Crop Advisor’s Casebook: Cleaver in canola a mystery

A Crop Advisor's Solution from the December 2, 2014 issue of Grainews

Kayla Sword is a sales agronomist with Richardson Pioneer Ltd. at Marshall, Sask.

Kayla Sword
photo: Supplied

It was the later part of June when I received a concerned call from Riley, a grower in Marshall, Sask. The grain farmer, who grows primarily canola, wheat and barley on his 5,000-acre spread, was having a problem with cleavers in his canola fields despite his use of an in-crop herbicide.

“I don’t’ think it was a good spray,” Riley said. “It might have been a bad batch of herbicide and that’s why it didn’t work.”

Riley asked me to come out and have a look. When I arrived at one of the affected fields, I could see cleavers widely distributed through the canola crop. Riley said there hadn’t been much change at all since he had applied Odyssey, a Group 2 herbicide with the active ingredients imazamox and imazethapyr, three weeks earlier.

Upon closer examination, it was obvious that most of the cleaver plants were still growing and showed little effects from the herbicide application. However, I did observe that some of the plants were display- ing purpling as well as some cupping on the leaves.

When I inquired into the growing conditions that season, Riley said he didn’t believe the canola crop had been under stress. Riley also stressed that he’d been applying the herbicide on the canola in this field the same way successfully for a number of years, always ensuring it was applied at the right rate, time and conditions, so he was at a loss to explain what was going on this season.

When I questioned Riley further about such factors as spray equipment, water volume, and application procedures, it was clear all the proper measures had been taken during the herbicide application. What then, was at the root of the cleaver problem?

Cleavers were widely distributed through the canola crop, even though Riley had applied a Group 2 herbicide three weeks earlier.

Cleavers were widely distributed through the canola crop, even though Riley had applied a Group 2 herbicide three weeks earlier.
photo: Supplied

Crop Advisor’s Solution: Herbicide resistance solves cleaver mystery

Riley didn’t believe the canola crop had been under any stress, like drought, heat or flooding, and he assured me that herbicide had been properly applied at the right rate, time and conditions — the same way it had been applied on the canola in this field for the past few years.

When I questioned Riley further about such factors as spray equipment, water volume and application procedures, it was clear all the proper measures had been taken during the herbicide application.

I began to suspect the cause of the problem, and a close examination of the cleaver plants lent support to my diagnosis. While it was clear that most of the plants were still growing and hadn’t been affected by the spray, some of the weeds were displaying purpling as well as some cupping on the leaves. This showed an early onset of Group 2 symptoms, but the cleavers were able to metabolize the herbicide and continue to grow.

Clearly, herbicide resistance was at work here, and a seed sample of the cleavers sent away for testing confirmed it. The cleaver had developed a resistance to the Group 2 herbicide after an extended period of year-after-year use.

Unfortunately for Riley, those resistant cleavers in his canola fields resulted in a 25 per cent yield loss. The grower lost even more revenue, the result of the canola crop being downgraded from a No. 1 grade (up to one per cent of cleavers permitted) to a No. 3 grade (up to two per cent of cleavers permitted).

The important lesson for Riley, and all growers, is that resistance to Group 2 herbicides is here and precautions need to be taken to stop or at least slow this growing trend.

Next season and beyond, Riley can address his cleaver problem by rotating crops as well as his weed control products to help slow down the onset of herbicide resistance.

Applying other herbicide groups as well as using a spring burn-down product, ideally a Group 12 or 14 herbicide containing glyphosate, should help control the cleaver problem by suppressing the troublesome weeds.

Kayla Sword is a sales agronomist with Richardson Pioneer Ltd. at Marshall, Sask.

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