Damage in wheat also seen | Extent of devastation across Prairies alarming agronomists
Tiny pests are causing massive damage to this year’s bountiful crops.
Aster yellows disease was brought north from the U.S. Midwest on the bodies of the six-spotted leafhopper, a white insect the size of an aphid.
“We’ve lost hundreds of millions of dollars to aster yellows,” said Ieuan Evans, a forensic pathologist with Agri-Trend Agrology Ltd.
“I’ve lived in the Prairies for 40 years and this is the worst I’ve ever seen (aster yellows) and the most widespread I’ve ever seen it.”
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Drought in the U.S. Midwest forced hundreds of billions of leafhoppers to migrate to Western Canada in search of food. They rose in columns thousands of feet into the air and drifted north on the winds.
“(When) they hit a cold front below 15 C, they drop to the ground like confetti at a wedding,” said Evans.
The leafhoppers descended on fields throughout Western Canada one month earlier than usual in mid-May, infecting cereal and oilseed plants at the vulnerable seedling stage of development.
Three to five percent of the hoppers usually carry aster yellows disease, but tests showed the rate of infection with the phytoplasma, which is similar to a virus, was as high as 12 percent this year for some unknown reason.
That has resulted in infection rates from trace amounts to 40 percent in canola crops in all three prairie provinces.
“I would stick my neck out and say the average for the Prairies may be as much as 10 percent,” said Evans.
Statistics Canada is estimating a 16 million tonne canola crop, which means a potential yield loss of 1.6 million tonnes. At today’s prices of about $630 per tonne, that’s a $1 billion loss in canola alone.
But what stunned Evans is that the damage is every bit as extensive in wheat. The disease has caused yellowish to reddish foliage in wheat fields along with the death of randomly scattered plants at the early milk stage of development.
He said he was floored by the extreme damage to wheat fields near Swan River, Man., northeastern Saskatchewan and central and northern Alberta, where there are fields with 30 to 40 percent bleached or dying wheat heads.
Growers mistakenly believe it is root rot. Agri-Trend has confirmed in lab tests that it is indeed aster yellows damage.
“Across the Prairies, I would be as bold to say that between seven and 10 percent of the wheat crop has been lost to aster yellows,” he said.
Evans expects to find similar damage in barley and flax fields, but hasn’t tested those crops yet.
Holly Derksen, field crop pathologist with Manitoba Agriculture, thinks it is premature to be assigning a level of destruction to the disease.
“There will definitely be yield loss from aster yellows, I just don’t know what it’s going to look like,” she said.
However, she agreed with Evans that the damage will extend beyond canola into the cereal crops.
“Most (producers) aren’t recognizing it for what it is,” she said. “I can see it in most crops I come across.”
Evans said there is nothing growers can do about the disease this year, but they’ve learned a lesson and should be prepared to spray their crops in the future when the leafhopper hordes arrive this early.
Derksen isn’t convinced spraying is a good idea, even in a year like this.
“I don’t think it’s at an economic level where it would have paid to spray because to go in and control them you have to make repeated applications of the chemical,” she said.
Fortunately only a small portion of leafhoppers overwinter in Canada, so the aster yellows problem should disappear as fast as it arrived.
“We’re hoping that this is just a rare year,” said Derksen.
