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Via EnjoyGardening)
Posted by admin to Current Articles on 2008-02-01, 07:07:34
first published January 24, 2008
Poplars and prairies—it’s hard to think of one without the other. Over the last century, poplars have been planted in vast numbers across the prairies and, for the most part, it’s because they were a practical choice for our climate. My family alone planted hundreds on our farm to create hardy shelterbelts that would grow quickly and endure extremely cold and windy winters. And even though poplars have long been thought of as weedy and out of style, they continue to be planted because their resilience and toughness trump their questionable beauty—or that is, they used to.
If nature has its way, the resilience of poplars might be put to the test in next few years. A new and potentially serious poplar disease that’s indigenous to Eastern Canada has shown up in Manitoba and could threaten a wide variety of poplar species in both Saskatchewan and Alberta. It is called Bronze Leaf Disease (BLD), and it’s caused by a fungus called Apioplagiostoma populi. The fungi’s hallmark, as the disease’s name implies, is that it rapidly transforms poplar leaves from a healthy green to a sickly bronze.
April showers make leaves cower
The life cycle of BLD looks something like this. Showery, mild weather (18C or so) during mid to late spring causes the fungi to produce spores that are then dispersed to poplar leaves via the wind and rain. By midsummer, infected leaves turn a reddish or orangey brown around their edges, and by late summer, the disease renders the leaves completely brown. The remainder of the cycle is just as straightforward. Throughout the winter, infected leaves tend to cling to the branches and come spring, the disease resumes its dastardly work. Sounds like a reasonable enough disease, right? Umm, no. If BLD had the decency to restrict itself to staying in the leaves, it would be, but unfortunately, it frequently has the audacity to move into the branches, causing sensitive species of poplar to die within a few years of infection.
Now, I don’t want to create a panic. After all, BLD is but one of many diseases we must contend with. However, it is one we really should keep an eye on—the most compelling reason being that the dominant species of broadleaf trees in our boreal forest are poplars, which means that BLD has the potential to cause serious damage to the forestry industry. Add the fact that Swedish columnar aspen and ‘Tower’ are two of the most popular poplar varieties for landscaping and you get what seems like a reasonable cause for concern.
Constant cleanup
There are no registered chemical controls for BLD and none on the horizon. So the best way to keep it out is to slam the door on it, which, practically speaking, means all poplars should be bought from reputable suppliers who check to make sure their trees are disease free. As for the existing trees in your yard, be sure to give them a once-over. If a poplar does look like it might be infected, zip-lock a leaf sample in a bag and take it to a garden centre that has trained staff capable of assessing the problem. If it is BLD, keep the disease under control by removing infected leaves during the summer and raking them up during fall cleanup. Removal of dead branches and pruning to thin the tree canopy (thereby increasing air movement) will also help. Of course, pruning millions of hectares of boreal forest is neither practical nor cost effective, but what we can do is monitor the problem. And that’s exactly what the provincial governments across the prairies are doing. To date, with the exception of Manitoba, there is only scattered anecdotal evidence of BLD showing up here.
That’s BLD in a nutshell: audacious, a lot to clean up after, but not out-maneuverable. In fact, when it comes to combating BLD, the saving grace for poplars might just be their reputation for being a weedy species. After all, in my 30 years in the horticultural business, I’ve never heard of any disease that could eradicate a weed—and I’ve looked…trust me on that.
