Leafhopper nymphs are whitish green, smaller, and wingless, and are usually found on the undersides of older leaves. Photo by G. Krawczyk.
As opposed to rose and potato leafhoppers, this species' primary host is apple. Its pest status relates to its injury to the leaves, excrement on the fruit, and nuisance to workers. The importance of this pest has been greatly reduced since the introduction of the neonicotinoid insecticides, which are extremely effective on it when used at petal fall for plum curculio control.
Description and life cycle
Adults are white and 1/8 inch long. Leafhopper nymphs are whitish green, smaller, and wingless, and are usually found on the undersides of older leaves. They move quickly sideways as well as forward.
White apple leafhoppers overwinter as eggs in the bark of 1- to 5-year-old wood. Hatch begins at pink and may continue for 3 to 4 weeks during May and June when weather is variable. The nymphs develop over several weeks. Adults then lay eggs in the petiole and veins of leaves. Second-generation eggs begin to hatch during late July and August. The nymphs feed during August and are fully grown by late August or September. Overwintering eggs are laid during September and early October.
White apple leafhopper adults and nymphs feed on leaves and do not directly attack the fruit, although excrement on the fruit can reduce its quality. Leaves become speckled or mottled with white spots as green tissue is destroyed where leafhoppers suck sap from the leaves. Abundant adults during harvest can be a severe nuisance factor.
One leafhopper per leaf during first-brood activity (petal fall to second cover) is justification for applying an insecticide. Populations of two or more leafhoppers per leaf during second-brood activity in August and September should be treated. Examine five trees per block, 20 leaves per tree, and check the undersides of leaves for nymphs.
Young leafhoppers are much easier to control than adults. Effective control of the first generation may directly reduce high populations of the second. The first generation is a better target since the hatch is fairly synchronous, and leafhoppers of the age vulnerable to insecticides are present at one time. Also, insecticides may be used at lower rates since less foliage is present during the first generation. Thorough coverage of upper and lower leaf surfaces is necessary and considered essential for effective control. Specific chemical recommendations for home gardeners are in Fruit Production for the Home Gardener, and recommendations for commercial growers are in the Penn State Tree Fruit Production Guide.