Insects are one of the largest divisions of the animal kingdom. Though most species of insect do not cause harm to trees, some can be quite the pest! It is important to be able to recognize which kinds of insects are causing problems in order to choose the appropriate control measures to mitigate further damage.
Caterpillars and other leaf rollers
There may be a number of different insects attacking aspen trees in the County this year. The two main ones are aspen leaf rollers and speckled green fruit worm. There are also small numbers of large aspen tortrix and linden loopers, among others.
- One insecticide that can be used on the caterpillars is Bacillus thuringiensis (Bt). It would need to be applied in May while the larvae are still small.
- Any registered contact insecticide, like Malathion, can be used to help control these caterpillars on ornamental trees.
- Control of these caterpillars is usually not necessary due to the short duration of the outbreaks as there are a number of natural predators that keep the numbers in check.
- A large species of Ground Beetle is also present, commonly called the Fiery Hunter, that feeds on caterpillars. Avoid insecticides as they may harm these beneficial beetles.
Poplar borers live in aspens, cottonwoods, willows and poplars. They are often found in columnar poplars, around the edge of native aspen stands and lone trees. Noticeable signs include large bore holes with sawdust (shredded wood) coming out of the holes and piled at the base of the trunk. Sap leaks down and stains the bark brown attracting other insects. Trees can be weakened structurally when several larvae are present.
If a tree is infested, remove it and destroy the wood by chipping, burning or take it to a recycling centre. Many larvae are killed by woodpeckers, nematodes and other natural predators and over 60 per cent never make it to maturity.
Aphids live in many tree and plant species. Signs of them include honeydew falling from trees, curled and deformed leaves and shoots, and the presence of ants. There will be darkening of the bark on younger elms caused by sooty mould growing in the honeydew.
Spray aphids of a plant with a powerful stream of water. There are also many natural predators of aphids including ladybugs.
Visit Natural Resources Canada for more information on aphids.
Yellow-headed spruce sawfly
These can be found in a variety of spruce species, where you may notice larvae and defoliation of the ends of branches. Sawfly larvae can defoliate a tree if it is heavily infested. Bare branches and defoliation affect the aesthetics of a tree. Repeated defoliation is where the danger to the tree lies.
You can remove by hand or spray larvae off with high-pressure water. Disturbing the ground under the tree may disrupt pupation. There are also a lot of natural predators that will eat the pupating Sawfly, including birds and ground beetles.
Visit Natural Resources Canada for more information on yellow-headed spruce sawfly.
Ash leaf cone roller
These caterpillars live in green, manchurian and black ash trees.
Let nature take its course. This insect does not damage the leaf enough for it not to be able to perform photosynthesis. There are naturally occurring predators of this caterpillar, including a non-stinging wasp, birds and more.
Natural Resources Canada provides information on the following tree pests:
- Yellow-bellied sapsucker
- Dutch elm disease
- Spruce spider mite
- Bronze birch borer
- Fire blight
- Spruce needle rusts