Integrated Pest Management

Tree Pest Problems

• Introduction
• Policy
• Lawns and Boulevards
• Trees
• Problem Weeds
• Mushrooms

Pests

Aphids

Aphids are tiny soft-bodied insects that suck the juices from plant leaves. They seldom pose a threat to tree health but can become a nuisance due to the sticky honeydew which drips from infested leaves. Most aphids can only feed on one species of plant or shrub. Thus, aphids infesting street trees will not infest other types of plants on your property. You may also notice ants on aphid-infested trees. Ants feed on the sugary honeydew and do not cause any damage to the tree.

Very few methods of aphid control are currently available. The Board of Parks and Recreation does not spray infested trees with chemical pesticides for the following reasons:

1. We are concerned about public health and safety as well as the environmental impact which may be caused by the application of chemical pesticides
2. Tree health is not jeopardized by these pests
3. Chemical control is extremely costly and is only temporary, as aphids are blown long distances and will re-infest sprayed trees
4. Chemical pesticides can kill or inhibit populations of beneficial predatory insects.

We are concerned about aphid problems and are currently implementing the use of biological controls. These include the use of predatory insects such as ladybeetles. Many predators already do a very good job of controlling aphids on street trees. There is usually a time lag, however, of 1-3 weeks before predator populations catch up with aphid populations. Predators can then become so numerous on leaves that many people mistake them for pests themselves.

For small trees, it may be helpful to blast badly affected leaves and branches with a jet of water in the evening. This physically dislodges and kills the delicate aphids but should not harm predators.