Pear psylla adults, Cacopsylla pyricola, look like small cicadas. They are about 1/10 inch long and are dark reddish brown. The adults, which overwinter on trees or other sheltered places, become active any time the temperature is above 40°F. Females begin laying tiny, pear-shaped, yellowish eggs in cracks in the bark and around the buds in late March and continue through the white bud stage. The peak of egg laying is green tip to green cluster bud. Eggs hatch in 2 to 4 weeks, and the yellowish, wingless nymphs move to succulent stems and developing leaves to feed. Nymphs are flattened, covered with honeydew, have sucking mouth parts, and feed on plant sap. Four to five generations are born each year.
The pear psylla secretes large amounts of honeydew, which runs down over foliage and fruit and in which a sooty fungus grows. This causes the skin of the fruit to become blackened and scarred and the foliage to develop brown spots. Heavy infestations can cause partial to complete defoliation of trees, reducing vitality and preventing the formation of fruit buds.
Orchards with a history of severe psylla infestations should receive an intensive insecticide program beginning in the dormant period. To prevent egg laying, oil should be applied in mid-March to early April, depending on the location in the state. At green cluster bud, a treatment of oil plus a pyrethroid compound should be applied. If psylla are still present at petal fall, begin kaolin clay (Surround) applications at about 10-day to 2-week intervals. Shorten spray intervals if psylla persist. Good spray coverage is essential to controlling this difficult pest.