Description of the Pest

Three species of mealybugs in the genus Pseudococcus may infest vineyards: the grape, obscure, and longtailed mealybugs. The primary species of concern in North Coast and San Joaquin Valley vineyards are the grape and obscure mealybugs. In Central Coast vineyards, obscure and longtailed mealybugs can cause damage. In the Coachella Valley, longtailed mealybug may occur. Vine mealybug, Planococcus ficus, is covered in a separate section of this publication.

Life Cycles

Grape and obscure mealybugs lay yellow to orange eggs within an egg sac; longtailed mealybugs give birth to live crawlers. Crawlers of all three species are yellow to orange-brown in color. The grape mealybug has two generations each year and overwinters as an egg or crawler in or near a white, cottony egg sac under loose bark and in the cordons or upper portions of the trunk. In spring most grape mealybug crawlers move toward the base of spurs, or under the loose bark of canes, and then onto expanding green shoots, reaching maturity in mid-May to early June. Most females return to old wood to lay eggs that hatch from mid-June to July. First generation crawlers then move out to the green portions of the vine to feed on fruit and foliage in late June or early July; mostly immatures are seen through July. Adult females will appear in late summer and early fall. Some females will oviposit in the fruit clusters but the majority of the females return to the old wood to lay the overwintering eggs.

Obscure and longtailed mealybugs do not diapause over the winter and have multiple overlapping generations with all life stages present on the vines year round. Obscure mealybug overwinters under the bark of the trunk, cordons, and spurs (the same as grape mealybug). In late spring some obscure mealybugs begin to feed on leaves, but the majority of the population remains hidden under the bark or in the tight clusters.

Appearance

Adults of all three Pseudococcus species are about 0.2 inch long, flat, oval shaped, and have a white waxy covering with wax filaments sticking out from circumference of the body. Longer filaments from the posterior end make these mealybugs appear to have "tails." These filaments are longer than those on the vine mealybug, a newly introduced species that is covered in a separate section.

The grape mealybug and the obscure mealybug closely resemble each other. One method of distinguishing them in the field is to gently probe a female with a sharp point (without puncturing the body) to elicit the release of a defensive excretion. If the color of the fluid excreted is reddish orange, then it is most likely grape mealybug; if it is clear, it is most likely obscure mealybug. Another distinguishing characteristic is based on the different life cycles of the two species: grape mealybug diapauses in winter and has two generations a year that do not overlap. Consequently, if only one or two life stages of a mealybug are present at a given time, it is most likely a grape mealybug because obscure mealybug does not diapause and thus all life stages are present throughout the year.

Longtailed mealybug is similar in appearance to the other two species but has much longer waxy filaments on the posterior end (they are as long or longer than the body of the adult female). Longtailed mealybugs are only a problem in Central Coast vineyards.

Damage

In recent years there have been increases in the number of grape mealybug infestations in the San Joaquin Valley and North Coast and an increase in the incidence of obscure and longtailed mealybugs in Central Coast vineyards. Susceptibility to mealybug damage varies by variety. It is worse on varieties that produce clusters close to the base of the shoot because the fruit often touches old wood. Mealybugs damage grapes by contaminating clusters with cottony egg sacs, larvae, adults, and honeydew. Often the honeydew is covered with a black sooty mold. All three species can transmit grape viruses.

Management

Detecting and marking mealybug infestations during harvest is a key to monitoring populations the following season. Once established, parasites and predators can help keep populations down, but an infestation may slowly spread unless controlled with insecticides. Leaving areas of the vineyard untreated is an effective technique to increase predator and parasitoid populations, however, under heavy population pressure, this may not be feasible. When treating mealybugs, leave at least one out of every 10 acres untreated to provide a refuge for natural enemies, or treat with an insecticide that is not toxic to parasites, see RELATIVE TOXICITIES TABLE.

Honeydew-seeking ants must be controlled in order to allow natural enemies of mealybugs to aid in mealybug control. Controlling ants may sufficiently allow parasites and predators to control mealybugs. Ant control is best accomplished either with tillage, cover crops of common vetch, or ant baits. See the section on ANTS for additional information on control.

Biological Control

Many natural enemies play a part in the biological control of mealybugs. At least five species of parasitic wasps attack grape mealybugs in California. Little research on these parasites has been conducted, but it is assumed they play a prominent role in regulating populations. The impact of the different species varies from time to time and place to place. Grape mealybugs that are parasitized by two tiny wasps, Acerophagus notativentris and Pseudophycus angelicus, have multiple emergence holes that are easily seen with a hand lens. Ants must be controlled to keep them from interfering with these natural enemies. Two parasitic wasps, Pseudophycus flavidulus and Leptomastix epona, have been imported for release against obscure mealybugs but are not commercially available. To ensure survival of parasites, do not use disruptive insecticides during the growing season.

The most effective mealybug predators are lady beetles such as the mealybug destroyer, Cryptolaemus montrouzieri and Hyperaspis sp., which can be found in coastal regions. Cecidomyiid flies prey on mealybug eggs and small larvae. These predators plus lacewings, minute pirate bugs, and spiders are important in keeping mealybug populations in check.

Cultural Control

If gray field ants (Formica spp.) are tending grape mealybug and protecting them from parasites, studies show that planting a cover crop of common vetch (Vicia sativa) can help reduce the number of ants present on the vines. Common vetch has an abundance of extra floral nectaries that attract the ants away from grape mealybug, thus exposing the mealybugs to parasites. In research studies, common vetch was fall seeded in a 80:20 mixture with 20% Merced rye. The cover crop established itself in late fall and winter so that by early spring it was ready to attract the ants. A heavy seeding rate (120 lb/acre) helps to ensure a good stand. The effect of other nectary-bearing cover crops on attracting ants has not been evaluated. (Research using cover crops to attract Argentine ants, Linepithema humile, has not been conducted.)

Training vines so that clusters hang freely and do not touch the wood can also be an effective strategy to reduce grape mealybug infestations.

Monitoring and Treatment Decisions

Monitor mealybugs closely throughout the year. Detection and mapping of populations at harvest is important for monitoring populations the following season. If the vineyard had an infestation at harvest, monitor for mealybugs in late February to early March the following year. (This monitoring can be combined with scouting for other pests as described in DELAYED-DORMANT AND BUDBREAK MONITORING (wine/raisin grapes or table grapes)). Peel back the thin bark on spurs in the current season's prunings or loose bark on canes and look for the presence of grape mealybug crawlers.

To monitor adult activity, grape mealybug pheromone lures are available and are used in red delta traps to monitor for males. There are two grape mealybug male flights per year. Monitoring the spring flight of grape mealybug males can be used to predict the emergence of crawlers of the summer brood and to time control measures. Infestations may be spotted in both summer and winter by looking for the presence of honeydew and sooty mold. Also, look for ants on the vines because their presence is a good indication of a mealybug infestation. If ant activity is high, however, the amount of honeydew on the plant may be minimal because the ants harvest it.

Be sure to monitor parasitism by collecting mealybugs and holding them in gelatin capsules (available from pharmacies) at room temperature for 2 to 4 weeks to detect parasite emergence. If parasitism is found, leaving untreated areas of the vineyard can provide refuges in which the parasites can survive.

If monitoring indicates a small population, a single treatment in the delayed dormant period or spring may adequately control populations. For high infestation levels, treat in the early spring and in the summer. Crawlers and young nymphs are the stages most susceptible to insecticides. Properly timed delay dormant/spring applications target these life stages.

Grape mealybug has two generations a year, with crawlers present from delayed dormancy to early spring and again in summer (June or July). Obscure and longtailed mealybugs do not diapause in winter and, therefore, all life stages can be present in the vines. The most effective treatment timing for these two species is in spring.

Delayed Dormant and Early Spring Treatments

For wine and raisin grapes, if an average of one spur or cane of every five sampled (i.e. 20% or more) has crawlers, a treatment is warranted. If the insect growth regulator buprofezin is used, it should be applied when the majority of the population is in the crawler stage and before shoots are 6" long. For table grapes, the threshold is an average of one spur or cane of every 10 sampled (10% or more). Applications are best made as dilute sprays applied by a ground rig.

Spring Treatments

If an insect growth regulator was not previously used, be sure to monitor in April for immatures under the bark in cordons and spurs. Monitor for mealybugs along with other pests as outlined in MONITORING INSECTS AND SPIDER MITES. If a treatment is needed and a soil-applied neonicotinoid is chosen, select a product that is most effective on the soil type in the vineyard. Specifically, imidacloprid and clothianidin are more effective on light-textured soils, whereas thiamethoxam and dinotefuran are most efficacious on heavy soils.

Summer Monitoring and Treatments

In late May/early June, examine the base of spurs for mature grape mealybug females and/or ant movement on the vine.

• Choose 20 vines from different areas of the vineyard.
• Inspect 1 spur per vine to determine how many of the 20 vines are infested. Note that ant movement and honeydew are signs of mealybug presence.
• Record each vine that has a spur with grape mealybug on a monitoring form (example form—PDF).
• Treatment may be warranted if 20% or more of the spurs on wine and raisin vines are infested with female grape mealybug; the threshold for table grapes is 4%.
• Be sure to monitor parasitism by collecting mealybugs and holding them in gelatin capsules at room temperature for 2 to 4 weeks to detect parasite emergence. If parasitism is found, untreated areas of the vineyard can provide refuges for parasites.

Cluster Monitoring

Clusters that touch old wood can also be monitored during the period from June 15 to July 15. If no crawlers are detected in the clusters, little or no infestation is present. If a single treatment is applied in summer, make a foliar application in June, 1 to 2 weeks after egg hatch. Be sure to make summer treatments when mealybugs are small and vulnerable; once they are more than half-grown, foliar treatments may not be effective.

For raisin and wine grapes, dilute applications can be made, however after veraison on table grapes make concentrate foliar applications to avoid berry spotting. It is important to note that once mealybugs have moved into the clusters and after bunches in wine grape varieties have closed, foliar treatments are not effective. Educate field workers or harvest crew to recognize mealybug cluster infestations and flag the vines for treatment.

Postharvest Treatments

Postharvest treatments are not effective against Pseudococcus mealybugs because the majority of the population is in the egg stage under the bark and not vulnerable to foliar treatments at this time.

Pesticides and Natural Enemy Releases

Important Links

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