Pest Control Advisor Larry Whitted and organic grower Jay Leone examine a grapevine leaf for parasitized mealybugs in Leone's Lodi vineyard during the Lodi Winegrape Commission's mealybug biocontrol field day. Photo: Ted Rieger.

Lodi, Calif.—Management of vine mealybug (Planococcus ficus) in California vineyards has been problematic because of this pest’s high reproduction potential with multiple generations, and its year-round presence with life stages that overwinter under vine bark where it is difficult to apply treatments.

The vine mealybug (VMB) causes damage by feeding on grape clusters and vine parts where it produces honeydew that provides a medium for mold growth, and makes grapes unmarketable. In addition, the VMB is a vector of grapevine leafroll-associated viruses.

When the VMB became an issue in California vineyards in the 1990s, common advice was to use strong insecticides, such as Lorsban (chlorpyrifos) to eliminate the pest. In some cases, this later led to more mite and leafhopper problems as beneficial predators of those pests were also killed. Over time, other chemicals and control methods became available.

Now growers are taking a more integrated approach to VMB control.

The Lodi Winegrape Commission’s (LWC) recently formed the Mealybug Biocontrol Research Focus Group, which held a field day Aug. 8 to educate growers in field identification and management of the VMB, and the identification of parasitized mealybugs and insects that are effective mealybug predators. LWC research and education director, Dr. Stephanie Bolton, coordinates the focus group’s activities as the principal investigator for a two-year project funded by the American Vineyard Foundation. “A primary objective for the research focus group is to educate growers on what we can do to integrate more biocontrol into our normal integrated pest management (IPM) programs and spraying activities,” Bolton said.

The field day was hosted by organic grower Jay Leone, in a 30-acre block of Cabernet Sauvignon that has a high endemic population of the parasitic wasp (Anagyrus pseudococci). This wasp was imported and introduced into California in 1934 by the citrus industry for control of the citrus mealybug. Releases of the wasp have also been made in California vineyards for VMB control, and it has established populations in many vineyard regions. Other wasp species are found in California that are VMB parasitoids, but A. pseudococci is the dominant parasitoid throughout the state.

Leone is advised by Lodi area consultant Larry Whitted, a licensed pest control adviser (PCA) and a certified crop adviser (CCA). In 2016, Whitted discovered an unusually high level of VMB biocontrol occurring in Leone’s vineyard. Although many vine trunks were wet with colonies of VMB under the bark, as the VMB moved off the trunk to leaves, they were heavily parasitized by the Anagyrus wasp. Whitted also found significant VMB parasitism by the wasps in other vineyards in Lodi and Clarksburg. Whitted invited UC Cooperative Extension specialist Dr. Kent Daane, a research entomologist that has studied VMB in California since its arrival in the 1990s, to Leone’s vineyard to confirm his observations.

Speaking at the field day, Daane said, “Last year, I couldn’t find any live mealybugs in leaves or fruit, and this vineyard had one of the highest degrees of parasitism I have ever seen.”

Leone’s vineyard is more than 20 years old and was originally farmed conventionally. Leone bought the vineyard seven years ago and converted it to organic production. The vines had minimal powdery mildew this year and no sprays were applied. Many of the vines show Eutypa dieback symptoms, a common issue in older Cabernet vines, but the vineyard still produces 3 tons per acre. With the high populations of parasitic wasps, the VMB is kept in check, mostly confined to lower portions of the vine without causing fruit damage. No leafroll virus problems have been identified in the vineyard to date.

At the field day, attendees took loupe style magnifying hand lenses and walked the vineyard to look for signs of VMBs and parasitic wasps, commonly found on the undersides of grape leaves. Healthy VMBs appear flat, whereas parasitized VMBs can appear puffy and yellow. The female wasp oviposits an egg in the VMB host, either an adult or a nymph. As the wasp larva develops, the VMB host becomes immobilized in about one week and is then mummified. The adult wasps emerge from an exit hole in the mummified VMB in about two to three weeks. As Whitted explained, “If you see an exit hole in the VMB, you know it was parasitized.”

Attendees were encouraged to look for parasitized mealybugs in their own vineyards and report finds to the LWC to track the distribution and spread of beneficial insects in the Lodi region.

'Don’t kill the good insects'
The LWC research focus group is educating growers to integrate biocontrol into their VMB management. The first step, as Bolton emphasized, “Don’t kill the good insects!”

In addition to Anagyrus wasps, other VMB predators include Cryptolaemus montrouzieri, a type of lady beetle also called the mealybug destroyer, and lacewings. Both of these predators are found in Leone’s vineyard and in the Lodi region. Anagyrus wasps and lacewings also prey upon leafhoppers. Beneficial insects found in Lodi vineyards that control mites are six-spotted thrips, minute pirate bugs and predatory mites. Parasitic wasps and flies can control caterpillars and omnivorous leafrollers.

Daane also mentioned predaceous midge flies in the family Cecicomyiidae are found in some California vineyards that can feed on mealybug eggs and larvae.

To assist growers, the LWC focus group produced and distributed a chart based on the “UC-IPM Relative Toxicities of Insecticides and Miticides Used in Grapes to Natural Enemies and Honey Bees Table.” The LWC’s simplified table lists the major pesticides registered in California for use in grapes based on their potential effects on beneficial insects divided into three categories: “Good insects stay alive,” “May reduce good insects,” and “Good insects are killed.” The chart is available at the LWC website.

Growers have found Movento (spirotetramat) to be good for VMB control while also being safe for beneficial predators. However, there is concern about the VMB developing resistance over time to Movento. Movento is sometimes rotated with neonicotinoid pesticides, such as Admire Pro (imidacloprid), safe for beneficial insects when used in a soil (dripline) application.

Control timing and mating disruption
Daane emphasized the importance of timing in controlling VMB, related to pesticide applications. The VMB overwinters under bark in the vine trunk and on vine roots underground. VMBs start to move up the vine in spring as temperature increases, vine growth begins, and populations increase. The VMB can produce up to six generations during the growing season in Lodi, and population density increases until harvest. Movento is applied as a foliar treatment taken into the leaves to kill VMBs after feeding. “You want Movento taken up into the vine before the VMBs begin moving up from the trunk,” Daane advised.

Suterra, a supplier of biocontrol products for insect control based in Bend, Oregon, first introduced VMB pheromone dispensers (CheckMate VMB-XL) to place in vineyards for mating disruption. The dispensers are placed once per season in the vineyard, timed to coincide with the first significant male VMB flight in May-June, at a rate of 250 per acre.

Suterra more recently introduced a sprayable pheromone product “CheckMate VMB-F” that is more economical to buy and apply by being sprayed on vine foliage. In many cases, it can be applied in combination with regular insecticide or fungicide applications. This product creates more point sources that attract male VMBs and make it more difficult for them to find the female VMBs. Spray applications are recommended at monthly intervals from about late May to early October, depending on location and temperatures that affect VMB development. Mating disruption tends to be more effective when VMB populations are at lower levels.

Daane said mating disruption can also help with biocontrol. “We think we get increased VMB parasitism when mating disruption is used, because we think the pheromone is attracting Anagyrus, and it keeps the wasps in the area searching for VMBs,” he said.

Ant control
Some ant species, such as Argentine ants, feed on the sticky, sugary honeydew created on vine parts from VMB feeding activity, and they will protect and tend mealybugs for this reason. When ants are present, ant control must be part of a management program to allow the insect predators to access the VMBs.
Focus group activities

The 11-member LWC focus group meets once a month to plan and implement objectives. The group plans to determine which mealybug biocontrol agents are providing control in the region and educate growers on how to keep existing populations of beneficial insects alive and healthy. The group is working with California biocontrol insectaries to look at cost-effective methods to increase local parasitic wasp populations and the possible use of wasp releases in the area.

Joe Barcinas, manager of Foothill Agricultural Research Insectary in Corona, Calif., visited Lodi and collected samples of wasp specimens from the Leone Vineyard for possible use as breeding stock at his insectary. The focus group intends to formulate a long-term management plan to establish economically feasible and impactful mealybug biocontrol.