At nearly every field day for the past few years in Saskatchewan, the presenting agronomist would hold up a mangled canola head and ask, “Can anyone tell me what this is?” Most farmers would look closer, but few had an answer. Being from Manitoba, I’d pipe up, “Aster yellows.” Aster yellows is relatively common in Manitoba, though at very low levels most years, and once you see the distinctive deformed head it causes, its easy to spot in subsequent years. Typically, the overall impact to yield is low. But this year has been anything but typical.
First, some background. Aster yellows is not a fungus. It’s a phytoplasma, a bacteria-like pest, carried by a particular insect (the aster leafhopper) that is swooped up on wind currents from the south and unceremoniously dropped down on farmers’ fields across the Prairies. There is no treatment and no real means of avoidance (unless you can figure out a way to control the wind. In which case, focus on bigger things than aster yellows, please).
Unfortunately for many in Saskatchewan and parts of Manitoba, this year has seen a particularly devastating infection of aster yellows on not just canola, but several other crop types. It’s not unheard of for a quarter or part of quarter to be severely infested — it’s just the luck of the draw — but the jury is still out on why this year is so bad. The air currents and drought conditions in the U.S. likely played a role, but some farmers have reported that fields that didn’t receive a pre-seed burn-off fared far worse. What’s more, reports of immature canola sprouting in the pod has been blamed on aster yellows as well, but that’s more likely because of hot, dry conditions than aster yellows.
What many farmers and agronomists have learned this year is that there are many things we still don’t understand about aster yellows. Would spraying the phytoplasma-carrying insect help? Why do “dirty” fields show higher levels of damage? Is there a way to anticipate which fields may be susceptible or when the insects may arrive? In all likelihood, however, this year is an anomaly and it could be many, many years before we see levels like this again.
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