Grape mealybug—Pseudococcus maritimus
Grape mealybugs are soft, oval, flattened insects. Their bodies are distinctly segmented; divisions among the head, thorax, and abdomen are not distinct.
The adult female is about 5 mm long and appears smoothly dusted with a white, mealy, wax secretion. Long caudal filaments along the lateral margin of the body become progressively shorter toward the head. A newer vine mealybug has recently invaded California vineyards. This species has shorter filaments than the grape mealybug.
In summer, first-generation crawlers move out from bark to infest fruit and foliage mid-June to mid-July. Some females mature in late August to September and lay eggs on fruit; most return to old wood to lay overwintering eggs. In early spring, crawlers move from bark to new shoots.
Mealybugs excrete large quantities of sticky honeydew, which drips onto fruit clusters and later turns black from sooty mold. Some berries may crack. Mealybugs do not injure vines.
Remove loose bark in winter; young mealybugs and eggs are concealed in such places until spring. High temperatures in June kill much of the most damaging brood. Control of ants (which interfere with natural enemies) is important. Oils applied during grapevine dormancy can reduce numbers somewhat.
For more information about other mealybugs and their management, see the Pest Notes: Mealybugs.