Seeing lots of bugs on your cottage trees this summer? That’s not necessarily bad news. But a select few unwanted guests can quietly destroy your leafy pals from the inside out. From leaf-chomping caterpillars to wood-boring beetles, catching destructive insects early is key to saving your canopy.
Not all “pests” are harmful, says Ryan Statham, an arborist with Davey Tree in Strathroy, Ont. Even if they might look like pests to you. Pollinators such as bees and butterflies—plus moths, ants, and flies—are all examples of helpful insects that are key to the growth of new plants. Most of these insects also pose little threat to plant and tree species. Then there are the “not helpful, but usually not harmful” insects such as aphids (tiny green sap-sucking bugs found on most trees). They’re harmless in small numbers, says Statham, but in large numbers, they can damage leaves, twigs, and roots, and cause mould and diseases to spread.
A good rule of thumb to maintain healthy trees is to plant a wide variety of native species for better resilience against diseases and pest infestations, says Statham. Making sure trees are receiving enough water and fertilizer will also help them to be more resilient. But most of all, know how to recognize when harmful pests have made their way into your yard and when to enlist an arborist for help. Here are Statham’s expert insights into the top tree pests to be aware of this summer.
Spongy moths
Spongy moths (formerly known as European gypsy moths) are an invasive species that defoliate hardwood trees in massive quantities. During population booms—about every five to seven years—masses of these moths, in their caterpillar stage, can be seen “marching up the trunks” of broadleaf and conifer trees, says Statham. Egg masses can be found on tree bark or nearby rocks and have a fuzzy tan appearance. In their caterpillar stage, spongy moths are dark and fuzzy with blue and red dots; at the adult stage, they bear brownish-grey wings with wavy patterns. Statham says you can prevent an infestation on your property by destroying the eggs (which look like little sponges) in fall and winter and putting a sticky substance, such as tape, around the trunk of the tree to ward off the caterpillars.
Cottage Q&A: What’s wrong with this beech tree?
Emerald ash borers
These borers are another invasive species (they’re native to Asia). “The beetle itself is actually pretty gorgeous,” says Statham. “They’re a bright emerald colour and about the size of your pinky nail.” As adult beetles, emerald ash borers are mostly harmless, he says. But during their larval stage they feed underneath the bark of ash trees on the soft inner tissue (called cambium). “When you have thousands of them on one tree, it really starts to impact the health of the plant, because it’s cutting off all those conductive tissues,” says Statham. “It essentially chokes the tree off, disconnecting the crown from the root system.” The most obvious signs of infestation are rapid canopy dieback starting at the top, along with D-shaped exit holes created by the larvae emerging when they hatch. Statham says chemical trunk injections done by arborists are the best way to get rid of this pest.
Forest tent caterpillars
Despite their name, forest tent caterpillars don’t make tents, but rather spin silken mats which can be found on tree trunks of many deciduous trees across Canada. Their MO is defoliating host trees while feeding, which decreases the photosynthesis capabilities of the tree, weakening it over time, especially if multiple outbreaks occur alongside droughts. Statham says that while they can be pesky, they’re relatively easy to remove. “You simply have to cut out their nests from the tree,” he says.
Cottage Q&A: What is this strange tree growth?
Magnolia scale
“We see this type of scale pretty often this time of year,” says Statham. It’s the largest soft scale insect in North America and it targets magnolia trees—such as Canada’s native cucumber tree—by feeding on the sap and excreting a sticky waste product called honeydew, which falls and causes a black fungus called sooty mould to grow at the base of the tree. The honeydew is also very sweet, says Statham, so it attracts wasps, flies, and other bothersome insects. You’ll know your tree has a scale infection if you see large, whitish, waxy looking bumps on your tree, which are what the insect hides under. “Scale insects are kind of insidious because they’re like a turtle,” says Statham. “They’re underneath this scale covering, which makes them difficult to treat.”
Related Story Meet 7 early risers of the wildlife world
Related Story Ew! This is why some plants stink when they bloom
Related Story Why moths are the unsung, nighttime pollinators of cottage country