Caterpillar outbreak's impact on Calgary trees primarily cosmetic (for now)
An unexpected leafroller caterpillar infestation in Calgary and surrounding communities has left aspen trees with curled leaves covered in bite marks but arborists predict the damage will be short-lived.
“We’re seeing quite an infestation of caterpillars, more than we usually see in the spring,” said Codie Anderson, a board certified master arborist and ArborCare Tree Service manager. “It’s not uncommon to have the occasional outbreak but this type of citywide, or even beyond the city, is really quite heavy, quite unusual.”
“We were expecting a lighter year for insects after the winter that we had but then spring was beautiful, it was the perfect conditions for all the plants to catch up and for all the insects to catch up and they’ve really done it.”
Anderson says leafroller caterpillars turn leaves into makeshift cocoons where they pupate and become moths. “It keeps them pretty safe from most things. Even the sprays, once you get to the stage where everything’s rolled up, are less effective.”
The caterpillars are doing significant damage to native aspen stands in the wild this year but the damaged leaves that fall to the ground are beneficial and promote future growth. Homeowners may be disappointed by the cosmetic damage to their aspen trees but Anderson expects the trees will fully recover in the coming years assuming the cyclical nature of caterpillar infestations returns.
“In the residential landscape, it will range from a few rolled up leaves to all of the leaves gone off of your trees,” explained Anderson. “We can hope that this is a one off, we have this outbreak and it goes away. If it’s happening year after year, we can forecast a problem for the aspen stands. Predispose them to other insects, to diseases and just general decline.”
Anderson says there are steps homeowners can take to minimize the damage of caterpillars.
“Your best time to act is sooner than now, in fact before the leaves come out. A spray with a horticultural oil will take care of the eggs which have been laid on the branch in the fall. If you missed that window, you have a short time when the leaves come out to catch them with a spray. There are various things you can use. The best ones are biological, not gonna hurt mammals or birds. The caterpillar eats the leaf, that’s the end of the caterpillar.”
The leafrollers are not expected to inflict much more damage on the aspens in the Calgary-area this year. “We’re almost at the end of the season” said Anderson. “They’re done with what they’re going to do and will move on and become a moth, live out the cycle and lay more eggs and start again next year.”
Anderson says the heavy presence of leafrollers in 2018 will likely result in ‘an awful lot of eggs next year’ but ‘a good spring frost next year could be the end of them’.
With files from CTV's Bill Macfarlane