The vine mealybug is the most difficult to control due to its prolificacy. “Populations of this species are much more explosive,” Daane says. “In the Fresno area, they can produce six to eight generations in a year, building up greater numbers and causing more damage in the vineyards.”

By comparison, in a given year, the grape mealybug produces just two generations a year and the obscure mealybug may have three, Daane reports.

“Development of the grape mealybug is very synchronized,” he says. “It tends to grow under the bark on the trunk and spurs of vines before it moves out in a uniform pattern to the leaves and fruit clusters. The vine mealybug can be found throughout the year in every possible stage of life feeding almost anywhere on the vines. At harvest, some might be in the fruit clusters, some underneath the bark and others under the soil surface. This makes it more difficult to time application of the spray when it will be most effective.”

Nymphs of mealybugs can enter a vineyard through a variety of mechanisms – even being blown in on air currents. More commonly, mealybugs can be brought into a vineyard on infested nursery stock or cuttings as well as on machinery, equipment and just about anything else that contacts infested plant parts. Close inspection and cleaning equipment can help prevent or reduce that risk, Daane notes.

“If you’re concerned with the ability of mealybugs to transmit viruses associated with grapevine leafroll disease, there’s nothing in the tool kit that provides high enough level of control needed to eradicate this pest,” Daane says.

To reduce development of resistance to insecticides, Daane recommends rotating among products with different modes of chemical action, using products with the same group number no more than twice a season.

Frequency of treatment depends on an individual grower’s level of tolerance of the pest and vineyard conditions, he notes.

“Vineyard managers must adjust their control tools to fit their vineyard,” Daane says.

For example, a 35- to 40-year-old table grape vineyard with an overhead trellis and wide variation in trunk diameters provides numerous places for mealybugs to hide among cracks and crevices in the bark and a large canopy. In this case, insecticide coverage may be more difficult and several insecticide sprays may be needed for adequate coverage, he explains.

In contrast, a  wine grape vineyard with vines less than 5 years and with less foliage, due to lower rates of fertilizers and irrigation water to produce the desired fruit quality, one application of a neonicotinoid insecticide may provide season-long control of mealybugs, Daane adds.