Clubroot
If you are a prairie gardener who grows cabbage, cauliflower, broccoli or any other member of the crucifer family, you’ll want to be extra cautious about adding topsoil to your yard next year. A potentially devastating disease called clubroot has found its way into many of the soils in central Alberta and has the potential to spread across the prairies, causing damage to our crops, wallets and, in some cases, livelihoods.
So what the heck is clubroot, you ask. Well, it’s a soil-borne disease that’s transferred from field to field by means of contaminated soil or infected plant parts. The causal organism is Plasmodiophora brassicae, and once it gets into the soil, it waits patiently until it senses a certain chemical secretion from the roots of cruciferous plants. That chemical signal then triggers the clubroot organism to morph into structures that swim toward the developing plants and penetrate the roots. Once inside, the clubroot organism rapidly reproduces and transforms healthy, white, fibrous roots into gnarled, black and dysfunctional clubby masses. Not surprisingly, the infected plants die outright or are severely weakened.
Clubroot has shown up briefly on the prairies before but, up until recently, never became established. Unfortunately though, the clubroot organism that’s recently taken up residence shows no signs of vacating Alberta any time soon. In fact, it seems to be spreading at an alarming rate. At last count, it had become established in 10 counties in central Alberta and 1 county in southern Alberta.
How clubroot took root in all these counties is a bit of mystery and one that plays out a bit like an episode from CSI. When I spoke to Dr. Stephen Strelkov, a plant pathologist from the University of Alberta and expert on clubroot, he said the theory about the disease’s origin is still somewhat speculative but it’s thought that the infestation likely originated with infected plant material and soil from a vegetable garden that was presumably dumped onto a canola field outside of Edmonton. From that single field, clubroot probably hitched a ride on some soil that clung to a piece of farm equipment and then made its way to another patch of land.
Interesting?—yes—but if you’re a home gardener who doesn’t grow susceptible vegetables, why should you care about clubroot’s spread? Well, in a strange twist of fate, this strain of clubroot has done something that’s sent a chill through the agricultural community—it’s expanded its repertoire of food choices and acquired an appetite for the Cinderella crop of the prairies: canola.
Canola is a member of the crucifer family, but up until this local strain of clubroot came on the scene, was relatively safe from attack. Now every canola crop is potentially threatened. If that’s still not enough to pique your attention, think of the financial ramifications. According to the Canola Council of Canada’s website, this country’s canola industry adds over $11 billion to our economy, and that doesn’t even include canola’s newest use as a source of biodiesel fuels.
More bad news
There’s no cure and little in the way of control for clubroot. If that’s not grim enough, once it gets into the soil, it can survive for at least 20 years. And guess, dear gardeners, where the topsoil we add to our yards comes from? Yup. So if you buy topsoil that hasn’t been tested, you run the risk of inadvertently introducing it into your soil. And there’s the rub: testing for clubroot is currently not a requirement for being able to sell topsoil. According to Dr. Strelkov, there are local labs that can test for the disease’s presence, so the capability is there. I for one just hope that the topsoil companies will put the onus on themselves to provide lab reports that show that their product is clubroot free.
Any new discovery about a potentially threatening disease is always overwhelming to hear about, but as in the case of most things, knowledge is power. The good news is that finding out about clubroot in the early stages means it doesn’t have to become unmanageable. But the fact that clubroot was smart enough to invade canola is reason enough for everyone—gardener or otherwise—to pay close attention and be proactive. After all, there’s a famous poet who once said, “Nature is not a place to visit, it is home.”
