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Crop advisor casebook: What caused the malformed pods in Chad’s canola crop?

A Crop Advisor's Solution from the February 13, 2018 issue of Grainews

Rose Boughton. photo: Supplied

Chad, who owns a mixed grain and cattle farm near Togo, Sask., noticed something was not quite right with his canola crop. It was early August 2016 when Chad contacted me about malformed pods on the upper portion of his glyphosate-tolerant canola plants.

“The pods don’t look right,” he said. “They’re all twisted up and not making seed properly.”

Chad said he’d only noticed the damage recently, at the early podding stage. I headed out to Chad’s farm to have a look for myself.

In the field, the malformed seed pods occurred on the upper third of the plants. Some of these damaged pods were stunted, while others were twisted and curled. The pods had a reddish tinge to them and were scabbed; also, some plant stems had scabbing on them.

Almost all pods had poor, if any, seed set.

The malformed seed pods occurred on the upper third of the plants. Some of these damaged pods were stunted, while others were twisted and curled. photo: Supplied

The last week had been hotter than usual, at least 28 C or more, so sunscald could have caused the discolouration. Sunscald causes purpling on the plant stems and pods during times of heat, or other, stress. However, the pods’ undersides remain a normal colour when suffering from sunscald.

In this case, the damaged pods’ undersides had a reddish tinge to them — the same colour as the rest of the pod — so sunscald was not the problem. Although I did find a few pods, here and there, with sunscald, that kind of stress would not cause poor seed set or the twisting or curling of pods.

Additionally, there were no visible exit holes on the pods, ruling out weevil damage. In fact, there was no biting, chewing or stripping damage at all, eliminating insects as the cause of damage.

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It was possible the pods were damaged by chemical residue hung up on the sprayer tank’s walls. When I asked Chad about his tank clean-out procedures, this theory seemed unlikely. Chad diligently triple rinses his sprayer tank. In addition, he didn’t use any chemicals that were prone to adhering to tank walls.

Also, this field was sprayed last, following glyphosate applications on other glyphosate-tolerant canola fields. None of the other fields showed any signs of herbicide injury. Furthermore, the glyphosate would have scrubbed out any chemical residue hung up in the tank before spraying the field in question.

We examined the field for a pattern to the damaged pods. It was this pattern that confirmed the cause of the discoloured, malformed pods.

Crop Advisor’s Solution: Malformed canola seed pods a result of chemical drift

The real clue to the cause of the malformed, discoloured pods was the damage pattern. The finger-like area of damaged plants, which worsened closer to the road and improved toward the back of the quarter, is characteristic of chemical drift.

The twisted stems and malformed/aborted pods indicated the plants’ natural growth processes had been interrupted, which is what chemical injury does to plants.

When I revealed my suspicions to Chad, he told me earlier that summer, when his crop was at the three- to four-leaf stage, a neighbouring herbicide-tolerant canola crop was sprayed with a Group 10 herbicide on a windy day. Now, there was no doubt in my mind about the cause of plant injury.

We examined the location of the neighbour’s field in relation to Chad’s, to determine if it was possible for the Group 10 herbicide to drift onto Chad’s glyphosate-tolerant canola crop. Given the right wind direction and speed, I thought it was not only possible, but likely.

Chad keeps excellent records. He could tell me the exact day the suspected drifting event occurred. Knowing the event’s date, we checked the wind speed and direction. The conditions were conducive to chemical drift.

Furthermore, Chad had records indicating he had contacted the individual who sprayed the Group 10 herbicide that day. The evidence was convincing — the damage to Chad’s canola crop was caused by chemical drift.

I sent samples of the damaged plants to a laboratory to be tested for traces of glufosinate ammonium, the Group 10 herbicide’s active ingredient.

The test results were inconclusive because so much time had passed between the incident and the analysis — the plants had long since metabolized the chemical.

At harvest, the areas of the field hardest hit by the chemical drift yielded about 25 bushels per acre compared with a field average of 50 bushels per acre.

It was odd the plants didn’t exhibit symptoms until the early podding stage, since glufosinate is a contact herbicide and kills what it touches. Plant damage symptoms should have occurred soon after the plants were exposed to the herbicide.

It is possible for glyphosate-tolerant plants to metabolize small amounts of glufosinate. However, the natural growth pattern can be altered in those plants most affected by the chemical, causing failure to set seed properly, which ultimately results in yield loss.

It’s necessary that all producers stop spraying herbicide when it’s windy. It’s also important to pay close attention to the damage pattern to determine if it’s consistent with chemical drift.

Furthermore, if a producer suspects a crop has been drifted, samples of the affected plants should be taken and sent for analysis as soon as possible, to document proof of exposure to the chemical.

Rose Boughton works for Richardson Pioneer Ltd. in Kamsack, Sask.

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