How to Manage Pests
UC Pest Management Guidelines
Scientific name: Platynota stultana
(Reviewed 5/06, updated 4/09)
DESCRIPTION OF THE PEST
Omnivorous leafroller is a pest of plums primarily in the San Joaquin Valley. It occurs in the Sacramento Valley but seldom causes damage. Omnivorous leafrollers overwinter as immature larvae in mummy fruit and do 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 in March. They are small, dark brown moths, 0.375 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 that hatch from this generation of eggs can cause significant damage in stone fruits. All 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.
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.
Omnivorous leafrollers do not usually appear in plum 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.
A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack omnivorous leafroller larvae. General predators such as green 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 materials that are least disruptive of biological control when treating other pests.
Remove fruit mummies and destroy both the fruit and potential overwintering weed hosts, such as horseweed, common lambsquarters, little mallow, curly dock, legumes, by clean cultivation.
Organically Acceptable Methods
Biological and cultural control along with applications of Bacillus thuringiensis are organically acceptable tools.
Calculate degree-days for omnivorous leafroller in your location.
Learn to use degree-days to time insecticide applications.
Monitoring and Treatment Decisions
Begin monitoring by placing pheromone monitoring traps (see PHEROMONE TRAPS) in the orchard during bloom (by February 20) in the San Joaquin Valley and check twice weekly to establish the biofix for the first flight; biofix is the first night moths are consistently caught in traps. First generation omnivorous leafrollers are most likely on weeds or cover crops; treatments for this first brood are probably not necessary and are likely 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.
It takes about 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 degree-days after the start of the flight. Monitor the fruit closely for signs of damage. No treatment threshold values are available.
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 on a monitoring form .
UC IPM Pest Management Guidelines:
Insects and Mites
Acknowledgment for contributions to Insects and Mites:
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