Leafrollers

Leafrollers (family Tortricidae) are named for the larval behavior of tying leaves together with silk to form a shelter in which they feed and commonly pupate. Leafrollers hatch from eggs as caterpillars, develop through several increasingly larger instars (commonly five larval stages), then become pupae from which adult moths emerge. Fruittree leafroller and omnivorous leafroller are the most common species infesting nurseries. These and other leafroller species pictured here side-by-side occur on various ornamental plants in California. When disturbed tortricid larvae commonly wriggle vigorously and drop suspended from plants on a silken thread; these larvae may climb back up the silk to again feed on the host or drift away to settle on nearby plants.

Except for fruittree leafroller, which lays eggs on bark, the adult females lay eggs on foliage overlapping in clusters that resemble fish scales. Except for those of fruittree leafroller, eggs are indistinguishable to species and may be placed on foliage of crops or alternate host weeds, such as common lambsquarters, curly dock, horseweed, little mallow, and various legumes.

Fruittree leafroller can be common in coastal areas and inland valleys. It has one generation per year; other leafrollers discussed here have several generations per year. Fruittree leafroller overwinters as eggs in flat masses on bark of scaffold limbs, trunks, and twigs, hatching in late winter through (in cooler growing areas) spring.

Larvae (caterpillars) are dark to pale green and present only during late winter through early summer. They have a black or brown head and dark prothoracic (area on top behind the head) shield. Fruittree leafroller larvae grow up to 1 inch long. The pupae are about 1/2 inch long and brownish to orange. They occur attached to foliage, in rolled leaves, or in litter or topsoil.

Adults (moths) appear in summer. They are about 3/4 inch long and have mottled dark and light brown forewings. At rest adults appear bell shaped, a characteristic of tortricid adults.

Omnivorous leafroller is a pest mostly in inland valleys. Adults are up to 1/2 inch long and a mix of blackish, brown, gray, and tan. They can be active from late winter through fall. Omnivorous leafroller has four to six generations per year depending on climatic conditions.

The caterpillars grow up to 3/5 inch long and have a black or brown head and prothoracic shield. They vary in coloration, commonly brownish, cream colored, greenish, or yellowish. Mounds (tubercles) at the base of the bristles along top and sides are chalky white. The main blood vessel along the back is often visible through the cuticle as a faint dark stripe.

Obliquebanded leafroller is a pest mostly in inland valleys; it may be the most common leafroller found in the Central Valley of California where it has two to three generations per year. Adult forewing coloration varies from mostly reddish brown to a mix of blackish and orange; generally they have light and darker coloration in broad bands that alternate across the forewings.

Obliquebanded leafroller overwinters as larvae in the bud scales of twigs. They become active and begin feeding during May in warmer locations or early June in cooler areas. Larvae grow up to 1-1/4 inches and are yellowish green caterpillars with brown or black heads. Larvae of obliquebanded leafroller appear about the same time in spring as those of fruittree leafroller and they resemble each other. However, the obliquebanded leafroller continues to be a problem throughout the growing season because it has multiple generations.

Orange tortrix occurs mostly in coastal areas and can be active throughout the year. It overwinters as larvae, which in winter may feed during warmer days. Adults at rest are bell shaped and vary from mostly gray to mostly orangish. Larvae grow to about 1/2 inch long and vary in color from greenish to bright yellow or straw-colored or brown. The head and prothoracic shield are brown, gold, or straw-colored. A row of bristles projecting from the rear of the last abdominal segment (an anal comb) help to distinguish this species from many other caterpillar species.

Light brown apple moth is an introduced species that occurs in at least coastal areas where it feeds on various woody ornamentals. Adult coloration varies from dark to light brown or tan or a mix of these colors. Adult body length ranges from 1/4 to 1/2 inch long.

The caterpillars are a medium to pale green and up to 3/4 inch long. The head and prothoracic shield are black to brown or light green or yellowish. Consult the University of California's Field Identification Guide for Light Brown Apple Moth in California Nurseries (PDF) and the California Department of Food and Agriculture's Light Brown Apple Moth Pest Profile for more information on this species.

Amorbia, also called western avocado leafroller, amorbia occurs in coastal and inland locations. The adult forewings are mostly brown and tan with black markings. Larvae are dark green to yellowish green and up to 1 inch long. They are distinguished from other common leafrollers by the presence of short, black stripes on each side, above the head and above the first pair of legs.

Leafrollers chew leaves and flower buds and web foliage together with silk. They generally are minor pests in nursery crops, but can be serious defoliating pests when broad-spectrum, persistent insecticides applied for other pests prevent their natural enemies from suppressing their populations. Most any broadleaved plant can be infested with one or more leafroller species. Hosts include ash, birch, boxelder, California buckeye, deciduous and live oaks, elm, locust, maple, poplar, rose, and willow.

Conserve natural enemies, exclude egg-laying adult moths, and keep growing areas clean and weed free. Monitor host crops regularly and apply selective insecticides when direct control of caterpillars is warranted.

Conserve natural enemies, which generally keep leafroller populations low in field-grown crops when the application of persistence, broad-spectrum insecticides is avoided for all pests. Parasitic wasps and tachinid flies are especially common in leafroller larvae and pupae. Trichogramma spp. parasites commonly kill the eggs. Assassin bugs, green lacewing larvae, predaceous ground beetles, and certain other beetles are common predators of moth eggs and caterpillars.

To conserve natural enemies, avoid the use of carbamates, organophosphates, pyrethroids, and other persistent, broad-spectrum insecticides for all pests. Where feasible rely on products that conserve (preserve) natural enemies, especially Bacillus thuringiensis. See Biological Control, Protecting Natural Enemies and Pollinators, and Relative Toxicities of Pesticides Used in Floriculture and Nurseries to Natural Enemies and Honey Bees for more information.

Control weeds around growing areas because each leafroller species feeds on numerous alternative hosts. Leafroller adults commonly migrate into crops from nearby unmanaged vegetation, such as during spring when winter annual weeds dry and die. Promptly remove crop debris and weeds and dispose of them in covered containers. Screen greenhouses, shade houses, and seedling flats to exclude the egg-laying adults; use a sufficient surface area of screening to provide adequate ventilation. Floating row covers exclude leafrollers during field production if the mesh is held above plants (e.g., with hoops) to prevent egg laying though the fabric onto plants. To reduce moth attraction to growing areas at night, switch from always-on night lighting to motion-activated security lights.

Biological and cultural controls are organically acceptable management methods. Entomopathogenic nematodes (e.g., Heterorhabditis and Steinernema spp.), and the microbial insecticides Bacillus thuringiensis ssp. aizawai, Bt ssp. kurstaki, and certain spinosad formulations (Entrust Naturalyte, Entrust SC) are acceptable for organic production.

Inspect host plants at least weekly for moth eggs and caterpillars and chewed, rolled, or webbed foliage. If one or a few species of leafroller have historically been problems, deploy several sticky traps baited with the pheromone of those species. Well-maintained traps alert you early to the presence of adults and help in timing insecticide application. Since there commonly is not a direct relationship between the abundance of moths in traps and the number of larvae infesting plants, base any decision to apply insecticide on the presence of caterpillars and moth eggs on crop plants or the history of leafroller problems. See Establishing Action Thresholds for more information.

Optimize control for minimum damage by treating at larval hatch or shortly after. For fruittree leafroller that overwinters as eggs on bark, flag the location of several egg masses and inspect them regularly during late winter and early spring. Apply a selective or semi-selective insecticide when emergence holes are observed in eggs and inspection of nearby plant parts reveals caterpillars are present.

Bacillus thuringiensis (Bt) selectively controls caterpillars that eat treated foliage. Unlike some insecticides it does not disrupt biological control or induce outbreaks of other pests such as spider mites. Insect growth regulators (IGRs) and spinosad are semi-selective controls for caterpillars and certain other types of pests.

Spray foliage at high pressure to help move insecticide into rolled or webbed foliage that partly protects caterpillars. Begin application while most caterpillars are young (early instars) when coverage is best and caterpillars are least protected by webbing and rolled leaves. To improve scouts' ability to detect these pests and improve spray coverage, avoid overcrowding plants.

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