Plenty of leaves are falling from trees these days, but those that stay on poplars and aspens might be signs of disease.
Bronze leaf disease was found in about 2005 in Manitoba and is slowly making its way westward. It affects aspen and poplar hybrids and can kill trees within three to five years if left unchecked.
Robert Spencer, a commercial horticulture specialist with Alberta Agriculture, said symptoms of the disease are much easier to spot in summer and fall.
It is characterized by a sudden change in colour of a branch or part of a branch. As the disease name suggests, infected parts of the tree turn a reddish bronze colour.
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Leaf veins and the tissues around the veins will remain green, as will the leaf stem, but the rest of the leaf colour will change, he said.
“The tricky part is, with some of these hybrids, the new growth can be quite red, and also a stress response can be a red colour. But the green veins are a fairly distinctive symptom,” Spencer said.
Infected leaves will often remain on the tree over the winter, possibly because the disease interferes with normal dormancy that induces leaf drop.
Pruning infected areas is the only known way to manage the disease. As well, monocultures of aspen or poplar should be avoided.
“That can cut down on the potential rate of spread, and anything we can do to keep the plants healthy and in good growing conditions will contribute to their health.”
The disease has been found in most major urban prairie centres, said Spencer. There is concern about potential spread to native stands of trembling aspen, although the risk level is unknown.
However, risk of disease shouldn’t discourage people from planting aspens and poplars.
Spencer said trees get sick all the time. It’s a matter of being observant and prepared to take action if problems arise.
“People often just plant them and ignore them. They take them for granted. Pay attention if something abnormal happens,” he advised.
“If you were thinking of planting a single species, maybe reconsider that, or look at alternatives or spread things out.”
