Harvest is still several weeks away but a widespread infection of aster yellows could cut canola yields in parts of Manitoba by five to 10 percent.
Now that canola crops have moved past the bloom stage, it’s become apparent to canola growers, plant pathologists and crop advisers that the level of aster yellows is much worse than usual this summer in Manitoba.
Northwest of Minnedosa, for example, about 90 percent of canola fields have plants infected with aster yellows, said Elmer Kaskiw, Manitoba Agriculture crop production advisor in Shoal Lake, Man.
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“I’ve seen numerous fields, seen numerous (infected) plants and had numerous calls on it,” said Kaskiw.
Holly Derksen, Manitoba Agriculture plant pathologist, said canola growers are detecting aster yellows in fields across the province.
“The fields that I’ve been going into and rating for disease, it’s probably between five to 10 percent of plants are showing some level of aster yellows,” she said, from her office in Carman. “But it’s too early to tell what kind of yield loss that’s going to mean.”
While Derksen is holding out hope for yield, Kaskiw said growers may see yield losses of five to 10 percent.
At $15 per bushel, a 10 percent loss is a significant hit, he added.
“On a 40 bushel (per acre) canola crop, if you lose 10 percent, or four bushels at $15 (per bu.), you’re up at $60 (per acre).”
In Saskatchewan, Faye Dokken-Bouchard, a plant disease specialist with Saskatchewan Agriculture, said the province could see the largest incidence of aster yellows since 2007.
That year, two percent of fields were infected, although some fields saw 15 percent — and as much as 40 percent in smaller patches — with higher rates in northeastern Saskatchewan.
While she’s heard reports of those larger digits this year, the actual damage won’t be tallied until the disease survey is conducted in August.
“We’ll probably see it in most areas,” said Dokken-Bouchard.
In addition to canola, aster yellows has infected flax crops in Manitoba and will likely cause yield loss, Kaskiw said.
As early as April, entomologists in Manitoba alerted growers that an aster leafhopper outbreak was a possibility this year, because the insects were covering the landscape in Minnesota and South Dakota. It’s normally too cold on the Prairies for leafhoppers to overwinter, so timely southerly winds and the prevalence of leafhoppers south of the border can push the insects north to Manitoba.
When the leafhoppers did arrive this spring in large numbers, tests were done to determine the level of aster yellows phytoplasma in the insect population.
The results were not encouraging, said John Gavloski, Manitoba Agriculture entomologist.
Normally, three to five percent of aster leafhoppers carry the phytoplasma. This year, in some areas, 12 percent of leafhoppers were infected with the disease.
“In short, the phytoplasma infection levels were higher than normal in the aster leafhoppers,” Gavloski said.
Overall, it appears that aster yellows has done the most damage to canola seeded between May 1 and May 15, Derksen said — possibly, because the crop emerged when the aster leafhopper population hit its peak.
Faced with the possibility of a five to 10 percent yield loss, canola growers have told Gavloski that they intend to spray their fields with insecticide next year.
Unfortunately, applying insecticide to field crops for aster leafhoppers is pointless, Gavloski said.
Carrot growers in Manitoba spray their crops as often as once a week to control leafhoppers because aster yellows can deform the carrot’s shape and taint its taste.
Nonetheless, if a canola grower applies insecticide one time, leafhoppers will simply move in from an adjacent field or another generation of the insect will emerge.
So, a canola grower would have to spray multiple times to prevent aster yellows infection.
“When you look at the economics of it, it doesn’t pay,” Gavloski said. “This is one of those things, with field crops, there really isn’t anything you can do.”
What is aster yellows?
Aster yellows is a phytoplasma, or a plant pathogenic micro-organism. Transmitted by aster leafhoppers, it can infect canola, alfalfa, flax, sunflower, echinacea, caraway, coriander, carrot, pea, ornamental plants and weeds.
In canola, aster yellows deforms the pods and flowers of the oilseed plants. Infected plants take on a purple tinge and instead of pods, the plants form hollow, kidney shaped structures that are devoid of seeds.
Canola with aster yellows appears taller than the rest of the crop. Normal canola plants tend to lean one direction, because of the weight of the seeds. But canola infected with aster yellows stands upright, because there are no seeds to weigh the plant down.
In flax, instead of producing flowers the tops of plants produce additional leaves, which tend to turn yellow.
Source: Manitoba Agriculture and Agriculture Saskatchewan
