Scientists are testing different populations of vine mealybug from California’s Coachella and San Joaquin Valleys susceptibility to the five most common pesticides used in the past few years to control them.

With funding from the University of California (UC) exotic/invasive pests and diseases research program, UC Riverside Cooperative Extension Viticulturalist Carmin Gispert and Entomologist Nilima Prabhaker tested the mealybug’s reactions to chlorpyrifos, dimethoate, methomyl, buprofezin, and imidacloprid, and found different responses between populations to some insecticides.

In laboratory experiments, vine mealybug populations from the Coachella and San Joaquin valleys are most sensitive to chlorpyrifos, based on the lethal concentration that kills 50 percent of the population, followed by buprofezin.

Buprofezin was the most effective against the immature stages of vine mealybug due to the material’s ability to inhibit molting. It is especially active against the first and second immature stages of the pest.

Application timing is particularly important when using buprofezin since it’s effective on the immature stages of the pest and doesn’t kill adults.

By contrast, imidacloprid was more active against the older immature-stage insects and adult vine mealybugs, but not the crawlers.

The continuation of this study has implications for refining management programs for the mealybug, including vine monitoring to determine the most accurate timing of applications of the insecticides to target the pest’s most susceptible development stages according to the insecticide being used.

The researchers are obtaining baseline information. Future tests will help determine if the reduced efficacy of some insecticides is related to resistance of the pest to some of the insecticides. These data will help pest control users choose which treatments are best in particular situations. To date, the California Department of Food and Agriculture has reported that 17 California counties are infested with vine mealybug.

Once established, the pest is difficult to eradicate. In California, it occurs in the Coachella and Central valleys, the Central and North coasts, and the Sierra foothills. The host range of the mealybug includes grape, fig, date palm, apple, avocado, citrus, and a few ornamentals. Currently, the pest has been found feeding only on grapevines in California.

Vine mealybug produces a sticky, sugar-laden substance called "honeydew" that promotes mold and bacterial growth and damages fruit clusters to the point where they can't be marketed.

Cultural control

Gispert said biological and cultural controls are organically acceptable management tools. The female mealybug is unable to fly, so humans, equipment, wind, or birds can carry the pest.

Gispert said, “Don’t allow contaminated equipment, vines, grapes, or winery waste near uninfested vineyards. Growers should steam sanitize equipment before moving it to uninfested portions of the vineyard.

“Don’t spread infested cluster stems or pomace in the vineyard, compost, and/or cover all pomace piles with clear plastic for at least two weeks.”

Biological control

Two potential parasites for natural control have been imported and released in Riverside, Kern, and Fresno counties.

The most successful has been Anagyrus pseudococci. This species has been shown to parasitize up to 20 percent of the mealybug in some vineyards in the Coachella Valley and up to 90 percent in the San Joaquin Valley.

It is extremely important to conserve parasites because they are active late in the growing season and can reduce vine mealybug populations before the pest begins to move to the lower part of the trunk in October.

For more information about vine mealybug, visit the UC Statewide Integrated Pest Management Program Web site at www.ipm.ucdavis.edu.