How to Manage Pests
UC Pest Management Guidelines
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 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 poke 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.
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.
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 untreated areas in the vineyard is effective in increasing predator and parasite 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 with sprays of chlorpyrifos (Lorsban) directed at the soil surface. Chlorpyrifos may only be used for either mealybug control in grapes in a given year or for ant control but not both. See the section on ANTS for additional information on control.
The most effective mealybug predator is a lady beetle called the mealybug destroyer, Cryptolaemus montrouzieri, 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.
Grape mealybug infestations can also be reduced by training vines so that clusters hang freely and do not touch the wood.
and Treatment Decisions
Be sure to monitor parasitism by collecting mealybugs and holding them in gelatin capsules (available from pharmacies) 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 that population levels are low, a single treatment in the delayed dormant period should be adequate. For high infestation levels, treat both in the delayed dormant season (January to March) and in summer. Crawlers and young nymphs are the stages most susceptible to insecticides.
Grape mealybugs have two generations a year, and crawlers are present from delayed dormancy to early spring and again in summer (June or July). The most effective treatment timing is when crawlers are present. Obscure and longtailed mealybugs do not diapause in winter and, therefore, all life stages can be present in the vines. Studies indicate that the most effective treatment timing for these two species is in the delayed dormant period (chlorpyrifos) or in late spring (imidacloprid).
Delayed dormant treatments. If the vineyard had an infestation at harvest, monitor for mealybugs in late February to early March. (This monitoring can be done along with monitoring 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 and look for the presence of crawlers. 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 delayed dormant treatment is warranted. For table grapes, the threshold is an average of one spur or cane of every 10 sampled (10% or more). Record results on a monitoring form (example form— . Applications are best made as dilute sprays applied by a ground rig.
Spring treatments. If a delayed dormant treatment was not applied, be sure to monitor in late March or 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.
Summer treatments. In late May/early June, examine the base of spurs for mature grape mealybug females and/or ant movement on the vine.
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.
On raisin and wine grapes, make a dilute application, whereas only make concentrate applications on table grapes at this time of year 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 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.
UC IPM Pest Management Guidelines: Grape
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