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April 19, 2007

Vine mealybug life stage influences response to insecticides

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

   Grape clusters contaminated with vine mealybug.
  

Grape clusters contaminated with vine mealybug.
Photo by Carmen Gispert

With funding from the UC Exotic/Invasive Pests and Diseases Research Program, Carmen Gispert, University of California (UC) Cooperative Extension, Riverside, and Nilima Prabhaker, Entomology, UC Riverside, tested the mealybugs’ reactions to chlorpyrifos, dimethoate, methomyl, buprofezin, and imidacloprid and found different responses between populations of the pest to some of these insecticides.

In laboratory experiments, vine mealybug populations from 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 its ability to inhibit molting, and it is especially active against the first and second immature stages of the pest. Application timing is particularly important when using buprofezin since it is effective on the immature stages of the pest and does not 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 emphasizing monitoring the vines to determine the most accurate timing of applications of the insecticides to target vine mealybug’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 these insecticides. This data will help pest control users to choose which treatments are best in particular situations.

To date, the California Department of Food and Agriculture reports that 17 California counties are infested with vine mealybug.

Once established, the bug is difficult to eradicate. In California, the vine mealybug 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 says 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 says, “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 of these 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 parasitism 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.

Resources

High-resolution image (464KB) "Grape clusters contaminated with vine mealybug." Photo credit: Courtesy of UC Statewide IPM Program, by Carmen Gispert. Photos are for use with this release only. All other uses see Legal Notices.

Vine Mealybug on Grapes.

Contacts

Stephanie Klunk, Communications Specialist
UC Statewide IPM Program
(530) 754-6724

Carmen Gispert
UC Riverside
(760) 863-8294

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