Peach twig borer is a major pest in several tree crops, including almonds. The larvae damage growing shoots and nuts, causing shallow channels and surface grooves on the nutmeat. Peach twig borer damage can be masked by navel orangeworm feeding, which often occurs on nuts previously damaged by peach twig borer.

Not every orchard requires treatment to control peach twig borer. Even if yours does, you may not have applied a Bt spray during bloom to control overwintering larvae due to concerns about the effects of some insect growth regulators on bee health. In that case, Gurreet Brar, University of California Cooperative Extension farm advisor for Fresno and Madera Counties offers an alternative – treat your trees in May with an organophosphate or IGR spray.

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The timing of this treatment is based on flight activity, as determined by the use of pheromone traps and degree-day calculations.

Start by setting up the pheromone traps in your orchard by April 1. Place at least two traps per block, spacing them uniformly throughout the orchard and at least five trees in from the edges.  Hang the traps in shade in the northern quadrant of the tree at a height of 6 to 8 feet above the ground and 1 to 3 feet inside the tree canopy.

Check the traps twice a week until you catch the first adult moth. Then, check them weekly. The date you first catch two moths in the same trap is biofix. Time your spray application to coincide with the first flight of the moths, as determined by the number of degree-days after biofix. For organophosphate insecticides the optimum timing for the May spray is 400 to 500 degree-days after biofix. If you’re treating with an IGR, apply it 300 to 400 degree-days after the first male moth is trapped in April.

You can record your trap catch using a pheromone trap and degree-days form, which is available online.

University of California Pest Management Guidelines for almonds point out that, if navel orangeworm is also a problem, you may be able to time the May peach twig borer spray to control both pests. That is, if the navel orangeworm egg hatch occurs at about the same time as the optimum time for the peach twig borer spray. If not, wait and spray the navel orangeworm at hull split and time the May spray for peach twig borer. Keep in mind that control of peach twig borer during hull split is difficult.

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