Fruit Crops

New White Apple Leafhopper Information May Benefit Biological Control

White apple leafhopper (WALH) is a common sap-sucking insect that feeds on apple from coast to coast. In some areas, insecticide resistance has been confirmed, and WALH numbers and damage have increased. Growers cite four reasons for chemical control: (1) the noticeable stippling on foliage caused by feeding, (2) assumed damage to fruit yield or quality, (3) the dark varnish-like excrement spots on the fruit, and (4) the nuisance to pickers of high second generation populations. Therefore, growers with noticeable populations may use as many as 2-3 insecticide applications per season for control. Because of resistance to organophosphate insecticides, growers have relied primarily on synthetic pyrethroids and carbamates for WALH control that are often toxic to predaceous mites important in mite IPM programs, as well as other beneficials.

Recent research has demonstrated that relatively large populations of WALH have no effect on fruit weight, firmness, color, soluble solids, return bloom, or return crop. A study in Virginia on first generation leafhopper recommended changing the action threshold for first generation from the current 0.25-0.5 leafhoppers per leaf, to a more realistic 3-4 leafhoppers per leaf. A second study, in Washington, showed that populations up to 6.5 WALH nymphs per leaf caused no injury, and that such levels did not warrant spraying. The reduction in use of broad spectrum pyrethroid and carbamate insecticides will likely benefit the conservation of predatory mites and other important natural enemies in apple. Furthermore, WALH itself has natural enemies, notably Anagrus epos, a tiny mymarid wasp that parasitizes WALH eggs. The reduction in use of broad spectrum insecticides could also conceivably conserve Anagrus and improve biological control of WALH.


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