Hi! I live in Toronto’s West end (near-ish to High Park). We have three trembling aspens in our front yard that get infested with aphids that drop their sticky goo like rain on the car parked in the driveway, any car parked in front of the house and also coating all of the plants in the garden. The sticky honeydew is difficult to remove and attracts wasps which concerns us with a family member with an wasp allergy. We don’t want to use harmful pesticides and it is also difficult to apply anything high into the trees. Our neighbours aren’t loving us either!
Your poor trees! So lovely but so sticky….
Honeydew is the waste product aphids excrete, and attracts ants, wasps, flies and bees — most of which are certainly not welcome.
A few issues to consider:
- Ants are good friends of aphids – they ward off aphid predators to make sure that their supply of honeydew continues. Watch for ants and get rid of them (beware of ant traps that contain chemicals that children and animals might get into by mistake)
- Monitor your trees closely starting early in the growing season – at least a couple of times a week – so that you identify infestations early.
- Aphids thrive when there’s lots of nitrogen around – use slow-release fertilizers that don’t release high concentrations of nitrogen concentrations.
- Early in the season, if you see aphids, try spraying them off the trees with a strong spray of water. Once dislodged, most won’t be able to get back on the trees.
- Use an insecticidal soap to control the aphids – this is time-intensive as these liquids need to directly contact the aphids in order to be effective. Spray the tree until it’s dripping. It may take a few applications to get rid of the aphids. Insecticidal soaps are low in toxicity and don’t harm animals or beneficial insects (like bees and other pollinators).
- Dormant oil (also called horticultural oil) can be used to suffocate the aphids – this must be sprayed directly on the bugs, and can also kill other (beneficial) insects. If applied early in spring, oils will also kill off eggs of aphids that have overwintered.
Here are some helpful resources:
- Colorado State University’s Aphids on shade trees and ornamentals
- University of California’s IPM Aphids
- The Spruce Horticultural oil .
You may want to consult an arborist as to the best way to reach aphids high in the trees. Landscape Ontario provides a list of arborists in your area. As well, someone at your local nursery may have some suggestions – aphids are not uncommon.
All the best in controlling the aphids in your lovely aspens and winning back the affection of your neighbours!