“Perhaps 100,000 acres have mealybug today,” Haviland said.

Gill’s mealybugs are roughly ½ to 1/5 inch in length and pinkish grey in color. The pest is often covered with white wax secreted from a pore.

“They muck up the clusters,” Haviland said.

He explained that they “intercept carbohydrates intended for kernel development.”

Smaller kernels mean less weight and less splitting.

“The small kernel is never big enough to push them open,” Haviland said, “and the biggest problem is closed shell nuts.”

The pest can cause shell staining and an increase in adhering hulls with later harvests. But it has no association with aflatoxin.

Pistachio growers should be cautious not to confuse Gill’s mealybug with grape mealybug.

Grape mealybug is sometimes found on pistachios, but does not cause economic damage but requires treatment. Grape mealybug has four slender white tails. The female Gill’s mealybug has two broad white tails.

When poked, adult females of grape mealybug extrude a bright red liquid through structures called ostioles towards both the rear and front of the top of the body. Gill’s mealybug does not extrude such a liquid.

Mealybug feeding produces large amounts of honeydew that results in black sooty mold that can reduce photosynthesis.

The most common predators of mealybugs in pistachios are brown lacewing and lady beetle whose larva resembles a mealybug.

One way to peg problem areas is to check trees before dormancy in the fall and look for sooty mold and leaves and for mealybugs within clusters. Note those locations for further evaluation the following spring.