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Crop Advisor’s Casebook: What’s holding up this canola’s blooming stage?

A Crop Advisor's Solution from the May 16, 2017 issue of Grainews

Samantha Sentes.
photo: Supplied

Kyle farms 2,000 acres of canola, oats and peas west of Yorkton, Sask. He called me the first week of July, last year, when he discovered part of his canola crop wasn’t flowering with the rest of the field.

Kyle thought perhaps environmental factors, seeding issues or nutrient deficiencies could be stressing the crop. The plants adjacent to the road were developmentally delayed when compared with those located in the rest of the field. In fact, the plants in the field’s inner region were already starting to bloom, while the plants in the perimeter remained green and weren’t nearly as tall, he said.

Also, some of the plants’ leaves were yellowing, and the smaller leaves around the main stem were purpling, Kyle said, although he wasn’t sure when the symptoms began because they weren’t noticeable to him until the crop began to bloom. These symptoms warranted a visit to Kyle’s farm.

Upon approaching the field, I could see the bright yellow blooms of healthy canola plants surrounded by a perimeter of green plants, which hadn’t reached the flowering stage.

The area of affected plants included the entire outside round and back side of the field, with a sharply demarked boundary which included straight lines.
photo: Supplied

Walking into the field, I noticed some of the leaves on the affected plants were turning yellow, and the smaller leaves around the main stems were purpling. The growing points, as the plants were beginning to bolt, also looked damaged — they were yellowing, and the flowers looked odd.

Kyle asked if environmental stress, seeding issues or a nutrient deficiency could have caused the plants’ delayed maturity around the perimeter of the field. He also suspected something had gone wrong with his sprayer, since he’d recently applied an in-crop, Group 10 herbicide to the herbicide-tolerant canola crop.

The area of affected plants included the entire outside round and back side of the field, notably with a sharply demarked boundary which included straight lines, a pattern not typically found in nature, and exactly corresponding to the sprayer’s first pass. However, before focusing on potential sprayer issues, I wanted to address Kyle’s other concerns.

For example, stress placed on plants by inclement weather can include yellowing or purpling of leaves, but I would not expect to see the damaged areas marked out in straight lines like this.

Furthermore, although seeding canola too deep can delay maturity, seeding issues didn’t play a role in this case because Kyle’s seeder settings were correct and the machinery was working properly. I would also expect to see a more uniform distribution of affected plants with a seeding depth issue.

The growing points looked damaged. They were yellowing, 
and the flowers looked odd.
photo: Supplied

In addition, if too much fertilizer is applied at seeding and has harmed the seed, or too little is applied, resulting in a nutrient deficiency, I would expect to see symptoms across the field and not in such a specific pattern. Although the drill could have been plugged for the outside round and back side, I thought it unlikely.

Leaf chlorosis is also a symptom of a nutrient deficiency, but, again, it didn’t fit the pattern in this field.

The damage pattern did correspond exactly to the area Kyle sprayed with his first tank of herbicide — a full round of the field and across the back side — ending at the spot where he changed tanks.

I asked Kyle what crop he’d sprayed before moving to this field.

His answer: a cereal. That’s all I needed to know.

Crop Advisor’s Solution: Canola hung up on herbicide residue

For me, this was confirmation that the symptoms exhibited by the injured canola plants were caused by Group 2 herbicide residues in the sprayer tank.

Group 2 herbicide injury is a common problem in canola fields. Using proper tank cleanout procedures between different crops is essential to prevent sprayer contamination. Kyle cleaned his tank between herbicide applications, however, he must have missed some of the Group 2 herbicide residues.

Although there are many guidelines on tank cleanout procedures, the use of strong detergents, ammonia and multiple rinses is important. In addition, remove and clean screens, nozzles and filters to prevent herbicide buildup in these areas.

Proper tank cleanout procedure is repetitive and time-consuming, but protecting the next crop from injury is worth the effort. Pay special attention to tank cleanout when using polyethylene tanks, as chemicals can become etched into the tank walls, making chemical products harder to remove.

In addition, some herbicides, such as Liberty (Group 10), are known to act as strong detergents, which can pull the smallest amounts of residue

out of sprayers, even after proper rinsing, and particularly when the components are polyethylene-based materials versus those composed of stainless steel.

In the end, Kyle’s injured canola plants didn’t die, but maturity was delayed. Yield in that portion of the field was also affected and was lower than the uninjured area. Rigorous and thorough cleaning of sprayer tanks may take more time, but saves crops from injury.

Samantha Sentes works for Richardson Pioneer Ltd. in Yorkton, Sask.

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