For the past four years, Eric Johnson and a group of public researchers across Western Canada have been investigating options for broadleaf weed control in chickpeas.
“We’ve screened a number of herbicides, many of which either weren’t effective in controlling weeds or caused too much crop damages. In some cases they were herbicides registered in other countries, but the company wasn’t willing to support the registration here,” said Johnson, a weed biologist with Agriculture Canada at Scott, Sask.
Sulfentrazone is registered in some U.S. states under a scheme similar to Canada’s emergency registration program.
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“So we knew then there was some possibilities.”
Isoxaflutole is a corn herbicide marketed in Eastern Canada by Bayer CropScience.
“They approached us about it,” Johnson said. “They knew through some of their screening that chickpeas actually had some tolerance.”
Johnson said studies have shown chickpea tolerance is quite good.
“It’s kind of a unique herbicide because there’s not that many crops that tolerate it. Corn, tame buckwheat and chickpeas are about it. We’ve tried it on a number of other pulses and they won’t tolerate it.”
The researchers’ goal is to get enough data for a minor use registration, but there are kinks to iron out first because both herbicides are residual products.
“With the carryover problem we’ve had with other herbicides, we’re trying to get a good understanding of recropping issues,” Johnson said.
“That’s the complementary work we’ve been doing as far as trying to get this registered. Really, all we have to do under minor use is claim that the crop tolerates it and it controls the weeds it says it controls. They don’t always require the recropping data, but we’re trying to have that all together so we can make recommendations to growers on this.”
Bayer sells isoxaflutole in Eastern Canada as Converge or Balance. It’s a bleaching herbicide – Group 17 – that inhibits carotenoid synthesis. As a soil applied product, it works best when 12 millimetres of rain falls within 10 days of application.
It controls wild mustard, lambsquarters, kochia, red root pigweed, shepherd’s purse and wild tomato and suppresses green foxtail. It does not control wild buckwheat and cow cockle.
While chickpeas show good tolerance to isoxaflutole, field peas, lentils and dry beans do not.
FMC sells sulfentrazone in the United States under the trade name Spartan. It is registered on soybeans, tobacco and sunflower, with a North Dakota registration for wild buckwheat control in chickpeas and field peas.
It’s a Group 14 herbicide that inhibits the PPO enzyme, which is used to synthesize chlorophyll in susceptible weeds. Western Canadian research has found that the herbicide controls wild buckwheat, kochia, lambsquarters and red root pigweed and suppresses wild mustard.
Sulfentrazone is also soil applied and requires rainfall for activation. Chickpea tolerance is very good, field pea tolerance fair and lentil and dry bean tolerance is poor.
Johnson said Bayer’s testing of isoxaflutole has prompted it to be a little concerned about the residual impact on other crops.
“They’re reluctant to go forward with registration,” he said.
“The other thing, it has some weaknesses. It doesn’t control wild buckwheat or cow cockle. With the sulfentrazone, FMC doesn’t have a presence in Canada yet, so it’s a little more of a process in order to get it into Canada. They’re looking at getting it registered on sunflowers to begin with, but we’ll have a number of possibilities for minor use registrations after that registration occurs. We’re also looking at it in flax and even field peas has some tolerance to it.”
Bayer’s concern with isoxaflutole concerns lentils planted two years after the herbicide was applied. Johnson said many chickpea growers are also going to be lentil growers and they may be interested in rotating their fields into lentils two years later. As a result, it would be undesirable if residues caused lentil damage.
“We’ve looked at spring wheat and durum wheat: there’s not a problem with them the year after,” he said. “We haven’t looked at crops like canola yet, because we’re focusing on areas where chickpeas would be grown, in cereal areas.”
He said his team has so far not found much of a problem with lentils two years after.
“If we can look at lower rates, I think they’d be a lot more confident.”
Organic matter is important with isoxaflutole breakdown. Johnson said the area where it would be used would be more likely to have dryer, low organic matter soil, making carryover more likely. With sulfentrazone, the concern is also with lentils.
“Cereals look pretty good the year after and even canola doesn’t look too bad. It’s not strong on mustard-type plants. But with lentils, we’re even finding injury three years afterwards on the soils (at Scott). The cation exchange capacity is the important thing as far as the carryover, so lighter textured soils, low clay content and low organic matter, you’re going to see more residual carryover.”
Johnson said the solution might be a mix of the two products.
“The sulfentrazone works well on wild buckwheat, kochia and redroot pigweed, but is quite weak on mustard species,” he said.
“The isoxaflutole is very strong on those. So the next step we’re working on is looking at combined low rates of each in a mix. We’re hoping that will help us manage the residue issue and provide broad spectrum weed control.”
Johnson said Bayer isn’t interested in going forward with isoxaflutole by itself in chickpea, but is interested in combinations of the two.
“We’re hoping that’s going to be where we get a nice product for growers.”
Both products are pre-emergent soil-applied products and Johnson said they would work fine in a direct seeding system because farmers can tank mix them with glyphosate.
“What I think you want to do with it is do it as part of your burnoff. If you were going to do it two or three days before seeding, it wouldn’t matter. It’s just the timing we’ve chosen is about three days after seeding.”
One concern is that poor weed control can result if there is no rainfall to wash the product into the soil after application.
