When I got a call from Bob in early July, informing me that his durum wheat heads were drying up and failing to properly fill, I thought the problem would be relatively easy to identify.
Bob, who farms 7,000 acres of canola, durum wheat and peas near Lampman, Sask., told me that his durum heads were drying out and failing to properly fill. The dried-out heads were scattered randomly across his fields, on both high and low ground, and the tillers were not fully emerging from the shoots.
Bob and I went through all possible causes for the symptoms. Almost immediately we ruled out a lack of moisture as the problem — although we’d had several weeks of dry, hot weather with sporadic rain on some fields, the drying heads were also appearing on the fields that had received enough rain. We also considered compaction along the headlands as a possible cause, as the spring had been so wet. But again, the symptoms were spread throughout the field.
“Did you plant certified seed? Was it treated?” I asked Bob. Although he had planted various types of seed — some treated, some untreated — there was little or no visual difference between the treated and untreated plants. And when we looked at fertility as a possible cause, we came up with nothing. Bob had supplied above-adequate nutrients to the field — added to which, the field had lain fallow in 2011 due to wet conditions. The problem now looked more complex than I’d initially thought.
But something had triggered in my mind when I saw how sporadically the dried-out heads were scattered through the field. Could it be a sporadic disease causing the problem? I posed this question to my colleagues. The answer was surprising!
Strange disease symptoms had also been found in canola this year. The cause of these symptoms in canola: aster yellows. The idea of the symptoms observed in Bob’s field being caused by aster yellows was kicked around the office. But did aster yellows affect cereal crops? I did some research and learned that it can — and the symptoms fit our hypothesis. We sent some samples away to be DNA tested for aster yellows phytoplasma. Sure enough, we’d found the culprit.
As it was a bad year for aster yellows, there wasn’t much Bob could do to manage the problem. There were more leafhoppers present this year than an average year, causing the disease they carry to be more prevalent. Because aster yellows is caused by a microorganism called phytoplasma, not a fungus, common fungicides would not prevent this disease.
We thought that the previous year’s warm winter had possibly allowed more leafhoppers, which carry aster yellows, to survive. Alternatively, the drought in the United States might have pushed the insect further north to find lush crops.
Bob lost some yield, but that harsh reality was softened by the understanding that he hadn’t done anything wrong — and there was nothing he could do to correct the problem. While we tossed around the possibility that spraying insecticide to kill the leafhoppers might limit the spread of aster yellows, we weren’t certain it would make the most economic sense.
“Chalk another one up to Mother Nature,” I said. “We just have to take the results we are given from year to year and learn from them, and hopefully limit damage in the future.” †