This year’s warmer weather is also adding to the increased NOW threat. Many areas of the San Joaquin Valley have accumulated more degree-days so far this year compared to last season.

“Heat units are the fuel which drives development of navel orangeworm,” Siegel says. “With more heat units, you get a larger population of the insect earlier in the season.”

Two other factors favor more NOW numbers in the spring. In almonds, winter drought has caused insect-harboring mummies to stick tighter to trees. Stick-tights are more difficult to shake loose and some growers may have relaxed their winter sanitation practices, Siegel suggests.

For pistachios, there’s the trend to more two-shake harvests as growers glean as many nuts as possible to make the most of current high prices. “About 70 percent of the industry has gone to double-shaking pistachios,” Siegel explains. “Consequently, pistachios are staying on the trees longer into October for a second shake, and that’s when navel orangeworm populations are high already. So, even in years of normal navel orangeworm levels, it’s becoming inherently more of challenge to protect the nuts.”

In the meantime, Siegel is recommending that almond growers facing more pressure from the pest than usual this year, consider moving up their peach twig borer (PTB) insecticide spray using an insecticide with activity against both peach twig borer and NOW. 

Growers facing high pressure also might benefit from an extra NOW treatment after hull split treatment (hull split and post hull split spray), he notes.

“I like to treat for navel orangeworm at 1 percent hull split to see if I can knock down the population earlier,” he says. “Regardless of your management practices, the high navel orangeworm populations this year call for doing more than you’re used to in order to control this pest.”

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