BY Laura Breyer

Growers in Napa and Sonoma Counties are approaching the fifth year of living with vine mealybugs (Planococcus ficus [VMB]) and are developing management programs based on University of California (UC) recommendations, modified by their own inventiveness.

Initial infestations are usually found in the late summer, and are treated very aggressively with foliar applications of Lannate (methomyl) or other broad spectrum insecticides to reduce the mealybug population and to keep them from spreading. (Lannate has a 21-day REI when applied after August 15 due to California Worker Protection Standards, not seven days as on the label.)

Bark stripping, though laborious, can also be part of this aggressive strategy. It allows better contact of the spray material on VMB residing under the bark on trunks and cordons.

Some growers have even tried removing infested vines. In the first years after VMB appeared in California, these intensive efforts were aimed at eradication. However, even though populations may be reduced to below detectable levels for a year or two, they eventually come back to unacceptable levels. It can be very difficult to ascertain if a vine has mealybugs or not, due to the very small size of the crawler stages.


VMB was not the only mealybug causing trouble in 2005. Grape mealybug (Pseudococcus maritimus [GMB]), and the less common obscure mealybug (P. viburni [OMB]) populations were unusually high, obligating many growers to treat mid- to late-season for control of mealybugs already fairly well hidden in clusters. The successes here may translate to VMB management.

After mealybugs move into the clusters, foliar-applied materials often have very little benefit for mealybug control, most likely due to the difficulty of getting coverage in the clusters when mealybugs are still small enough to control easily.

Dana Grande, viticulturist with Jordan Vineyard & Winery (Healdsburg, CA), used 8 oz of JMS Stylet-oil and 12 oz per acre of Applaud (buprofezin) in 100 gallons [water] per acre, directed at grape mealybug crawlers in grape clusters in early August. Three weeks after treating, Grande reported, “Unbelievable control … I couldn’t find one mealybug in the clusters.”

Don Mitchell with Purity Products (Healdsburg, CA) achieved excellent control of grape mealybug in Carneros Chardonnay clusters in late summer with dimethoate at 2 qt in 400 gallons [water] with an organosilicon spreader. Dimethoate is generally on the wane as a highly-regarded pest management tool due to its association with disrupting mite populations and potential human health risks being an organophosphate, but as an inexpensive rescue tool in mealybug management, it can play a role if utilized correctly.

For vineyards with heavy clay soils where Admire (imidacloprid) is ineffective against mealybugs, Valent has a new “Venom” neonicotinoid product (dinotefuron) that acts systemically like Admire but may perform better in heavy soils. (The cautious grower may want to test this new material on a small acreage in a mealybug-infested site before large application.)

The application method differs significantly from Admire; company representatives recommend putting Venom in towards the end of a chemigation cycle, since it moves readily and will travel past the root zone if put in at the beginning of an application, as is done with Admire. Contact your PCA or Valent representative for more specific information.

One important difference in the overall chemical management of VMB compared to GMB or OMB is that a post-harvest foliar insecticide application is recommended to reduce VMB populations from spreading on wind-blown leaves and returning to the trunk and cordons to over-winter.

Treating for GMB or OMB after harvest is not recommended since GMB or OMB have generally moved out of the canopy by that time. See PWV (Jan/Feb 2006) for a detailed article on the biology and identification of each mealybug species (“Which Mealybug is it, and Why Should You Care,” L.Varela, et al).

Not only were mealybug populations elevated in 2005 in the Napa and Sonoma region, but the population of ants tending mealybugs in vines was also noticeably higher. In many older vineyards that I monitor, GMB (and less commonly OMB) is an innocuous part of the bioscape and rarely an economic pest. When monitoring mealybug nymph populations in the future, I will be more likely to trust noticeable increases in ant activity as an additional indicator of unusually elevated mealybug populations.

If there are many active ants in the vines again, I will target ants on the ground with a strip-spray Lorsban (chlorpyrifos) treatment. This is because GMB and OMB are generally under fairly good biological control in the grape canopy when the predators and parasites are undisturbed by ants or pesticides.

It is important to note that Lorsban can only be used for ant control or as a dormant vine spray for mealybug control, but not for both pests in one season. Although VMB is currently not as well-managed with bio-control in California, reducing the ant population will likely help increase predation of the mealybug population; one component in an overall management strategy.

Ant bait stations are being developed and they will be welcome additions for all mealybug integrated pest management (IPM) programs. Kent Daane and other UC researchers are working on the main culprit Argentine ant (Linepithema humile), studying its biology and behavior in the field so we will know when, where, and how to best deploy the stations. Bayer and other companies are working on registering effective materials. Regulatory agencies are working on approving bait stations and chemical materials for agricultural use. There may be a commercial product available in 2007.

It is likely that there will be an organically-approved boric acid-based bait in addition to conventional bait. Daane and others are also working to establish parasites that will help reduce VMB populations to similar levels of resident mealybugs. Mating disruption with pheromone is also under investigation.

Although more foliar insecticides, insect growth regulators (IGR), and systemic chemigation materials will be used in VMB-infested vineyards than in pre-VMB days, hopefully we will also become more aware of the resident predators and use them to our advantage by developing IPM programs for VMB that effectively utilize chemical tools while conserving the beneficials.

For example, a dedicated IPM or organic grower who has mealybug destroyer beetles (Cryptolaemus sp.) working effectively on mealybug may not want to use the soft insecticide Applaud in the North Coast since it is an IGR and therefore prevents immature insects, including the mealybug destroyer, from developing into adults. The recommended timing of Applaud for the late spring or early summer in the North Coast coincides with the juvenile stage of the beetle, and according to UC IPM Guidelines, may compromise its populations.

Devin Carroll, past-president of the Association of Applied IPM Ecologists (AAIE), has posted a list of grape mealybug natural enemies on the AAIE website, www.aaie.net. The most important are parasitic wasps in the family Encyrtidae, and the predaceous gall midge, Dicrodiplosis californica. Also on the list are mealybug destroyer beetles, lacewings (Chrysopidae), some spiders, earwigs (Forficulidae), and carpet beetles (Dermestidae). Ground beetles (Carabidae) and a minute pirate bug, Dufouriellus ater, are also associated with mealybug colonies but have not been observed attacking them.

Many people find it remarkable that earwigs are omnivorous (feed on more than plant material), but they are well-known to grapegrowers with hand lenses as predators and have been observed eating mealybugs.

Predaceous maggots of the gall midge, and carpet beetles are also among the amazing-but-true beneficials working quietly in vineyards.

Another aspect of VMB management that I have not seen emphasized very widely is deterring birds. We are meticulous about making sure crews and equipment are clean before leaving a VMB-infested vineyard, but allow birds free access to feed in the infested clusters where they can become contaminated with VMB, and then move at will to neighboring blocks and vineyards, spreading the pest to new sites.

Riparian areas, large trees and roosting locations such as power lines, complicate the control of birds moving in and out of vineyards all season long, always with the potential to spread mealybugs. Such areas are good spots to monitor for initial infestations. For growers with an infestation or near an infestation, employing bird deterrents just before veraison would seem to be a prudent strategy.

The Vine Mealybug Workgroup in Napa and Sonoma Counties, along with implementing a coordinated trapping program, is working on a sniffer-dog program that will allow better detection of VMB in the field by utilizing the outstanding olfactory system of dogs rigorously trained with similar methods to those used by search and rescue or security-detection dogs.

Summary
We have been living with grape mealybug, and obscure mealybug on the North Coast of California for years. Natural predators and occasional intervention with pesticides or ant controls have limited their damage with regard to grape quality or yield.

However, vine mealybug poses a much greater threat, and while treatment practices will continue to evolve, we are developing the tools and knowledge to find, reduce damage, and limit the spread of this new important pest.