First becoming a problem for pistachio growers just around Tulare, Calif., more than a decade ago, Gill’s mealybug has spread throughout Tulare County and is now moving into northern Kern County.

David Haviland, University of California Extension farm advisor for Kern County, warns pistachio growers — be wary of Gill’s mealybug.

“Gill’s mealybug reproduces very quickly in the summer, feeding on the nut hull and pulling out plant juices, carbohydrates and other nutrients intended for development of the pistachio kernel,” he says. “So, you end up with smaller kernels, lower yields, more closed shells and more staining.”

That’s not all, the feeding insect produce of large amounts of honeydew, which supports growth of black sooty moldon the leaves that can reduce photosynthesis.

Once the insect infests an orchard, it requires annual control, Haviland notes.

He recommends starting a control program in May by scouting the orchard for the 2- to 5-mm long, pinkish gray adult females.  “Look at the base of the nut cluster,” he says. “If you find at least one female in every eight or nine cluster, you’ll need to treat the trees.”

One research project showed that an average of three Gill’s mealybugs per cluster in May can reduce the value of harvested the crop by 15 percent.

The best time to spray in the southern San Joaquin Valley is in early June, Haviland says. By then, the crawlers produced by the adults have reached the first instar stage and the nymphs are most susceptible to insecticides. That’s also when the foliage still allows for good spray coverage.

Insecticide choices include Admire, Assail, Centaur and Movento.

“One application should control Gill’s mealybug for one season and, sometimes, two,” Haviland says.

The key to preventing spread of this pest is sanitation. He advises washing harvest equipment before it moves from one orchard to another. “Requiring equipment be cleaned before it arrives in your fields should be part of your contract with the harvester,” Haviland says.