Crop Advisor’s Casebook: Ailing canola crop a mystery

A Crop Advisor’s Solution from the September 30, 2014 issue of Grainews

Last June I received a call from Bill, a grain farmer with 8,000 acres of barley, wheat and canola in Waskatenau, Alta. Bill had sprayed his canola crop with a herbicide before going away for a weekend of fishing. When he returned home, he was alarmed to see patches within the field with damaged, stunted plants that looked delayed compared to the rest of the crop.

“I don’t understand it. I sprayed the field a week ago, when the crop was in the one- to two-leaf stage, and the problem appeared a couple days after,” Bill said, adding that plants in some of his other canola fields were exhibiting the same symptoms.

Jason Sauchuk

Jason Sauchuk
photo: Supplied

When I came out to Bill’s farm to have a look, I could see obvious signs of stunting and damage on affected plants: purpling, chlorosis and cupped leaves. There also appeared to be a distinct pattern to the damage. Bill had hoped the symptoms would clear up on their own, but that wasn’t happening.

Bill had tried a new variety of canola seed that spring, but I couldn’t see any issues with either the seeding depth or the planting speed. Bill had also tried a different fertilizer blend than he had used before, and thought that might be causing the problem. However, improper fertilization was ruled out because we’d taken a soil test the previous fall and made a fertilizer recommendation based on the results.

There were obvious signs of stunting and damage on affected plants: purpling, chlorosis and cupped leaves.

There were obvious signs of stunting and damage on affected plants: purpling, chlorosis and cupped leaves.
photo: Supplied

There was good soil moisture in the field and Mother Nature had provided excellent weather, so environmental conditions weren’t likely to blame either. As for Bill’s pesticide use, he had the right water volumes and had mixed his chemicals the right way.

Crop Advisor’s Solution: Herbicide residue

When I arrived at the farm, I could see obvious signs of damage within the canola field: purpling, chlorosis and cupped leaves. Bill told me he had sprayed a week previously, when the crop was in the one- to two-leaf stage.

Bill thought a new fertilizer mix he’d tried in the spring could be to blame.

However, that was ruled out since Bill had used the exact nutrient blend that was called for in previous soil testing. The canola seed had been planted correctly, and there didn’t appear to be anything wrong with Bill’s pesticide program. There had also been good weather recently and soil moisture was just right, so that couldn’t be the culprit either.

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As we walked around the field a little more, I noticed something — there was a distinct pattern to the damage that corresponded with the width of Bill’s sprayer. We talked about that, and Bill mentioned something that helped clue me in to the source of the problem.

Bill had bought a brand-new sprayer over the winter, and had only sprayed three different chemicals with it. When I asked him what he sprayed, he told me he did a pre-seed burnoff with glyphosate and a Group 2 tank mix before moving to in-crop canola herbicide. I asked Bill how he had cleaned the equipment before the last spray. “I did a rinse with ammonium water and flushed the booms, and then did one water rinse,” he said.

This was the source of the problem: Bill should have done a triple rinse on the sprayer before the final herbicide application to get all the residue out of the tank. Bill explained that he’d been in a rush to go fishing so he hadn’t bothered. I sent a sample of the affected canola away for testing and my diagnosis was confirmed — the crop had been damaged by Group 2 residue left in his tank from the pre-seed burnoff tank mix.

I advised Bill to change his method of cleaning the sprayer tank, making sure to triple rinse and to remove filters and clean them thoroughly between applications to ensure there was no leftover residue. I also suggested he try a different tank cleaner, or pay specific attention to what tank cleaning product and procedure is required for the herbicide he is using.

In the end, Bill was happy that we had gotten to the root of the problem, but was disappointed with the minimal yields in his affected canola fields. There was simply no recovering from the Group 2 residue damage.

Every producer should have a cleaning checklist on sprayer equipment when switching to different chemicals. Triple-rinsing the tanks, using proper tank cleaning procedures, and removing end-boom caps to flush out booms will ensure all residue is removed from previous herbicides and avoid any crop injury potential.

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