Record heat last July and August compounded the problem. The hot weather caused an unusually large number of hulls to shrink and split, allowing the larvae easy access to feed on the nuts.

Regardless of the reason, NOW exacted a heavy toll from growers last year. Processors rejected 1.9 percent of the nuts they received due to damage from the insect. That’s nearly 2 percent of the crop for which growers received no payment.

Pistachio growers can earn a premium based on the quality of their nuts. Paramount pays growers a bonus of as much as 10 cents a pound for top-quality pistachios. Last year, due to the amount of navel orangeworm damage to the nuts, the bonus averaged 7.5 cents per pound.

“Paramount growers lost an average of $375 an acre or 11 cents a pound from navel orangeworm damage associated costs,” Anzaldo says. “On an industry-wide basis that represents a total loss to growers of about $60 million dollars on last year’s 552-million pound crop.”

Growers who were able to minimize NOW damage in 2012 were those following a fully integrated pest management program, he adds.

That includes:

• Setting out traps to monitor navel orangeworm numbers and determine when treatment is warranted;

• Rotating insecticide materials among different chemistries to reduce build-up of NOW resistance;

• Combining ground sprays with aerial applications to improve spray coverage of the tree canopies;

• Harvesting the nuts as soon as they are ready to minimize exposure to egg-laying females;

• Winter sanitation of the orchard to destroy mummies nuts left on the ground which harbor over-wintering navel orangeworm larvae.

“Growers who took all of these steps last year had much less navel orangeworm damage in their orchards than those who didn’t,” Anzaldo says. “All these practices are necessary, if the industry is going to maintain its reputation for producing high quality pistachios.”