Crop advisor casebook: Has herbicide injury damaged 60 acres of lentils?

A Crop Advisor's Solution from the August 24, 2021 issue of Grainews

The plants on the injured 60 acres were stunted, had a thin stand and general yellowing, particularly on the headlands.
Dayna Elliott. photo: Supplied

Charles farms in Elrose, Sask., where he runs a 4,500-acre mixed grain farming operation, which includes lentils.

He called me one day and said one of his 320-acre lentil fields had taken a turn for the worse. Approximately 60 acres of the field showed what he thought looked like significant herbicide injury, while the other 260 acres were showing little to no injury.

I went out the following day and confirmed the lentils in a portion of the field looked sickly. The plants on the injured 60 acres were stunted, had a thin stand and general yellowing, particularly on the headlands. There was little concern about nutrient deficiencies due to the producer’s soil sample regime and a strong fertility program, which included both macro and micronutrients.

“I don’t understand it. The field was healthy last week before it was sprayed,” Charles said.

His sprayer operator confirmed the product was applied as per the label’s directions.

“We have been spraying lentils every year for the last 25 years. Why does my field look like it’s dying?”

The entire field was seeded at the same time and the sprayer tanks were sprayed within an hour of each other, Charles told me.

I went out into the field and noticed a distinct division in crop health from where Charles said he changed sprayer tank loads. The only exception was one pass along the headlands where the symptoms tapered off and plants were healthy again. The line in the field was straight, so I could tell it was mechanically made and not from natural causes.

I dug up some roots and saw they were healthy with no signs of injury from root rot or herbicide uptake.

Charles and I initially discussed the possibility of herbicide carryover in his tank, but we ruled this out as the symptoms appeared on the fifth field of lentils he sprayed that day and the last three products through the sprayer would not have caused this type of injury. There was no indication of herbicide leaching down into the rooting zone.

Some tissue testing was in order to determine exactly what the plants on these 60 acres had in common.

Crop Advisor Solution: Bridged inoculant causes damage to lentil crop

After I took tissue samples, Charles and I walked the field and I asked a few more questions.

I noticed the affected area was approximately 50 feet wide. It was then Charles informed me that he had a 50-foot air drill.

All clues indicated the issue had to be something that occurred at time of seeding or a compounded effect. Further inspection confirmed there was a variation in nodule size and location on the roots between the healthy and affected plants. When I asked, Charles remembered having a bit more inoculant left than he expected when finishing the field.

The tissue tests confirmed the symptomatic lentils were deficient in nitrogen whereas the healthier lentils in the field had sufficient nitrogen levels.

Why? It turned out that bridged inoculant in Charles’ drill was to blame for a stressed lentil crop. When it came time for the in-crop herbicide application, the stressed plants were unable to metabolize the herbicide as well as the healthy plants, leading to some compounding injury. The herbicide was likely also applied right around the time when the crop started to build significant vegetative growth and required more nitrogen.

When it came time for the in-crop herbicide application, the stressed plants were unable to metabolize the herbicide as well as the healthy plants. photo: Supplied

Unfortunately, the crop did not fully recover. Luckily the bridged product only happened on the last 60 acres of the field so marginal financial losses were experienced.

I recommended Charles make sure to inspect his crop throughout the season, not only when issues arose. I also reminded him of the best management practices of inoculants, particularly when humidity is higher at seeding.

Dayna Elliott, PAg, CCA, works for Richardson Pioneer Ltd. in Elrose, Sask.

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