Winter sanitation and ground management practices for navel orangeworm (Lepidoptera: Pyralidae) control in pistachios

The navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is a key pest of California nut crops, whose control programs include the winter sanitation of unharvested nuts (mummies). A 5-yr survey of pistachio orchards showed a positive association between the number of mummies per tree and the number of A. transitella eggs deposited during the first flight in 3 of 5 yr, and a negative association in 1 of 5 yr. Factors that impacted overwintering A. transitella included the number of closed or empty nuts lacking a kernel (blanks), infestation levels (range 0.4% to 13.5%), and the number of mummies on the ground (range 11.2 to 90.6 mummies per m2). There was higher moth emergence from nuts on the berm than from the row middles. Mowing, discing, or rototilling the row middles reduced adult moth emergence, with raking nuts into the row middle being the most effective. Neonate A. transitella utilized both open pistachio mummies and insect damaged or split mummies; closed shell mummies and new crop undamaged nuts were not used. Oviposition varied by egg trap location, with the fewest eggs deposited on ground traps, and similar numbers deposited at mid-canopy and at upper canopy. These findings underscore the importance of winter sanitation that includes destroying ground mummies in pistachios to reduce the standing population of A. transitella and that a complete program includes both the removal of mummies from the canopy as well as their subsequent destruction on the ground.