Some Answers but More Unanswered Questions About Aster Yellows

Aster yellows infection of canola. 2012. Photo credit: Tiffany Martinka, CCC

It’s the nasty phytoplasma that took many Prairie farmers by surprise in 2012 — aster yellows. Carried on the aster leafhopper, aster yellows can infect over 200 species but took a particularly heavy toll on canola this year. The irony is, canola isn’t even a preferred food source, as the leafhopper tends to prefer grasses. Still, some fields were hit with 25% and much higher infection, causing significant economic losses to an already struggling crop.

The kicker with aster yellows is that there really is no viable control option — it’s not a fungus so fungicides are useless against it, and the insects that carry it come up in waves with every south wind, so spraying isn’t cost effective. There are also very few cultural controls a farmer can implement to avoid or decrease infection.

Tiffany Martinka, agronomy specialist for eastern Saskatchewan with the Canola Council of Canada, outlines the few things farmers can do about aster yellows. Although the insects that carry the phytoplasma don’t typically overwinter, the phytoplasma itself does. The phytoplasma can over winter in the roots of perennial weeds and shrubs. This may explain why weedy fields seemed to show a higher incidence of infection. So cleaner fields may lead to lower incidence.

Martinka notes that this year was really unprecedented, and that the problem could have been even worse than we realize. “There were many plants that were testing positive for aster yellows but weren’t showing symptoms. For every one plant showing symptoms over twice as many were testing positive but with no visual symptoms.”

The small comfort in all this, if there is one, is that while there’s very little farmers can do to control the pest, it’s not often an issue. This year’s specific wind patterns are the likely culprit to the high levels and wide geographic area of infection. It’s unlikely farmers will be faced with the same levels next year.

The Canola Council of Canada recently compiled a frequently asked questions on the pest, including if there are specific canola types that the pest prefers. Click here to read more.


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