These insect pests, similar to aphids, can damage the tender growth of trees by sucking out the plant's juices. They also secrete honeydew that coats leaves and may encourage the growth of a sooty black mold. Symptoms of damage include yellowing and dropping leaves.
To control these pests, spray with insecticidal soap every 3-4 days until the insects are gone. In fall, spray trees with a light horticultural oil and, in early spring, spray trees with a dormant oil before the leaves emerge. After the leaves emerge, spray insecticidal soap once a week for 3 weeks.