How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Omnivorous leafroller is primarily a pest of peaches in the San Joaquin Valley. It occurs in the Sacramento Valley but seldom causes damage. Omnivorous leafroller overwinters as immature larvae in mummy fruit or on winter weeds and does not enter dormancy. Larvae are light colored 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. They pupate inside a webbed shelter.

Adults of the overwintering generation emerge by March 1. They are small, dark brown moths, 0.5 to 0.375 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 that hatch from this generation of eggs can cause significant damage in stone fruits. Like fruittree leafroller and obliquebanded leafroller, they have the characteristic behavior of wriggling backward when disturbed and dropping from a silk thread attached to the leaf or fruit surface.

DAMAGE

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, and webbing is usually present on fruit.

Primary damage results from fruit feeding. Young fruit may be destroyed, and scars on older fruit will cause them to be culled or downgraded at harvest. Feeding injury also may increase the incidence of brown rot and other fruit decays.

MANAGEMENT

Omnivorous leafrollers do not usually appear in peach trees until early summer. Regular monitoring each season is important so that prompt action can be taken if damaging populations develop. Throughout the season, watch for the presence of leafrollers while monitoring.

Biological Control
A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack omnivorous leafroller larvae. General predators such as lacewings, Phytocoris bugs, 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 pesticides that are least disruptive of biological control when treating other pests.

Cultural Control
Remove and destroy fruit mummies; also destroy potential overwintering weed hosts, such as horseweed, common lambsquarters, little mallow, curly dock, and legumes, by clean cultivation.

Organically Acceptable Methods
Biological and cultural control along with applications of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable tools.

Monitoring and Treatment Decisions   Degree-day calculator    Degree-day table
Begin monitoring by placing pheromone monitoring traps in the orchard by February 20 in the San Joaquin Valley and check twice weeklyto establish the biofix for the first flight; biofix is the first night moths are consistently caught in traps over a period of several nights (see PHEROMONE TRAPS). 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 for all but the earliest varieties.

From the first biofix, accumulate degree-days (DD) to estimate when the onset of the second flight will occur. Use a lower threshold of 48°F and an upper threshold of 87°F. (For assistance in calculating degree-days, see "Degree-days.") 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.

Take fruit samples every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program (see FRUIT EVALUATION AT HARVEST). Record results on monitoring forms for preharvest (112KB, PDF) and harvest (116KB, PDF) samples.

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PUBLICATION

UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
Insects and Mites
C. Pickel, UC IPM Program, Sutter/Yuba counties
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
K. R. Day, UC Cooperative Extension, Tulare Co.
Acknowledgment for contributions to the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier

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