How to Manage Pests
UC Pest Management Guidelines
Scientific name: Amyelois transitella
(Reviewed 2/07, updated 2/09)
In this Guideline:
DESCRIPTION OF THE PEST
Young worms are reddish orange and later appear cream colored, although their diet can influence coloration. They have a crescent-shaped sclerite on each side of the second body segment behind the head. As the worm matures, the head becomes reddish brown. Adult moths are about an inch long, have predominately gray forewings with black markings, and a snoutlike projection at the front of the head. Females begin egg laying about 2 nights after emergence. Eggs are laid on mummy nuts or on new crop nuts.
The navel orangeworm feeds on a variety of fruits and nuts and is the most damaging caterpillar in pistachio. Almonds, figs, pomegranates, and walnuts are also major hosts. The pistachio nut is susceptible to infestation as soon as hull split occurs. The first signs of an infestation are small, pinhole-size entrances into the nutmeat. As worms grow in size, the entire nut is fed upon and extensive amounts of webbing and frass are present. Infested pistachios will split early and can usually be seen by mid-July.
Navel orangeworm is managed by the removal of unharvested nuts in fall as well as the destruction of any nuts left on the soil surface. Insecticide sprays aimed at the third generation eggs and early harvest are also components of a good management program.
There are several parasites such as Goniozus legneri and Copidosomopsis plethorica that can reduce damage from navel orangeworm. Goniozus legneri is commercially available for release and serves as an alternative control in organically managed orchards.
Navel orangeworm is a scavenger pest that survives from one season to the next on unharvested nuts left on the tree or on the ground. Because infestations of citrus flat mite and mealybugs can increase the number of nuts remaining on the tree after harvest, good management of these pests is necessary for good navel orangeworm management.
In almonds it has been demonstrated that the removal and destruction of nuts that remain on the tree after harvest can dramatically reduce infestations in the next crop. Removal and destruction of these nuts is also critical in pistachio for navel orangeworm control. Although early nut harvest is more difficult to accomplish in pistachio orchards, harvest nuts as soon as possible to reduce exposure to egg-laying female moths.
Nuts on the orchard floor should also be destroyed because navel orangeworms have been found surviving, during the summer months, on last season's nuts left on the orchard floor. Recent studies of winter sanitation practices for pistachio, including discing mummies on the orchard floor, however, have found them to be more costly and less effective than in almond orchards.
Organically Acceptable Methods
Biological and cultural controls are acceptable for use on organically certified crops, including releases of the parasite Goniozus legneri and sprays of the Entrust formulation of spinosad.
Monitoring and Treatment Decisions
Calculate degree-days for navel orangeworm in your location.
Learn to use degree-days to time insecticide applications.
Generally only the third generation of navel orangeworm is treated in pistachio; timing of this treatment is critical because once the worm is in the nut, it cannot be controlled with insecticides. Use egg traps baited with a mixture of pressed almond meal and almond oil (3 to 5%) and degree-day calculations to time the treatment.
Hang traps in the orchard in spring and check twice a week for egg-laying activity. Use a minimum of four traps per block. Egg-laying peaks will be observed in May and from late June to early July, signaling the first and second generations. If navel orangeworm populations are low during the first two generations, add another trap to each of the four trapping locations to increase trapping effectiveness. During late July examine the traps every 2 days. If egg laying increases on two consecutive readings, this signals the beginning of the laying of third generation eggs. Begin degree-day calculations when the first increase of third generation egg deposition is noted. Use a lower threshold of 55°F and an upper threshold of 94°F". Spray at 400 degree-days from the beginning of third-generation egg laying. If a large amount of acreage must be covered, begin to spray at 300 degree-days.
UC IPM Pest Management Guidelines:
Insects and Mites
Acknowledgment for contributions to Insects and Mites: