s reputation as a supplier of quality grain is in jeopardy, said Wade Sobkowich, executive director of the Western Grain Elevator Association. A high amount of canola is exported to China, and China does not have a MRL in place for quinclorac, meaning that the MRL is effectively zero, Sobkowich explained.

“The costs of keeping quinclorac-treated canola segregated throughout the Canadian handling system is very high,” he said. “Our Chinese customers will not pay for these added costs, nor do we believe producers should pay for these added segregation costs. Grain companies had no control over the registration or premature commercialization of Clever, and likewise we do not feel we should pay these costs either. As a result, our members have individually taken the decision to not accept canola treated with quinclorac.”

Tips for control

An annual and winter annual weed, cleavers can have a negative impact on canola and pulse crops. While crop loss data in cereals is unknown, according to Dow AgroSciences, a 20 per cent yield loss per 100 plants per square meter is possible in canola. Cleavers is particularly problematic in canola because it is difficult to separate from canola seed. Even a few seeds can seriously downgrade canola.

Ian Epp, a northwest Saskatchewan agronomy specialist with the Canola Council of Canada says boht his and the Council’s approach to the management of cleavers is systematic. “It starts before you’re planting canola, making sure that you’re prioritizing cleaver control in your cereals,” he said. “We have some really good options — some of the Group 4s, like fluroxypyr — we have really good pre-seed options,” he said. “So we can really hammer cleavers in that cereal, reduce the amount of seed going into that seed bank, and get a leg up in canola.”

The next step to controlling cleavers is making sure to get the winter annuals controlled in the fall. “The winter annuals are the biggest concern because by the time we get into canola, they’re really big and they’re really hard to control — almost impossible to control in crop,” he said.

In the fall, cleavers will be small, so they should be relatively easy to control.
photo: Ian Epp, Canola Council of Canada

In the fall, cleavers will be small making them relatively easy to control. And you can control other common winter annuals at the same time. If a few weeds do escape or weeds begin emerging early in spring, pre-seed control will be important.

Using a higher rate of glyphosate is becoming a little more common, said Epp. “But this is one where that normal rate of glyphosate that might kill most of your other small weeds might not be effective on cleavers,” he said. “So using a higher rate of glyphosate is the first thing you can do.”

Canola growers are, unfortunately, at a bit of a disadvantage in terms of tank-mix options, pre-seed. Clomazone, a Group 13 pre-plant, is one that was just registered last year. “The key with Clomazone is that it won’t help cleavers that are already germinated and up, but it will help those with the soil-activated herbicide, so it will reduce the vigor and the emergence of cleavers that crown,” he said. “You get control on the flushing of cleavers.”

In crop control options are effective, but only to a certain degree. Clearfield works well, as long as you don’t have Group 2-resistant cleavers. “Group 2-resistant cleavers are fairly widespread, especially in the black soil zone, and especially if growers have a history of applying a lot of Group 2s,” said Epp.

Liberty, he said, has a history of not working well in cleavers. “The efficacy in cleavers is kind of hit and miss,” he said. “The key is to spray early. Any of these herbicides work better when the cleavers are small.”

Luckily, with both the Liberty and Roundup systems there is the option to spray twice. “The key is to spray early and then re-evaluate, and then maybe, likely, spray a second pass in that four to five week stage,” he said. “And then you control all your weeds in that really critical period of weed control, which really affects yield the most.”

A future for quinclorac?

China could have an MRL in the near future, said Sobkowich, but no one knows for certain. “We cannot operate based on some undefined future MRL that may be approved at some unknown future time,” he said.

Furthermore, Epp notes that while quinclorac is efficacious, it is already seeing resistance, so even if the MRL issues are addressed, it may not be a viable solution.

China has not set a maximum residue limit for quinclorac in canola, meaning the rate they will tolerate is effectively zero.
photo: Ian Epp, Canola Council of Canada

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