During the 2000 grape harvest, consultants and inspectors in southern Michigan reported some sooty black grapes and the associated pest insect. This has been identified as the grape mealybug (Pseudococcus maritimus). In an effort to help growers and crop scouts identify this insect, a description and photographs are provided here.

 Grape mealybug overwinters under loose bark or in crevices. As temperatures increase in the spring, the yellow-brown ‘crawler’ stage moves to the clusters and developing foliage to feed. The insect grows through a sedentary nymph stage and then becomes an adult. Adult males are small with wings, while adult females (see photograph above) are up to 3/16 inches long, with waxy filaments around the body. This mid-summer generation reproduces, creating a second generation that reaches maturity late in the season.

Vines can tolerate the removal of sap by mealybugs, but their excrement is the main cause of damage. The blackening of grapes shown in the photograph below is caused by sooty mold fungus that develops on the honeydew secretion. Berries harvested with this damage (especially white varieties where it is more apparent) are likely to be rejected for failing cosmetic standards.

Mealybugs are naturally kept under control by lacewings, ladybirds, pirate bugs, and spiders. These can attack mealybugs in hard-to-reach places. Maintaining a pest management program that does not destroy your bio-control agents is the easiest way to avoid mealybug problems.

Chemical control works best when sprays are aimed at the mobile crawler stage. When mealybugs are in the egg sac, or settle and are covered with wax, it is harder for insecticides to reach them. Addition of oil to a dormant spray has been recommended in California to increase penetration of insecticides into cracks. Both Provado (1 oz/acre) and Guthion (2 lb/acre) are registered for mealybug control in grape. Timing will be critical to effectiveness of any management plan.

We currently do not have much experience with mealybugs or with their management in Michigan vineyards. If you detect mealybug in your vineyard, please contact your extension agent or call us at the MSU Small Fruit Entomology Lab so we can arrange a visit: (517) 432-9554. We hope to learn more about this pest during 2001.

For more information on this pest, these websites focus on grape mealybug:

http://www.msue.msu.edu/vanburen/fgmbug.htm
http://www.ipm.ucdavis.edu/PMG/r302301811.html