John, a producer who grows wheat, canola, peas and lentils on his 5,000-acre grain farm just west of Swift Current, Sask., was out spraying peas in mid-June when he spotted a problem with another one of his crops just across the road. The wheat in that field looked like it was dying off.
Not long after that I got a distress call from John, who couldn’t believe what he was seeing. “We just scouted this field last week, and now my crop is brown and dying!”
I had been to this wheat field just a week before, and while we saw some plants that appeared wind whipped from a recent windstorm, there were no signs of the kind of damage John was describing on the phone. I assured him I’d be right out to have a look.
When I arrived at John’s wheat field, I could see the crop looked far from healthy. The wheat plants were stunted and yellow-green in colour, with older leaves that were brown and starting to die off. Newer growth was starting to show the same symptoms. A closer examination of a damaged plant revealed small, dark lesions with tan-coloured halos that appeared to be growing in size.
Right away, I thought disease might be the culprit, but I was at a loss to explain what could be causing this kind of damage at such an aggressive pace. I didn’t think this was the work of insects, as there were no signs of feeding, and John hadn’t applied any chemicals in the field within the last week.
When I asked his crop rotation, John told me he alternated canola and pulse crops with the wheat in this field. He had a good fertility program, applying fertilizer with the seed and subsequently through mid-row banding applications. I also inquired about the weather, and John said it had been unusually wet and warm for the past week.
While walking through the field, I spotted something unusual — a 20-acre patch where the plants were dark green and much healthier looking. John informed me that was where a fire the previous fall had burned 20 acres of stubble just after harvest. It was this discovery that enabled me to zero in on the source of the problem.
Crop Advisor’s Solution: Tan spot causes sickly looking wheat
Initially, I suspected that tan spot was to blame; however, I hadn’t seen any signs of this fungal disease when John and I had scouted the same field just a week previously, and I didn’t know what could be causing this kind of damage to happen so fast.
I found my answer when I came across a 20-acre patch in the middle of the field, where the plants were dark green and much healthier looking. This was where a fire the previous fall had burned 20 acres of stubble just after harvest.
This indicated tan spot had been present in the field in plant residue, possibly from the last time he’d planted wheat there, with the exception of the area where the stubble had been burned away. Recent warm, wet weather, coupled with the wheat plants being injured from a wind whipping they sustained the week before, had contributed to the aggressive outbreak of the disease.
Fortunately for John, there was enough time left in the season to combat the tan spot problem. I recommended that he add a fungicide to his in-crop herbicide application to help get the disease under control. The field started coming back and, following a second fungicide application at the flag leaf stage, the wheat crop rebounded to the point where there was no loss of yield.
While John didn’t lose his wheat crop, he did gain a valuable lesson about the importance of scouting and keeping vigilant. Fungal diseases like tan spot can proliferate very quickly if the conditions are right, so it’s important to keep an eye on crops throughout the season. In John’s case, he’d be wise to also pay close attention to crop rotations and field history so that the proper precautions for disease prevention can be carried out.
Jeneen Burnett is a regional sales agronomist with Richardson Pioneer Ltd. at Reed Lake, Sask.