I don’t mean dull or uninteresting. I mean the types of bugs that burrow into your trees and cause damage. Every eco-system that has trees has some type of boring insect, usually the young stage of a beetle or weevil (Coleoptera). I don’t count termites in this group because, largely, they eat dead wood or lumber, not live trees. I’m sure Mother Nature considers the termite a good friend and an awesome recycler, breaking down fallen trees in the forest or jungle. Humans don’t appreciate them when they start to eat their way through the wooden infrastructure of our buildings, bridges and furniture.

Let’s look at our native poplar borer. The adults live for just a few months in early summer. They feed on tender new growth. The female will lay eggs in furrows in the bark. The eggs hatch and the babies burrow into the tree. They can live two to four years inside a tree! They eat xylem and phloem, disrupting the flow of water and nutrients through the tree. They can munch their way right through to the heartwood and seriously compromise a tree.

When diagnosing pests and diseases of trees and shrubs we’re looking for signs and symptoms. Signs that you have a pest include small holes in the trunk. In the case of poplar borer these are near the base or above the root flare, and may leak sap. There may be frass or sawdust at or under the hole. If woodpeckers are particularly interested in your trees you may have a boring insect. In the case of the bronze birch borer, the holes are a distinctive ‘D’ shape and are higher, usually between a human’s knee and shoulder. Symptoms of borers include die back of the top growth or side branches, swelling under the bark or sap leaking.

Generally, our native boring insects are not a huge problem. They are part of an eco-system, they have their good years and their bad years. They have their own predators, diseases and stresses. Late frost can kill the emerging adults. Woodpeckers and nematodes can attack them, they have their own parasites and fungal diseases. Research has shown that a healthy tree is less prone to borer attacks. Some years ago the paper birch (Betula) became very popular as a landscape tree here on the Prairies. Natively, the paper birch is found in moist areas along streams, lakes, boggy areas. Homeowners bought them, plunked them in the middle of a suburban lawn and ignored them. The trees were stressed, thirsty and were attacked by bronze birch borers. Keeping your trees healthy is half the battle; choosing the right tree is the other half.

Twenty years ago we had a class of pesticides known as systemics. These were chemicals that, to simplify, were absorbed by the woody plant, became part of the plant and bugs that ate that plant died. It was really the only way to deal with pests protected by being inside the tree. Most systemics were removed from sale to residential users in Canada for being too toxic to humans, to the birds and the bees, and to aquatic creatures. Anyone remember Cygon 2-E? I am watching, with interest, the Canadian Forest Service developing a systemic from the Neem tree called TreeAzin.

When boring insects become a huge problem is when they are not native. They have no predators, no diseases and trees do not have a natural resistance. A recent example of a disastrous introduction is the accidental importation of the Emerald Ash Borer into North America. In it’s native Siberia, northern Russia and north Asia the beetle have predators such as parasitizing wasps. Native birds will eat the adults, but here the birds didn’t know what to make of them. The loss in mature ash trees is estimated in millions of trees and billions of dollars. Read more about it here. Another case is the disease Dutch Elm Disease, when a the Elm Bark Beetle was introduced. The beetles carried a fungus which devastated the majestic elms. Read more about it here. The loss of millions of shade trees results in loss of habitat, loss of shade and cooling, loss of windbreak.

So what’s the homeowner to do? First and foremost, keep your trees healthy. Fertilize or amend your soil in spring, water well during times of drought. Examine your trees in Spring and Fall looking for signs and symptoms. Check the websites of your local extension service, local university or government body responsible for forests and agriculture (in Canada to Natural Resources Canada) to stay apprised of problems. Because isn’t your glorious shade tree worth a little effort?