Omnivorous Leafroller

Omnivorous leafroller is primarily a pest of nectarines 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 a true dormancy. Larvae are light colored with dark brown or black heads. When mature they are about 0.6 inch 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 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, but can also be found on early maturing nectarine cultivars causing moderate damage. Adults from this generation emerge in May or June to lay second generation eggs in orchards on leaves and fruit. Larvae that hatch from this second generation of eggs can cause 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.

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.

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.

Omnivorous leafrollers can be found in orchards in the spring, but the majority of damage occurs during the 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 leafroller larvae while monitoring.

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.

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.

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

Begin monitoring by placing pheromone monitoring traps in the orchard by February 20 in the San Joaquin Valley and check twice weekly to establish the biofix for the first flight (overwintering generation), which should occur around March 1; biofix is the first night moths are consistently caught in traps over a period of several nights, see PHEROMONE TRAPS. From the first biofix, accumulate degree-days (DD) to estimate when to apply a treatment. Use a lower threshold of 48°F and an upper threshold of 87°F. Optimum treatment timing is between 700 and 900 DD after the first biofix.

Estimate the onset of the second flight (first generation adults) by accumulating degree days from the first biofix. The second flight begins approximately 1168 DD after the first biofix, because this is how long it takes the 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. If necessary, apply an insecticide for the second larval generation between 700 and 900 DD after the start of the second flight biofix. Monitor the fruit closely for signs of damage. No treatment threshold values are available.

Calculate degree-days for omnivorus leafroller in nectarine for your location using the omnivorous leafroller pest model or degree-day table. To learn more about using degree-days to time insecticide applications, watch the degree-days video.

Examine fruit on trees every week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard. Take 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 (PDF) for harvest sample.

• Degree-day calculator
• Degree-day table
• Fruit sampling for pest damage in harvest (PDF)
• Using degree-days to time insecticide applications