Controlling the Navel Orangeworm (NOW) in California almond orchards is easier and more effective with proper winter sanitation than a perfectly-timed spray program.

The benefits of cultural practices, winter sanitation and insecticide treatments are significant, according to Walter Bentley, University of California, Davis integrated pest management entomologist Emeritus.

Bentley told about 150 almond producers and industry members at the Southern San Joaquin Valley Almond Symposium held in Kerman, Calif. in June that even the best-timed May spray program will control about half of all NOWs in an orchard.

Proper winter sanitation efforts can increase NOW eradication efficacy to as high as 80 percent.

“When talking about May sprays and Navel orangeworm management, we’re really not talking about protecting this year’s crop,” Bentley said.

“Navel Orangeworm cannot get into a nut until the hull splits. So when spraying in May, the grower is managing the larvae on last year’s un-harvested crop (mummies in the tree).”

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While Bentley cautioned growers against looking primarily at well-timed spray applications to protect nuts, he did not entirely discount properly timed insecticide programs as an effective management tool.

“I’m not saying that May sprays aren’t of value; they certainly are. If the growers does a good job of (winter) sanitation and there is not the movement of moths from other sites, you may be wasting money with a May spray.”

Winter sanitation is particularly critical in the central and southern San Joaquin Valley (SJV) where NOW appears to have a stronger foothold in almonds.

A better management plan for NOW control in almonds, Bentley says, is the effective removal and destruction of mummy nuts during the fall and winter months, coupled with the harvest of nuts as soon as possible.

A key to remember, Bentley stressed, is that the Navel orangeworm cannot get into the almond nut – the place it feeds – until after hull split, which usually happens in June.

Prior to that, a good insecticide treatment program can be effective for NOW control, particularly in orchards where winter sanitation efforts and a quick and timely harvest of last year’s almond crop were not carried out effectively.

Bentley recognizes that NOW infestations, regionally speaking, have been more severe in the southern SJV county of Kern, with less pest pressures visible in the Sacramento Valley or even the northern SJV.

“For many, many years, Kern County has faced more severe Navel orangeworm pressure,” Bentley says. “I think this is due to (poor) winter mortality.”

Even so, Bentley praised the stepped-up efforts of Kern County almond growers over the past several years with respect to early harvest and winter sanitation efforts.

“They do a tremendous job of sanitation down there,” he said.