Aphids like to feed on the soft growth of almost any plant. This includes most trees, though in Calgary Birch (Betula), Willow (Salix), Maple (Acer) and Mayday (Prunus padus) seem to be most affected. Aphids are able to reproduce without males which can lead to huge populations some years. Heavy populations can be tough to control as there are many stages of insect present at any given time and some stages may be less susceptible to chemical control. Aphids are a pear shaped insect that are usually green or black but can also be yellow, grey, black, brown or pink. They suck the sap from leaves and stems. The aphid digests a few nutrients from the sap and the rest is excreted as “honeydew,” (a clear, sticky substance) which makes leaves on affected trees and anything underneath appear shiny. Fungus (Sooty Mold) then grows on the honeydew, creating an objectionable mess that can stick to vehicles, decks, buildings and walkways underneath the affected trees. This mess can be washed off with soap and water.

Tree Damage

  • Aphids pierce and suck out the contents of leaves and soft stems of trees and other plants.
  • The resulting excrement is referred to as “honeydew” and sticks to the leaves and if there is a large infestation, honeydew will usually be found on items under the tree as well like vehicles, patio furniture, and sidewalks.
  • Damage to trees is limited and minor infestations may warrant no action.

Control Measures

Aphids are found everywhere and are virtually impossible eliminate. They can, however, be kept under control.

  • Keep an eye out for signs of an infestation so controls can be started early.
  • Wash aphids off the tree with a strong spray of water or use insecticidal soap (be sure to follow label directions).
  • A professional pesticide applicator will have equipment capable of reaching taller trees with high pressure water to help dislodge the insect.
  • Ants and Wasps protect or “farm” aphids so they can feed off the honeydew. Eliminating the ants will allow predators of the aphids to help control populations.
  • Healthy trees are better able to withstand infestation of any insect.