Crop Advisor’s Casebook: What’s stressing these lentils?

A Crop Advisor's Solution from the August 29, 2017 issue of Grainews

Angie Berner, PAg.
photo: Supplied

“I have never seen anything like it in 15 years of growing lentils,” Vaughn, a southern Saskatchewan producer, told me after he discovered yellowing, unhealthy-looking lentil plants in his field the week of June 23, 2016.

Our office had already received several calls from Assiniboia-area growers with similar concerns. Producers had also dropped off samples of affected plants, which included both red and green lentils.

“I sure hope it isn’t a new disease, or something that was hung up in my sprayer tank,” said Vaughn.

I headed out to Vaughn’s 3,200-acre grain farm that afternoon, where he grows durum, lentil, canola, chickpea and soybean, to determine what was causing the plant injury. While in the field staging the crop for fungicide application timing as well as checking the efficacy of a graminicide application made two weeks earlier, Vaughn had noticed the affected plants.

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In addition to leaf tip yellowing/whitening, other symptoms included wilting and rolling of the leaves, although all other plant parts appeared to be healthy. Some plants had more affected leaves than others, however, there was no pattern to the affected plants or the location of the injured leaves on those plants. For example, the top leaves were affected on some plants, while the middle leaves of others were exhibiting symptoms.

Upon inspection, plant roots looked healthy and nodulation was good, indicating normal nitrogen fixation.

The random distribution of affected plants occurred throughout the entire field. Also, more than one of Vaughn’s lentil fields, and several neighbouring fields, were presenting symptoms.

In addition to the graminicide application two weeks earlier, another important factor to consider was several severe rain storms had passed through the area 10 days prior to my visit, bringing high amounts of moisture.

Upon inspection, plant roots looked healthy and nodulation was good, indicating normal nitrogen fixation.
photo: Supplied

Vaughn thought disease was a good bet as the cause of the yellowing, wilting leaves, given the recent high precipitation levels. He also considered residue contamination in the sprayer tank due to improper tank clean out as the problem, when he switched from spraying canola to lentil fields.

However, the damage was not consistent with chemical injury from residue left in the sprayer tank. There was no distinct pattern to the affected plants, particularly straight lines separating healthy and unhealthy plants. In fact, there was no noticeable area where the plant damage differed in severity.

We scouted several areas of the field and all showed the same random distribution of symptoms. Also, Vaughn’s spray tank clean-out procedure was adequate. Furthermore, after reviewing the history of all chemicals applied to these fields for the past four years, it was unlikely we were dealing with soil residual herbicide carryover issues.

While scouting, we also established efficacy and crop tolerance of the graminicide application were good. Additionally, pest pressure was not high, and, in particular, aphid populations were below the threshold level.

Another aspect to explore was soil nutrients — could Vaughn’s crop be suffering from a nutrient imbalance or deficiency? After looking at his records, I thought Vaughn had a good fertility plan, as he’d applied 60 pounds of MicroEssentials SZ (12-40-0-10S-1Zn) at seeding. Not to mention the symptoms were present in the majority of Vaughn’s lentil fields as well as most of the neighbouring lentil fields in the surrounding Assiniboia area. The problem was too widespread to be a nutrient or micronutrient issue.

Our investigation was narrowing. We’d eliminated several theories, leaving us to consider disease pressure and environmental stress. But which factor had caused the plant injury, and how would that be determined?

Crop Advisor’s Solution: Injured lentils: disease or environment?

Several severe rainstorms had passed through the area ten days earlier, bringing high amounts of moisture. These storms may have increased the crop’s susceptibility to disease, or the adverse environmental conditions could have put stress on the plants. Also, both disease pressure and environmental stress would injure lentil crops across a large area. We needed to sort out which factor was causing the leaf damage.

Symptoms exhibited in Vaughn’s lentil crop were similar to those found on stemphylium blight- infected plants. Stemphylium blight is common in lentils in this area, and can happen at any plant stage.

Lentils infected with the fungal pathogen that causes stemphylium blight present white- to cream-col- oured lesions, which spread across the entire leaf from the leaf tip in an angular direction.

Alternatively, plants affected by environmental stress, such as strong winds and heavy rain, could also turn yellow or white at the leaf tips and wilt. However, in order to prove the injury was caused by environmental stress, stemphylium blight had to be ruled out.

I sent plant samples from Vaughn’s and several other lentil fields in the area to the Crop Protection Laboratory in Regina, Sask., which determined the samples were negative for the disease.

That left one likely source of plant damage — environmental stress caused by wind and excess moisture. Laboratory test results confirmed the damage was characteristic of wind and rain damage, although the symptoms look similar to those stemphylium blight presents. In addition, the majority of affected fields in the Assiniboia area were located where the storms were most severe.

Wind damage can occur to crops at any plant stage, and the symptoms may appear similar to those caused by disease. It is important to test samples for confirmation of the symptoms’ cause, so a fungicide is not applied when it is not required.

In Vaughn’s case, the lentil plants grew out of the leaf damage and the yield at harvest was not affected.

Angie Berner, PAg, works for Richardson Pioneer Ltd. in Assiniboia, Sask.

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