The recent introduction of a stable female-like navel orangeworm pheromone for monitoring adult males marks a big step forward in the decades-long effort by researchers to develop an index for determining when the navel orangeworm population in an orchard is large enough that an insecticide application makes sense, economically. So points out Bob Beede University of California Cooperative Extension farm advisor, Emeritus, in last month’s issue of his Pistachio Task List newsletter.
“I consider this feat one of the single greatest achievements in modern IPM history!” he writes. “It not only allows us to monitor adult moth activity before egg production, but it also serves as the foundation for the emerging mating disruption programs for almond and pistachio.”
Beede predicts that the use of mating disruption in both crops will, in time, play a key role in suppressing NOW populations on a regional basis. And, because NOW moths produce fewer eggs when mating is delayed, the sooner this happens, the better, he says.
Mating disruption has significantly reduced populations of Oriental fruit and codling moth within two to three years, Beede notes. As he sees it, when used in conjunction with winter sanitation, mating disruption can begin to break down the reproduction cycle of NOW. That, in turn, should lead to a more manageable in-season treatment program.
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In-season sprays create a pesticide residual which controls NOW in some areas but not in others, Beede explains. “Sole reliance on sprays to protect our crop may never allow us to escape the pesticide treadmill we are presently on,” he says. “Add the problem of getting the spray contractor to your ranch on time to the time needed to cover your field, and you can see that the challenge of controlling NOW may get harder, not easier, if we do not begin implementing some of the new technology.”
In the meantime, Beede continues beating the drum to highlight the importance of effective winter sanitation in limiting NOW damage.
Should this winter remain warm and dry, destruction of residual nuts remaining in the trees and on the ground will be especially critical in breaking the NOW life cycle, he says. Beede advises knocking the mummy nuts onto the ground as soon as possible to maximize exposure to rainfall for decomposition. Sanitation also includes blowing mummies out of the crotches at the head of the tree where the limbs arise from the trunk; blowing and raking the berms clean, and, if necessary, destroying the nuts by disking or flailing with a roller behind.
“This cultural practice breaks the developmental cycle of NOW without the use of pesticides,” Beede says. “It requires a community effort.”
It’s a daunting task. As he explains, their much smaller size and lighter weight makes pistachio nuts more difficult to destroy than almonds or walnuts.
Pistachio nuts resist being sucked up and broken by a flail mower. The high air velocity of some blowers used to clear berms of trash and over-wintering nuts blow some of the nuts into the adjacent row of trees just cleaned. Also, the nuts can get imbedded in cracks in the soil around the base of trees from shaking. Depending on the amount of wear on the rubber guards on the shaker frame, anywhere from a few to several handfuls of nuts may be left at the base of every tree.
End result is a lot more overwintering sites for NOW. And, Beede reports, a single NOW female that survives the winter can produce from 85 to 100 eggs in the spring. “So,” he says, “it doesn’t take very many pistachios left per acre to generate a lot of moths for next year.”