As walnut harvest nears, the one remaining insect threat to the crop is navel orangeworm. Although the third flight is now under way in many areas, some orchards may experience a fourth flight.
Walt Bentley, IPM entomologist with the University of California at Kearney Agricultural Center at Parlier, points out that the moths can move among different species of orchards to lay eggs in nuts hanging on walnut, almond and pistachio orchards.
They don’t lay eggs in nuts lying on the ground, which is why he advises walnut growers to drop nuts as soon as they are ready for harvest.
“Once they’re ready, get them off the trees and picked up as quickly as possible,” he says. “The longer the nuts are exposed on the trees, the greater the potential for infestations.”
This is especially critical in walnut orchards adjacent to pistachio orchards, which typically harbor a higher population of NOW. As a result, the risk of the moths moving from pistachios to walnuts is greater than movement in the opposite direction.
Whether you use your own harvesting equipment or hire custom operators to shake the trees, the key to controlling NOW at this point in the season, Bentley says, is to plan ahead. Schedule each block for shaking to minimize any delay once the nuts are mature.
By now, any spider mites present in an orchard pose little or no threat to walnuts, Bentley says. “Populations of these mites tend to drop in August. Unless you see webbing you can ignore any spider mites you see at the end of the August — they are no longer a cause for concern this season.”