Grape mealybug, Pseudococcus maritimus (Ehrhorn)

The grape mealybug is white with a flattened, oval shape. Filaments protrude along the perimeter of the body, the longest protruding from the rear. First instar nymphs overwinter in a white cottony ovisac produced by the female in the fall. They become active in April or May, disperse over the vine, and begin to feed at bases of shoots or pedicels of grape clusters. Numbers are usually not high enough for damage to be caused at this point. Adults appear in late June and ovisacs containing eggs are deposited beneath loose bark. Young nymphs appear a few days later and may get into fruit clusters or feed on leaves near veins. Adults again appear in late August.  All stages may be seen on vines in autumn.   Egg-laying continues until cold weather, but eggs that do not hatch before winter do not survive.

Populations are most likely to develop on vigorous vines with heavy foliage that supplies greater shade and nutrition. Vine growth is vigorous enough that the vine can tolerate this type of injury in most cases. The problem from mealybug arises from the honeydew, the excretory product of the insect - mostly excess sap, containing high sugar levels. This honeydew accumulates on fruit and foliage, supporting the growth of dark sooty mold fungus. Sooty mold presents a cosmetic problem, mainly of concern in table grapes. In wine grapes this is not an issue. However, high populations feeding on and near clusters can cause clusters to drop before harvest.  Another important concern is the role in mealybugs serving as the vector for grapevine leafroll virus.  Avoid the use of insecticides that are disruptive to poputions of natural enemies; parasitoids often provide important natural control of mealybugs.  Where grape mealybug is expected to be a problem, it is more severe on late-ripening varieties. Early-maturing varieties are harvested before the second (summer) generation has had much of an impact. Injury is usually not severe, and natural enemies generally provide control.

Grape mealybug is by far the most common in eastern states.  In California, two additional species may present problems, the obscure mealybug, Pseudococcus viburni, and the vine mealybug, Planococcus ficus.  When poked, grape mealybug exudes a red fluid (ostiolar fluid), compared with clear fluid in the other two species.  Vine mealybug is more bluntly oval and with short terminal filaments, compared with the more elongate oval and long terminal filaments of the other two species.  Recent work in California has shown that grape mealybug, as well as the others, are capable of transmitting grapevine leafroll virus.

If infestations are severe at harvest, apply a delayed dormant spray the following spring.  This may provide adequate control; a summer spray may be needed.

See comments from California, where an action threshold for wine grapes of 20% infested spurs has been suggested. Applaud (buprofezin), Venom (dinotefuran) or Assail (acetamiprid) or Admire Pro (imidacloprid) may be used.  If chemical control is used, leaving a section of the vineyard unsprayed will allow a refuge for natural enemies.  See also the Practical Winery article comparing the appearance and biology of the three species.

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