Kochia and mustard challenge lentils

In a more normal market, there are plenty of good reasons to grow lentils. But there are also two good reasons not to: the evil twins kochia and wild mustard.

Market problems or no market problems, producers are still growing lentils this year and weed control will still be the same yield-robbing problem it’s always been. University of Saskatchewan weed scientist Steve Shirtliffe and his team have been delving into various techniques for combating kochia and wild mustard in lentils.

“I call them the evil twins,” he said.

“You need to be weed-free in the five to 10 node stage. No kochia. No wild mustard. Lentils are notoriously poor competitors, but if you can get them past the 10 node stage, then they can take care of themselves pretty well. This is definitely an early season task.…

“You have to get your perennial weeds under control first, of course. And we know that annual weeds can get out of control early in the season. Once you’re in flowering in the 10-node stage, if you have a good stand, then the lentils cover the ground and they should be OK.

“Weeds developed resistance to the Group 2 herbicides very quickly. You won’t get good control with products like Solo, Odyssey or Pursuit. There’s quite a few mutations that will confer absolute resistance to those products. When Group 2 was first introduced, it was pretty much viewed as a miracle product. But first kochia developed resistance because the products were over-used. Then wild mustard became resistant. Literally any weed will develop resistance to Group 2.”

Shirtliffe said for many years farmers used Sencor on broadleaf weeds in lentils. He said it worked adequately, but timing was so critical. It had to be used early.

Early weed control is precisely what lentils need, but under some environmental conditions, it caused major damage to the crop. That’s what pushed the widespread adaptation of Group 2 products. They could be used later in the growing season without crop damage. However, nobody at the time realized how quickly resistance would develop.

He said that Sencor is still registered. If a grower uses it properly and accepts the risk, it can still be a fairly effective herbicide. There hasn’t been a lot of pressure on Sencor to foster resistance.

Also, it’s too late for this growing season, but lentil growers are having good results with fall-applied Edge for early season weed control.

“I remember when herbicide resistant mustard showed up, I took a drive out in that lentil belt around Kindersley and Rosetown and south of there. There were terrible messes of mustard in lentils. Terrible. I remember thinking, ‘heck, I can grow organic lentils and have less weeds than this.’

“So we started working with organic techniques along with conventional techniques. We looked at combining unconventional weed control methods with herbicides in order to improve their efficacy and found you can actually get some pretty reasonable control mechanically.

“We tried harrows, but we were in a no-till system, so they just plugged up with straw. That’s when we started working with the rotary hoe and inter-row tillage. They worked well in organic, but there was also evidence that they worked well in conventional weed control.”

University of Saskatchewan weed researcher Steve Shirtliffe says that to be effective, the rotary hoe should be used just after the weeds have emerged. | University of Saskatchewan photo

To be effective, the rotary hoe should be used just after the weeds have emerged. Harrowing works well when the weeds are slightly larger.

Inter-row tillage works, but there are some challenges, one of which is pulling up lumps that will interfere with harvest operations. The weeds should be left to dry up and then the field should be rolled to push the lumps back into the soil.

“I’ve seen some old research on this,” he said.

“You can roll your lentil field quite late, all the way up to pre-flowering stage. Do it on a really hot day when the plants are kind of wilting, it doesn’t hurt them very badly. The big risk is you can spread disease inoculum around the field if you roll them when the soil is wet. It’s like riding the escalator just after somebody sneezed on the handrail.”

Lentils have very low tolerance to saline soil. In fact, few crops will thrive in the saline spots in a field.

However, kochia loves salinity. It grows where nothing else will. When you spray, you’ll only kill kochia that’s susceptible to the spray. The other plants just keep on growing without competition and continue reproducing.

“These saline spots provide the source populations for herbicide resistant kochia,” he said.

“We know that’s where the resistant kochia is always found in fields. Maybe one aspect of precision agriculture should be to identify these spots and seed them to something that out-competes kochia, maybe pig grass.”

On seeding rates, he has gone as high was 560 plants per sq. metre, but that’s not economically feasible. He said that if you’re around 250 plants per sq. metre, that should provide an acceptable stand and it’s economically viable. That’s about double the previous recommended seeding rate.

“People say we’ll have disease with such high density, but remember, we were growing lentils and having disease problems in the wettest of wet years,” he said.

“Even in those wet diseased years, we had a better economic return at 250 plants. There’s some myth out there that all your lentil plants will get diseased and die at the higher rate, but it’s not true.

“Here’s what plant pathologists tell us about seeding rates. You can have a disease-free crop if you grow a single plant, all by itself, as far away as possible from any other plant. That one plant has to be further than any spores can possibly spread.

“We found you can grow a high-density crop with 250 plants, but with a more aggressive fungicide regime with two fungicide applications. In those wet years, that worked quite well.”

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