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Researchers waging multi-front battle to control vine mealybug

California researchers are developing a comprehensive strategy for controlling vine mealybug in California vineyards that includes insecticides, vineyard sanitation, biological control and mating disruption.

Unlike its cousin, the grape mealybug, vine mealybug is not a native pest to California grapevines. While the grape mealybug has been around as long as grapes have been in the ground in California, the vine mealybug was first found in Coachella Valley vineyards in 1994 and has since spread throughout the state to most grape producing regions. Seven California counties are now fully infested with vine mealybug, and another 10 have reported positive finds of the insect.

“This insect is becoming one of the key pests in California these days,” said Kent Daane, University of California Cooperative Extension insect biologist at the recent San Joaquin Valley Grape Symposium in Easton, Calif. Based at Kearny Ag Center in Parlier, Calif. Daane is working on integrated methods of control for vine mealybug.

The University of California Cooperative Extension put on the meeting. It was sponsored by the California Raisin Marketing Board.

Vine mealybugs can become quickly established and are spread easily from one area to another on wind, by field crews, and even on animals like rats and birds.

The insects damage grape crops by feeding on leaves throughout the summer and secreting honeydew that contaminates clusters. It can also vector viruses, which makes control of even low populations more important, Daane said.

“They produce multiple generations in a season, which means that growers need to take immediate action to slow population growth down.”

Daane said a first step to prevent spread of vine mealybug is to practice good sanitation to keep the insects from moving from one location to the next on the clothes of field crews and harvesting equipment.

“The best tool is to use a high volume water sprayer to wash harvesting equipment down.”

Traditional insecticides are key to vine mealybug control, but Daane is working to develop an integrated program that can reduce grape growers' reliance on a few broad-spectrum insecticides.

Daane said broad-spectrum products such as Lorsban and Lannate work best at knocking back insects and providing long residual control. Use of these products has increased in vineyards since 1994 as growers struggle to contain VMB, and Daane is concerned that future regulatory action could reduce or eliminate the availability of these products. Growers therefore need to use them judiciously to keep overall use rates level and retain those registrations for integrated management programs.

“We want to make sure we are using these pesticides judiciously and only when needed. If we can keep their use flatlined and use them only as needed, we have a better chance of keeping those materials.”

Additional insecticides have proven effective, including dimethoate, Applaud, Assail, and either imidacloprid or Venom, depending on soil type. A new product called Movento is also being introduced that has performed well in trials. Daane noted that these products don't have the quick knockdown growers get from broader spectrum insecticides.

In his trials, a delayed dormant application of chlorpyrifos (Lorsban) still worked best at targeting peak population levels with up to three weeks of residual control.

“You want to put it on as late as possible at a time when you get the most activity, but it's got to be a dormant application because you don't want to put it on at bud break,” he said.

To complement insecticides, Daane said biologicals are also an important component in an integrated management program. Native VMB parasitoids such as Anagryus pseudococci and Leptomastix dactylopii can provide excellent parasitism, but often miss vine mealybug pests hidden in the cracks and crevices of the vine, and don't work well throughout the season.

“We're getting great control, but parasitism comes at the peak in September. We want to kill those vine mealybugs before they get to clusters, so parasitoids may come too late for total control,” he said.

Daane is currently seeking out new parasites in other areas of the world that he hopes will more aggressively attack hidden VMB pests and be better adapted to California climate conditions to improve parasitism rates.

Daane is also exploring the use of pheromone mating disruption to complement a single application of insecticides such as imidacloprid or buprofezin in vine mealybug control programs. He is in the middle of a three-year replicated trial using a new VMB pheromone to reduce the number of generations in a season.

“So far we are very pleased with the results. We're taking our test vineyard that was 20 percent to 40 percent infested and knocking those numbers way down.”

Daane is currently working with the California Department of Pesticide Regulation to secure a Section 18 emergency registration for the pheromone on grapes, though he said it would likely only initially be for raisins, since those emergency exemptions are based on profit losses for a single pest.

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