How to Manage Pests
UC Pest Management Guidelines
Scientific name: Platynota stultana
(Reviewed 8/06, updated 3/09, pesticides updated 10/15)
In this Guideline:
DESCRIPTION OF THE PEST
Omnivorous leafroller larvae are light-colored caterpillars with dark brown or black heads. When mature, they are about 0.6 inch (1.5 cm) long and have two slightly raised, oblong, whitish spots on the upper surface of each abdominal segment. Abdominal segments may have a greenish brown tinge. Larvae pupate inside a webbed shelter. Adults of the overwintering generation emerge in March. They are small, dark brown moths, 0.38 to 0.5 inch (9-12 mm) long with a dark band on the wing and a long snout. Eggs are laid in overlapping rows that resemble fish scales. The first generation of eggs usually is laid on weed hosts, and adults from this generation emerge in May or June to lay eggs in orchards on leaves and fruit. Larvae have the characteristic behavior of wriggling backward when disturbed and dropping from a silk thread attached to the leaf or fruit surface.
This pest has two to four generations per year depending on climatic conditions. 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.
Omnivorous leafroller larvae often web leaves into rolled protective shelters while feeding. They feed on leaves and on the surface of fruit, sometimes webbing one or more leaves to the fruit for protection. They chew shallow holes or grooves in the fruit surface, often near the stem end. The damage is similar to that caused by orange tortrix. Larvae feed where fruit are touching, so entire clusters can be damaged.
Omnivorous leafrollers commonly develop on host plants outside the orchard and move into the orchard in early summer. Infestations often are spotty, making monitoring difficult. Throughout the season, watch for leafrollers when monitoring other pests.
A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack omnivorous leafroller larvae. General predators such as lacewings, Phytocoris, assassin bugs, and minute pirate bugs may feed on eggs and larvae. Preservation of natural enemy populations is an important part of keeping leafroller numbers low. Use selective materials that are least disruptive of biological control when treating other pests.
Organically Acceptable Methods
Biological and cultural control along with applications of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable.
Monitoring and Treatment Decisions
Calculate degree-days for omnivorous leafroller in your location.
Learn to use degree-days to time insecticide applications.
Begin monitoring by placing pheromone monitoring traps in the orchard by mid-February in the San Joaquin Valley to establish the biofix for the first flight; biofix is the first night moths are consistently caught in traps over the period of several nights. First generation omnivorous leafrollers are most likely to appear on weeds or cover crop; treatments for this first brood are probably not necessary and are likely to be ineffective. From the first biofix, accumulate degree-days (DD) to estimate what the onset of the second flight will occur. Use a lower threshold of 48°F and an upper threshold of 87°F. It takes about 1168 DD for omnivorous leafroller to develop from egg to adult. As the start of the second flight nears, be sure to have fresh trap liners and lures in place. When the second flight biofix is determined by trap catches, begin accumulating degree-days. Research in the central San Joaquin Valley indicates that the optimum single treatment timing is between 700 and 900 DD after the start of the flight. Monitor the fruit closely for signs of damage. No treatment threshold values are available.
UC IPM Pest Management Guidelines: Apple
Insects and Mites
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
Acknowledgment for contributions to Insects and Mites:W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
H. L. Andris, UC Cooperative Extension, Fresno County
C. Pickel, UC IPM Program, Sutter/Yuba counties
W. W. Coates, UC Cooperative Extension, San Benito County