How to Manage Pests
UC Pest Management Guidelines
Scientific name: Platynota stultana
(Reviewed 10/13, updated 10/13)
In this Guideline:
Description of the pest
Omnivorous leafroller can be a significant pest. The larvae are cream colored with black or brown head capsules and resemble other leafrollers, except that they have white tubercles at the base of each bristle along the top of the abdomen. Omnivorous leafrollers are more common in interior valleys and southern California mountain orchards, especially those next to vineyards, than in orchards in coastal areas or at higher elevations of the Sierra Foothills. Orchards may be invaded by omnivorous leafroller moths that develop on host plants outside the orchard. Infestations are often spotty, making monitoring difficult. They have three to four generations per year.
The adult omnivorous leafroller is bell-shaped with blackish gray snoutlike mouthparts that protrude forward from the head. Forewings are dark rusty brown with a tan tip. Size varies from 0.38 to 0.5 inch (9.7–12.7 mm) long. Omnivorous leafroller larvae overwinter in weeds. In spring, larvae complete their development and moths emerge and lay shinglelike egg masses on leaves, which hatch after about 5 days. The larva does not roll leaves as its name suggests. Instead, it weaves a silk nest between two leaves, a leaf and a fruit, or where two fruit touch.
On pomegranates, the larvae typically carve surface grooves where two fruit touch or where the larvae have tied a leaf to the fruit surface. Often the larvae tunnel into the fruit. If skin penetration occurs, pathogens may become established internally and grow on the arils with no visible, external symptoms. If the fruit is not culled before juicing, the product may be ruined.
Insecticide sprays timed according to degree-day accumulations may be used. Mating disruption can be effective if started in February or early March when moths first fly. A second hanging of dispensers may be needed in late summer. Careful monitoring, including occasional fruit and foliage inspections, is critical to the success of these management tools.
More than 10 species of parasites have been recorded from omnivorous leafroller. However, seldom does mortality from these parasites exceed 10%. Predators such as lacewings, minute pirate bugs and spiders also feed on omnivorous leafroller larvae.
During the first flight, adults oviposit on weed hosts near the orchards, so weed control early in the season reduces the second generation that may cause damage to pomegranate orchards. Manage orchard weeds during late winter. Disc clusters and weeds to bury overwintering larvae living on weeds in ground duff. During dormancy, prune out old fruit and destroy by flailing or shredding.
Organically Acceptable Methods
Applications of Bacillus thuringiensis, spinosad (Entrust), and the use of mating disruption are organically acceptable.
Monitoring and Treatment Decisions
Monitor omnivorous leafroller adults with a minimum of 2 traps per block first placed in orchards at 5 to 6 feet high in the canopy around February 15 to 20. For blocks over 20 acres use an additional 1 trap per 20 acres. Check the traps at least one to two times per week until the first consistent moth catch (the biofix date). A treatment threshold based on trap moth catches has not been established. However, traps can be used to time a pesticide application.
If mating disruption is to be used, place pheromone dispensers out in February to early March or at the biofix. To ensure coverage through the long growing season, a second hanging of dispensers may be needed in the late summer (July). In some orchards, putting dispensers out once in mid-May, before the second generation moth flight begins, can provide control.
Pheromone dispensers will disrupt pheromone trap catches. Several times throughout the season, inspect foliage and fruit for leafrollers and damage to confirm that mating disruption is working. Several moths in traps can be an indication that pheromone disruption is not working.
Timing insecticides using degree-days in pomegranate has not been studied, but should resemble the timings that are used in stone fruits. Apply an insecticide about 700 to 900 degree-days (lower development threshold 48°F, upper threshold 87°F) after the first flight. If applying Bacillus thuringiensis, timing must be precise since Bacillus thuringiensis must be ingested to work and is most effective against small larvae. Bacillus thuringiensis has a short residual, should be applied twice about 7 to 10 days apart, is slow acting, and may not reduce numbers quickly.
Continue monitoring trap catches weekly until the second generation flight, about 1200 degree-days after the first flight in late June, treating 700 to 900 degree-days after the first flight.
The third generation, in late July or early August, is most damaging to fruit. If earlier control measures were adequate, additional third generation measures should not be necessary, but if pheromone traps or fruit inspections indicate a continuing problem, additional sprays can be aimed at the third moth flight 700 to 900 degree-days after the flight begins.
UC IPM Pest Management Guidelines:
Insects and mites
D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgments for contributions to Insects and Mites:E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier