Managing the Peach Twig Borer Adds to NOW and Ant Problems
Before the arrival of the navel orangeworm (NOW) in the 1940s, the peach twig borer (PTB) caused the most damage to almond nutmeats. Researchers have discovered a relationship between the two insects: nuts attacked by PTB are favored over sound nuts by NOW. Subsequently, the damage from PTB can be masked by NOW feeding.
The female PTB lays eggs on twigs, fruit, and leaves. The larvae are small, brown caterpillars with white intersegmental bands and a black head capsule. Overwintering larvae are sheltered in tiny cells (hibernacula) that they bore under the bark of limb crotches on one to four-year-old wood or in bark cracks on larger limbs and the trunk. The larvae damage both growing shoots and nuts, causing shallow channels and surface grooves on the nutmeat.
Peach twig borer management
Research conducted by UC specialists and supported by the Almond Board has determined that the peach twig borer can be successfully managed with reduced risk insecticides such as spinosad (Entrust, Success), diflubenzuron (Dimilin), Bacillus thuringiensis, and methoxyfenozide (Intrepid). Dormant treatments with organophosphate insecticides should be avoided because of their potential to create negative impacts on water quality.
Use past history or harvest samples to determine if your orchard will require treatment. Preferred treatment timing is at full bloom and petal fall. Avoid applications of organophosphates during the dormant season as these applications threaten water quality when they run off during winter rainfall. At the beginning of bloom, monitor hibernacula to determine when larvae are emerging. Place pheromone traps out around April 1, and monitor for shoot strikes to catch any in-season problems.
California’s almond growers have substantially reduced the use of organophosphate dormant sprays for control of insects such as peach twig borer and mites, thanks to studies supported since 1998 by the Almond Board with additional funding from state and federal agencies. Numerous UC researchers and farm advisors have played a role in the studies, which show that best management practices can reduce the use of dormant sprays, and that newly-available reduced-risk materials applied either in-season and/or in combination with a dormant oil application can control peach twig borer and other insects and mites. Treatments during the dormant season with environmentally sound insecticides such as spinosad (Entrust, Success) and diflubenzuron (Dimilin) are acceptable.
Dormant Spray Alternatives
UC IPM Pest Management Guidelines
Seasonal Guide to Environmentally Responsible Pest Management Practices in Almonds