Description of the Pest
Fruittree leafroller and omnivorous leafroller are the primary leafrollers found in nursery stock, but obliquebanded leafroller and orange tortrix can also be found. There are other leafrollers such as Amorbia or western avocado leafroller, Amorbia cuneana, which attacks avocado primarily, and light brown apple moth (Epiphyas postvittana), which has been detected in California but is not established in the state.
Fruittree leafrollers have one generation per year. Overwintering eggs hatch in spring, and larvae can be found feeding on leaves until about June. The larvae are dark green caterpillars with black heads. Adult moths appear in June or July and lay the overwintering eggs.
The fruittree leafroller overwinters in flat egg masses on scaffold limbs and twigs. Eggs hatch in spring from March to as late as mid-May in cooler areas. Young larvae are dark green caterpillars with black heads. As the larva matures, its head turns dark brown and the plate immediately behind the head becomes a tan to olive-green color. Larvae roll a leaf and web it together to form a protective shelter. At maturity the larvae are 0.75 to 1 inch long. When disturbed, they wiggle backwards and drop to the ground on a silken thread. The pupa is just under 0.5 inch long, light to dark brown, and is usually formed within the rolled leaf.
The adult moth has a wingspan of less than one inch. Like other leafrollers, its wings have a bell-shaped outline when viewed from above. The forewings are mottled shades of brown and tan with gold-colored flecks, while the hind wings are whitish to gray.
Omnivorous leafrollers generally overwinter as adults, emerging in March. Caterpillars may differ in body color from cream to brown with light brown to black head capsules and resemble other tortricid species, except that they have white, slightly convex and oval tubercles at the base of each bristle on the upper side of the abdomen. Mature larvae are about 0.6 inch (1.5 cm) long and are green to cream colored but so translucent that you can see the main blood vessel running down their backs.
Adults are small, dark brown moths, 0.375 to 0.5 inch long with a dark band on the wing and a long snout. Female moths lay overlapping eggs in clusters that resemble fish scales on the upper surface of leaves. Often eggs are laid on weed hosts such as horseweed, common lambsquarters, little mallow, curly dock, and legumes. Omnivorous leafroller has four to six generations per year depending on climatic conditions.
Obliquebanded leafroller may be the most common leafroller found in the Sacramento Valley. It has two generations per year in the Sacramento Valley. Larvae are yellowish green caterpillars with brown to black heads. The obliquebanded leafroller appears about the same time in spring as the fruittree leafroller and resembles the fruittree leafroller as a larva. The obliquebanded leafroller, however, has multiple generations each year and is present throughout the summer.
Adults (moths) of obliquebanded leafrollers are reddish brown and have alternating light and dark brown bands across their forewings. Obliquebanded leafroller overwinters as larvae in the bud scales of twigs. They begin emerging in mid-May in warmer districts to early June in cooler areas. There are two to three generations each year.
Another leafrolling caterpillar, orange tortrix, occurs throughout the year. As a larva, it is about 0.5 inch long when mature and varies in color from light green to tan. The activities of orange tortrix and obliquebanded leafrollers are similar to those of the fruittree leafroller, but unlike the fruittree leafroller, which overwinters in the egg stage, these two species overwinter as larvae.
Light brown apple moth, an exotic pest native to Australia, has been detected in California but has not been established here. Because it is a quarantine pest with special requirements regarding inspection and treatment, consult the University of California's online publication and the California Department of Food and Agriculture (CDFA) website or a County Agricultural Commissioner. The light brown apple moth larvae cannot be reliably identified using morphological characters with our current knowledge. Deliver suspect larvae (see field identification guide ) to CDFA, usually via a county agricultural commissioner, for proper identification. The most efficient and reliable way of obtaining male adults is with the use of light brown apple moth pheromone traps. There are many native tortricids that can be confused with this pest. If you find a tortricid moth in a light brown apple moth pheromone trap, take it to your county agricultural commissioner's office for positive identification.
Leafrollers, which can feed on leaves and flower buds, are generally minor pests in ornamental nursery crops but can be a serious defoliating pest when populations are high. In spring, small larvae spin webs and feed on new foliage. They can attack a wide variety of trees including deciduous and live oaks, ash, birch, California buckeye, box elder, elm, locust, maple, poplar, and willow. Roses can also be targets.
Regular monitoring each season is important so that prompt action can be taken if damaging populations develop. Throughout the year, watch for the presence of leafrollers while monitoring for other pests.
A number of general predators, such as lacewing larvae, assassin bugs, tachinid flies, and wasp parasites attack leafroller larvae or eggs. These natural enemies help keep fruittree leafroller populations at low, nondamaging levels, but occasional outbreaks occur. 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 these and other pests.
Inspect plants during the winter period for egg masses. Egg masses are about the size of a thumbprint and laid on smooth wood. Also check blooms and leaves for the presence of the leafroller and other larvae. To monitor caterpillars, search the outer canopy. Begin checking once a week starting from the spring leaf flush. Closely examine blossoms and vegetative shoots in the nursery in the spring for the presence of caterpillars, webbed or rolled leaves, or feeding damage.
Decisions to treat the larval stage of the leafrollers should be based on the presence of caterpillars observed from periodic visual inspection of the plants.
If damaging populations are observed, a number of environmentally friendly chemicals are effective in controlling this pest, including Bacillus thuringiensis and spinosad (Entrust, Conserve).
Bacillus thuringiensis (Bt) is only effective on fruittree leafroller larvae when they are small (less than 0.5 inch long) and usually requires more than one application. Caterpillars must ingest the pesticide to be killed.
Spinosad is a material that is effective on young larvae and is often preferred over Bt because it has a longer residual and slightly more efficacious against older larvae.
The stomach poison cryolite is specific to foliage-feeding pests. These insecticides are relatively nontoxic to parasites that attack the caterpillars and beneficial insects and mites that feed on other citrus pests.
Carbaryl (Sevin) can be effective against leafroller larvae.
Optimum control and a minimum amount of damage by fruittree leafrollers occur when a spray is applied at the time of larval hatching or shortly afterwards. To determine this time, inspect twigs showing flushes of new foliage and look for feeding injury and the small caterpillars. If egg masses are found, check them regularly for signs of larval exit holes. High-pressure spray is needed to force the material into the leaf rolls and other protected areas where larvae are found.
|Manufacturer||REI1||Mode of action2||Comments|
|Valent||4||11||Most effective against early instar larvae; pheromone trapping recommended for timing applications.|
|insect growth regulator||A.||diflubenzuron
|Chemtura||12||15||Include vegetable oil at the rate of 1 qt/acre. Do not apply after petal fall. Do not exceed 2 applications in any given season. Allow 21 days between applications.|
(ProKil Cryolite 96)
|4||5||Do not apply more than 10 times in a 12-month period. Compatible with most beneficials, but highly toxic to bees and hymenopteran parasites. Direct contact can cause significant mortality to Phytoseiulus persimilis.|
|1||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.|
|2||Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|#||Acceptable for use on organically grown ornamentals.|
|*||Restricted use pesticide. Permit required for purchase or use.|