Physical and cultural controls
On shrubs and garden plants, aphids can sometimes be controlled by simply washing them off the plants with a strong stream of water. Hosing plants can lethally injure aphids and very few surviving aphids that are knocked to the ground may successfully find their way back to their host plant.
Some flowers that are perennial, but die back to the ground in the fall, have problems with aphids in the spring. Columbine, lupines, and perennial asters are examples. With these plants, aphid eggs are laid on the leaves and stems in the fall. The eggs hatch in the spring, and if new growth has emerged by that time, some of the newly hatched aphids may find their way onto the growing plant. This database d can be prevented by removing the old top growth containing the eggs before the plants bolt in the spring. This plant material can be safely composted or piled elsewhere, as the aphids that hatch from the eggs will only be able to move very short distances (inches) before they die.
Chemical controls
When large numbers of aphids occur regularly and damage plants or shoots are not sufficiently controlled by biological controls, insecticides can be used to control aphids. These are used in several ways.
Dormant Season Oil Applications. Horticultural oils (Fact Sheet 5.569, Insect Control: Horticultural Oils) have a special place in aphid control, to kill the egg stages during the dormant season. Horticultural oils act largely by smothering insects; their use for aphid control would require that they cover the eggs, which are the overwintering stage in some types of aphids on trees and shrubs. They would be applied as sprays sometime before bud break, during the dormant season.