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Knowing the history of your field can be your most important tool when trying to diagnose an agronomic dilemma. As Landon, a farmer from Earl Grey, Sask., experienced first-hand, past activities can shape a plant’s interactions with its environment, and ultimately, the crop’s development.

In the spring of 2011, Landon had planted two fields with canola. By the end of June, one field was producing normal, healthy plants, while, across the road in an adjacent field, the plants were stunted, yellow and wilted. “Something’s affecting the vigour of my canola,” he said. He thought that low fertility, disease or damage from insects could be causing the problem.

At Landon’s farm, I immediately ruled out insects and disease as the causes of the damage to his canola stand. There were no insects present in the field or disease pressure on the crop that could have caused the extensive damage I observed. Environmental factors may have added stress to the crop early in the spring, but the majority of the excess water had already dried up. Besides, any symptoms caused by environmental factors would have affected both fields, not just one.

The same fertilizer type and rate had been applied to both fields. The soil type, consistency and moisture were also similar in both fields. One field had been planted with glyphosate-tolerant canola, which produced the yellow and wilting plants, and the other had been planted with glufosinate-tolerant canola, but I didn’t think the difference in variety was the issue.

I asked Landon what he’d planted the previous year. “Wheat in the unaffected field and Clearfield lentils in this one,” he said, pointing to the damaged field.

“And you applied the registered Group 2 herbicide to the Clearfield lentils?” I asked.

“I sure did,” he replied.

“Well, the bad news is that your plants are suffering from herbicide carryover, but the good news is that your crop could recover with a little cooperation from Mother Nature,” I said.

Chemical residue from the Group 2 herbicide had caused the stunting of growth and wilting of Landon’s plants as well as the yellowing of their leaves. Planting non-Clearfield canola the year after the use of some Clearfield chemistries is not recommended.

To keep history from repeating itself, I recommended that Landon include more detail in his field records. In addition to crop rotation plans, include all pesticide applications and rates, and check re-cropping restrictions prior to planning the next year’s crop. Knowing re-cropping restrictions of residual herbicides is important when deciding upon a future crop rotation. Without that information, there’s a risk of antagonizing the crop with herbicide injury. In fact, one option that was open to Landon was the use of non-residual herbicides with his Clearfield lentils, which would have allowed him to re-crop to canola without any issues. More proactive planning, or the development of a crop plan with his agronomist, may have prevented the problem from occurring.

Although it was too late to implement these management changes for this field, the weather continued to be conducive to good crop development, and Landon continued on into the growing season with positive agronomic activities, such as fungicide application and correct swath timing on both fields. The stressed field grew out of the residue setback as it advanced, looking healthier as the summer pushed on.

We compared the yields of the two fields at harvest and the difference was minimal! The unusually wet spring had worked in favour of the field’s recovery by washing some of the residue from the soil. All things considered, Landon was fairly pleased with this outcome. †

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