Vine Mealybug

Vine mealybugs are small (adult females are about 1/8 inch in length), soft, oval, flat, distinctly segmented, and covered with a white, mealy wax that extends into spines (filaments along the body margin and the posterior end). The vine mealybug has a pinkish body that is visible through the powdery wax, and it is slightly smaller than the Pseudococcus mealybugs. The waxy filaments that protrude from the body of the vine mealybug are shorter than those on the Pseudococcus mealybugs, and the vine mealybug does not possess long tail filaments. The adult male is smaller than the female, has wings, and flies short distances to mate. There are three to seven generations a year.

All or most life stages of the vine mealybug can be present year-round on a vine depending on the grape-growing region. In the North Coast during winter months, the only life stages found are nymphs located under the bark predominately at the graft union, on trunk pruning wounds, and below the base of spurs. In other regions during the winter months, vine mealybug eggs, crawlers, nymphs, and adults are under the bark, within developing buds, and on roots.

As temperatures warm in spring, vine mealybug populations increase and become more visible as they move from the roots or trunk to the cordons and canopy. By late spring and summer, vine mealybugs are found on all parts of the vine: hidden under bark and exposed on trunks, cordons, first- and second-year canes, leaves, clusters, and roots. Ants may transport vine mealybug from the roots to above ground plant parts where they continue to tend vine mealybugs throughout the remainder of the growing season.

In the North Coast, vine mealybug has not been found on vine roots; however, in other regions with sandy soils it spends the winter almost exclusively on the root system. Other mealybugs found infesting grapes are only found on the aboveground portions of the vine. In addition, the vine mealybug is much more likely to be found on leaves during the growing season than the other mealybugs. During summer when vine mealybugs are in the canopy, they can be located well above the fruit zone and will lay eggs on the leaves, while Pseudococcus mealybugs do not. Vine mealybug does not diapause during the winter, and it appears to be more sensitive to cold temperatures than grape mealybug.

Damage by the vine mealybug is similar to that of other grape-infesting mealybugs in that it produces honeydew that drops onto the bunches and other vine parts and serves as a substrate for black sooty mold. If ants are not present, a vine with a large population of this pest can have so much honeydew that it resembles candle wax. Also, the mealybug itself will be found infesting bunches making them unfit for consumption. Like the grape, obscure, and longtailed mealybugs, vine mealybug can transmit grapevine leafroll-associated viruses.

Vine mealybug occurs in all major California production areas. In California, the vine mealybug feeds predominantly on grapevines, although in other countries it can be a pest of fig, date palm, apple, avocado, citrus, and a few ornamentals.

Because several different species of mealybugs may infest grapevines, it is important to know which species of mealybug is present because management programs for the various mealybugs differ. If you find mealybugs in your vineyard, collect the largest mealybugs you can find and place them in a jar of alcohol or sealed plastic bag. Take the sample to either your University of California Cooperative Extension (UCCE) farm advisor or county Agricultural Commissioner.

The parasites that attack Pseudococcus mealybugs do not attack the vine mealybug; therefore two potential candidates for biological control have been imported and released in California. The most successful of these has been Anagyrus pseudococci. This species has provided up to 20% parasitism in some vineyards in the Coachella Valley and up to 90% parasitism of exposed mealybugs late in the season in the San Joaquin Valley. This parasitoid can be highly effective late in the season to reduce mealybug populations present after harvest before they return to the roots or lower trunk to overwinter. However, in the spring, the parasitoid does not emerge from its overwintering state until about bloom, providing minimal mealybug suppression during the early and midseason. Growers can attempt to overcome this biological limitation of A. pseudococci by doing early-season releases of parasitoids that are purchased from commercial insectaries. Management of ants can reduce disruption of parasitism by A. pseudococci.

In coastal regions, several lady beetles such as the mealybug destroyer, Cryptolaemus montrouzieri and Hyperaspis sp. attack vine mealybug eggs and crawlers. Larvae of predaceous midges (family Cecidomyiidae) feed on mealybug eggs.

The female and nymphal mealybugs are wingless and are unable to fly so they must be carried by humans, equipment, wind, birds, or be present on vines at the time of planting. Do not allow contaminated equipment, vines, grapes, or winery waste near uninfested vineyards. Movement of equipment that pushes brush or any over-the-row equipment can be a major source of infestations in new locations; steam sanitize equipment before moving to uninfested portions of the vineyard. Do not spread infested cluster stems or pomace in the vineyard. To reduce contamination, cover all pomace piles with clear plastic for several weeks, and avoid creating piles that consist predominately of stems.

Reduce cluster infestation by pruning vines to prevent clusters hanging directly on the cordon. In areas where mealybugs overwinter exclusively on the roots, band application of Tanglefoot onto duct tape that has been wrapped around the trunk (with the bark removed) may help slow crawler movement up the vine in the spring.

Biological and cultural controls are organically acceptable management tools. Repeated applications of oil approved for organic production can suppress vine mealybug in wine and raisin grapes. Oil applications are not used in table grapes, because they potentially affect the appearance of the fruit surface. Additionally, there are concerns about using oil in conjunction with sulfur due to the potential phytotoxic effects. Mating disruption is also approved for organic vineyards.

Monitoring

Monitor for vine mealybug by doing searches on the roots, trunk, cordon, leaves, and clusters depending on the time of year.

During the winter, look for vine mealybug on the lower crown; in areas with sandy soils, on the roots. During budbreak follow the monitoring guidelines in DELAYED-DORMANT AND BUDBREAK MONITORING (wine/raisin grapes or table grapes) to monitor these and other pests and record results on a monitoring form (example form—PDF).

In the spring, monitor the crown and trunk for adult females and the presence of crawlers moving up the vine. Starting at bloom, monitor for vine mealybug along with other pests as outlined in MONITORING INSECTS AND SPIDER MITES. Survey cordons, canes, and basal leaves. In coastal areas, also continue to monitor the trunk.

When fruit is present, especially after veraison, monitor clusters to ensure vine mealybug life stages or honeydew are not contaminating the fruit. In table grapes and other hand-harvested vineyards, picking crews can be trained to be a valuable resource for reporting the presence of mealybugs in vineyards not known to be infested.

Monitoring efforts can be aided by looking for ants and honeydew. Argentine and gray ants tend vine mealybugs; therefore, observing ant activity can direct ones attention to where mealybugs are present on the vine. The presence of honeydew may also be an indication of vine mealybug presence. Thus, when searching for vine mealybugs during summer, look for honeydew exudates on the clusters, trunk, and cordons. These exudates will resemble melted candle wax; if the infestation is severe, basal leaves will appear shiny and sticky. Eventually, sooty mold will grow on the honeydew and permanent parts of the vine will appear greenish black during the fall and winter.

Pheromone traps can help determine if vine mealybug is present within or near your vineyard. Place pheromone lures in small red delta traps in and around the vineyard by April 1 in the southern San Joaquin Valley, by May in areas further north, and by June in the North and Central Coast region:

• Choose two trap sites for each 20-40 planted acres.
• Put one trap in the center of the block and the other on the edge near a staging area. These traps can attract vine mealybug males from as far away as 1/4 mile.
• Attach traps to the trellis wires so that they are in the cluster area.
• Label the trap with the block name and row number of its location and the dates it remains in the vineyard.
• Check traps for the presence of male vine mealybug every 2 weeks through November.
• Follow the manufacturer's recommendations for storing and replacing pheromone lures.
• Record observations on a monitoring form (example form (PDF)

It is essential to use a dissecting microscope to identify the male mealybug. (Male vine mealybugs are smaller than adult thrips and are very difficult to see even with a hand lens.) The sex pheromone is specific to the vine mealybug, but the traps may also contain other male mealybugs depending on the site. If there are questions as to the identification of the mealybug species, take samples to a farm advisor or county agricultural commissioner or refer to the Male Vine Mealybug Identification Sheet.

The number of males found in a trap depends upon its proximity to the infestation and to the time of year. In the North Coast, new infestations have been located near traps that caught very low numbers in June (5 to 10 males per trap per week) and high numbers in fall (more than 50 males per trap per week). In the San Joaquin Valley, an infested vineyard will have between 20 to 300 or more males per trap per week. In either region, low numbers of male vine mealybugs found in a trap may mean that the infestation is located in an adjacent block or in a more distant vineyard. If males are found, increase the number of traps in the vineyard, and locate the infestation by examining lower leaves for honeydew.

Treatment

If vine mealybug is found in a vineyard, treatment is recommended. However, the level of treatment varies greatly depending on the region, type of grape, and harvest date:

• Coastal regions only have two to three generations of vine mealybug per year, compared to five to seven in the lower San Joaquin Valley.
• Table grapes have no allowance for mealybugs in the cluster, while wine grapes can tolerate low levels.
• Harvest dates vary widely in table grapes. Fruit from a Flame Seedless vineyard, harvested on the first of July, is less susceptible to damage than fruit in a neighboring Crimson Seedless vineyard, which might be harvested in October.

Due to the complexity of these and other factors, such as biological control, decisions about the level of mealybug control need to be made on a vineyard-by-vineyard basis.

In vineyards with low mealybug pressure, a single insecticide application in the spring or at bloom is often sufficient for season-long mealybug control. Effective control in heavily infested table grape vineyards, planted to a late-harvested variety, may require three or more treatments.

When treating for vine mealybug, consider other pests. Insect growth regulators can control scale pests, spirotetramat provides suppression of nematodes and phylloxera, and neonicotinoids are effective against sharpshooters and leafhoppers. When using soil-applied neonicotinoids, growers should also be cognizant of soil type: imidacloprid (Admire Pro) and clothianidin (Belay) are more effective on sandy soils whereas thiamethoxam (Platinum) and dinotefuran (Venom) are more effective on heavier soil.

Mating disruption has recently become available and can be used as an alternative or supplement to chemical control. Mating disruption is most effective when insecticides are used aggressively in the first year to reduce vine mealybug to low densities. In subsequent years, mating disruption supplemented with insecticides (as needed) can maintain the population at low levels. Mating disruption is most effective when applied over a large area (10 acres or greater). Greater success has been achieved in northern California, where there are fewer generations of vine mealybug per year.

• Delayed/dormant budbreak monitoring form (PDF)
• Insect and spider mite monitoring form (PDF)
• Photos of mealybugs