A second-year-in-a-row blowup of navel orangeworm in California almond and pistachios could be coming.

Conditions similar to those that contributed to last year’s navel orangeworm (NOW) population explosions — a dry winter and warm spring — are being repeated in 2013.

“This season navel orangeworm levels look as potentially damaging as 2012,” says entomologist Joel Siegel, with the USDA’s San Joaquin Valley Agricultural Sciences Center, Parlier, Calif.

Last year NOW damage varied across the state. Tulare County pistachio orchards were hit particularly hard. Populations skyrocketed early in the harvest and stayed until the end.

“On the very first day, loads were coming in with as much as 4 percent navel orangeworm damage,” Siegel says. “In a normal year, you may get a fluke load like that early in the season. But, then it subsides. Last year, insect damage in Tulare County remained high throughout the harvest.”

In other areas, like Kern County, the low levels of NOW damage in pistachio orchards at the beginning of harvest rose as the harvest progressed.

As much as 15 percent of Nonpareil almond loads in Madera county orchards suffered damage from the feeding worms, Siegel notes.

Like 2012, almond and pistachio orchards started this season with already-high populations of overwintering NOW. In some instances, the numbers were very high.

Brad Higbee, research entomologist with Paramount Farms, reports egg counts totaling 8,000 per trap in Kern County, Siegel says.

“Up to then, the most he had seen in a trap was around 1,400,” Siegel says. “Many growers have never seen more than 300 eggs in a single trap.”

One reason for the high early-season numbers is limited winter rainfall both this year and last season.

“The key period for navel orangeworm mortality is from mid-December through mid-February, which usually coincides with winter rains,” he says. “But, we haven’t had those rains the last two winters. That has resulted in the much higher survival rates.”