Caged ‘Concord’ grapevines were artificially infested with “low” and “high” populations of the leafhopper,Erythroneura comesSay, between early July and late August from 1979 to 1982. Foliage injury became evident shortly after the first introductions and increased during the season. At harvest, the injury inflicted by the “high” populations in the caged vines was similar to or higher than the injury inflicted by natural populations ofE. comesin commercial vineyards. The caged grapevines injured byE. comesproduced fruit yields and juice quality that did not differ significantly from the noninfested caged vines. In addition, vine vigor was not reduced by the leafhopper injury. Concord vines may be able to withstand greater injury from first- and second-generationE. comesthan was previously believed. Lacking in this study was foliage injury that may occur during June from overwintered leafhoppers as they first enter vineyards. This is the main period of berry and cluster primordia initiation, the major contributing factors to fruit production.