Crop Advisor’s Casebook: The case of the bronzing lentils

A Crop Advisor’s Solution from the July 22, 2014 issue of Grainews

Rob, a mixed grain and cattle farmer east of Swift Current, Sask., went on a week-long fishing trip in mid-July. Upon returning to his 3,000-acre farm where he grows canola, lentils, durum and barley, Rob noticed the plants in one of his lentil fields were turning brown and appeared to be dying. He called me immediately.

“I’m not sure what’s wrong with that lentil field,” Rob said. “All my other fields of lentils look as healthy as can be. And we sprayed all of our lentils for disease just before I left for my trip.”

Jeneen Ewen

Jeneen Ewen
photo: Supplied

When I drove out to visit, Rob took me to look at the affected field, which was relatively flat with a couple of low spots. Right away, I could see bronzing of the leaves and dead-looking plants in some areas of the lentil crop. Some plants in the low spots were already starting to lose their leaves, even though the stems were still green.

In general, the lentils were very bushy with a lot of plant material present. A closer look at the most severely affected plants revealed that some of them didn’t have many pods. The leaves of affected plants had small lesions that were light brown in colour, although we couldn’t spot any lesions or wounds on the stems. We pulled up a few plants to examine the roots and they looked healthy, with good nodulation.

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The bronzing within the crop wasn’t occurring just in the low areas, but was happening on slopes and in higher areas of the field as well. According to Rob, the affected areas seemed to be spreading, getting larger and larger every day.

My immediate thought was that it could be ascochyta or anthracnose, both common lentil diseases. I knew a few farmers in the area had been spraying for both diseases, but I couldn’t see physical evidence of either ascochyta or anthracnose on these lentil plants and Rob had indicated he’d already sprayed the crop for both diseases.

My second thought was that perhaps the lentils in the low areas of the field were suffering from the effects of recent heavy rainfalls. However, the symptoms weren’t just isolated to plants in low spots — they were all over the field. There had to be an explanation, but what?

Crop Advisor’s Solution: Stemphylium

In late July I got a call from Rob, a mixed grain and cattle farmer east of Swift Current, Sask. He had just returned home from a weeklong fishing trip and noticed the leaves of plants in one of his lentil fields had small lesions and were turning brown, although the stems were still green and appeared undamaged and the roots healthy. It was only one field that was affected — the others were fine.

I paid Rob a visit, and when he showed me the affected field I could see bronzing occurring throughout the crop. In addition to turning brown, the lentil plants were losing their leaves and many appeared to be dying.

I immediately suspected it to be one of the two most common lentil diseases, ascochyta or anthracnose. However, Rob had sprayed for these, and the plants didn’t show the typical signs that I’d expect to see from these diseases.

I thought the lentils in the low spots of the field were possibly dying because of standing water from recent heavy rainfalls, but the affected plants were all over the field, not just in low-lying areas.

I asked Rob to tell me a little more about the history of the affected field. It turned out there was one major difference between this lentil field and the others on Rob’s 3,000-acre farm, which also included canola, durum and barley — this field had lentils on it only two years previously, while his other lentil fields were on a four-year rotation. This confirmed my suspicion that it had to be a disease issue.

I sent a few plants to the crop protection lab in Regina to get an accurate disease diagnosis. Stemphylium blight was confirmed. This fungal disease is on the rise in Saskatchewan and can occur when there is a heavy rain during the mid-to-late podding stage. Little is known about the disease, which is caused by the Stemphylium botryosum fungus. It thrives when lentil leaves are wet for at least eight hours, temperatures hit 25 degrees and humidity is hovering around the 85 per cent mark.

There wasn’t much Rob could do at this point. There is no fungicide yet registered for stemphylium blight in Canada. The lentil yield in that field was lower compared to his other fields, but not significantly — Rob was happy with what he got.

I told Rob that all he could really do in future was to watch his fields for signs of stemphylium blight, and maintain proper crop rotations to help manage all lentil diseases. Until further research reveals more about stemphylium blight and a fungicide becomes available to prevent it, a watchful eye is Rob’s best defense against this particular disease.

Jeneen Ewen is a sales agronomist with Richardson Pioneer Ltd. in Reed Lake, Sask.

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