Leafhoppers

There are two generations of white apple leafhopper per year. Eggs of this species overwinter in the apple trees and hatch shortly after bloom. Adults of the first generation appear in the last part of May to early June. Nymphs of the second generation develop in July and August.

Rose leafhoppers do not overwinter in apple trees; instead they overwinter on plants of the rose family such as blackberries. In spring, the first generation develops on the overwintering host; adults then migrate to other hosts, including apples. The second generation and apparently a third generation may be spent on apples. This species often reaches great abundance near to or after apple harvest.

The adults of both species are white, about 0.12 inch long and cannot be readily distinguished from one another. Rose leafhopper populations can be identified by the presence of black spots at the base of thoracic setae on older nymphs; these spots are not found on nymphs of the white apple leafhoppers.

Leafhoppers feed by sucking on leaf tissue. Their feeding causes a white stippling on leaves. In heavy infestations, fruit may be reduced in size and buds may be weakened. Excrement dropped by leafhoppers will appear as black specks on apples. These specks are easily removed by washing. Leafhoppers also produce honeydew, which forms into sticky droplets around the calyx end after rainfall or overhead sprinkling, and is not easily removed.

White apple leafhopper has become an increasing problem in the past decade because it has developed resistance to organophosphate insecticides. Start monitoring at petal fall to determine need for treatment.

Parasites of the white apple or rose leafhopper have not been studied in California apple orchards. In other areas, parasitization of eggs may be significant in holding populations in check.

Insecticides are most effective when applied during the first four nymphal instars of the first generation, especially in the fourth instar. These stages occur between petal fall and the first codling moth spray. Start monitoring for this leafhopper at petal fall. At weekly intervals sample four leaves per tree from 25 trees dispersed throughout the orchard. Peak nymphal emergence typically occurs 3 to 4 weeks after the first nymphs are found. Treatment is warranted when populations exceed an average of 0.5 nymphs per leaf or when 30% of the leaves are infested. Rose leafhopper is a concern when high populations of nymphs exist near harvest; treatment of nymphs may be warranted at this time.