How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Larvae of the fruittree leafroller are green caterpillars that are somewhat flattened and have shiny black heads. The caterpillars tie or roll leaves or blossoms together with silken threads and feed inside these nests. Older caterpillars construct a new nest frequently, often daily. Mature caterpillars pupate inside nests or in thin cocoons on branches or the trunk. Moths emerge about 8 to 12 days later; after mating, females lay egg masses on twigs in the upper part of trees. Eggs overwinter and start hatching in the middle of March; there is only one generation a year.

DAMAGE

Fruittree leafrollers can occasionally cause damage in spring by feeding on newly set fruit or on ripening Valencias, navels, or grapefruit. Early in spring, young larvae feed mostly on new growth flushes, often resulting in curled leaf terminals. In situations where most of the new flush is consumed (e.g., weak or drought stressed trees with little flush), larvae will tie leaves to fruit and bore inside; this injury provides entry sites for secondary decay organisms, and fruit will drop within 1 to 2 weeks.

MANAGEMENT

Fruittree leafroller is a minor pest. Monitor for fruittree leafroller in spring at the same time as citrus cutworm, but count the two species separately. Natural enemies generally are helpful in reducing this pest, and treatments are rarely necessary.

Biological Control
Natural enemies include general predators that prey on small larvae, and Trichogramma spp. that parasitize the eggs.

Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis are acceptable for use in organically certified crops.

Selectivity
The Bacillus thuringiensis (Bt) insecticides (Dipel, Javelin, Cutlass, and MVPII) are toxic only to caterpillar pests. 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. The broad-spectrum organophosphates (Lorsban) and carbamates (Lannate) kill many of the beneficial insects and mites in citrus groves. Some populations of the beneficial mite, Euseius tularensis, show resistance to chlorpyrifos (Lorsban), so this is the least toxic of the broad-spectrum pesticides.

Monitoring and Treatment Decisions
To monitor fruittree leafroller eggs, establish one or two permanent observation trees per site at five locations per block. Before the middle of March, check twigs and small branches thoroughly in the upper one-third of the tree for gray to brown, flat egg masses.

To monitor caterpillars, search the outer canopy of the south and east side of four trees at each sampling site. Spend about 2 to 5 minutes per tree and count all the live leafroller caterpillars. Carry out this procedure in five locations per block. Record the number of worms per unit time and calculate the average number of larvae per hour search. Caterpillars can also be monitored with an L-shaped 1/4 square meter (20 x 20 inches) PVC pipe counting frame to count the number of infested vs. noninfested terminals. Be sure to open nests and count only nests that contain a live worm. Begin counts once a week when the spring feather-leaf flush appears or the first fruittree leafroller caterpillar is seen. Take one sample from the NE corner of 20 randomly selected trees in a diagonal through the block.

When mature fruit are present and 20% or more of the new flush terminals are infested with a live worm, watch carefully for leaves being attached to mature fruit. The potential for damage to mature fruit is greatest at this point. The 20% threshold corresponds to a time search number of about 400 worms per hour. If worms are close to pupating, increase the threshold, especially if fruit is not present. Most larvae pupate before petal fall and treatments are usually not needed.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O‘Connell, UC Cooperative Extension, Tulare County
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
C. E. Kallsen, UC Cooperative Extension, Kern County
D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgments for contributions to Insect, Mites, and Snails:
J. Barcinas, E. S. I., Corona, CA
R. Dunn, Badger Farming County, Exeter, CA
J. Gorden, Pest Management Associates, Exeter, CA
H. Griffiths, E. S. I., Corona, CA
D. Machlitt, Consulting Entomology Services, Moorpark, CA
C. Musgrove, retired entomologist, Riverside, CA
K. Olsen, S & J Ranch, Pinedale, CA
T. Roberts, E. S. I., Corona, CA
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA
K. Godfrey, USDA Biological Control, Sacramento
D. Headrick, California Polytechnic State University, San Luis Obispo
B. Faber, UC Cooperative Extension, Ventura County
J. Kabashima, UC Cooperative Extension, South Coast Research and Extension Center

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