Description of the Pest
Fruittree leafrollers overwinter in the egg stage on limbs. Eggs hatch in early spring. Larvae are dark green with black heads and are about 1 inch long when fully grown; they are difficult to distinguish from obliquebanded leafroller. Adult moths emerge in June or July and deposit overwintering eggs. Adults appear bell-shaped when at rest and have dark brown bands running at oblique angles across their wings. The wings are mottled with gold and white flecks. There is one generation a year.
Obliquebanded leafrollers occur on a wide range of plants. These leafrollers overwinter as either a second- or third-stage larva within a silken case or hibernaculum. These hibernacula can be found in protected areas of the scaffold limbs, such as pruning scars. The overwintered larvae become active as the buds begin to open. They begin to feed by tying together a number of leaves with silk. They first feed on water sprouts and then move throughout the tree. Those feeding on developing flower buds do so before bloom and continue to consume floral parts throughout the blossom period. This is when they cause the most damage to the almond crop. After petal fall, these larvae continue to feed on developing fruit. Pupation occurs within these sheltered areas and the adult moths generally appear during late May and early June. Eggs are laid in flattened, overlapping masses of up to 300 on the upper surface of leaves. Emerging larvae are greenish yellow caterpillars, usually with black heads but sometimes with lighter-colored heads. Adults are reddish brown moths with alternating light and dark brown bands on the wings; the bands are oblique or chevron-shaped. There are two or three generations a year in the Central Valley.
Leafrollers are occasional pests of almonds. The primary damage occurs early in the season when larvae of the overwintered generation feed on developing nuts and hollow them out. Many of the damaged nuts are lost in the June drop, presumably reducing yield. The summer generation of the obliquebanded leafroller ties leaves and nuts together and feeds on the hulls. Leafroller feeding on the hulls increases later nut infestation by navel orangeworm.
Treatment is not normally needed unless leafrollers numbers are high. If treatment is required, Bacillus thuringiensis, spinosad (Entrust, Success) and methoxyfenozide (Intrepid) are environmentally sound insecticides that control leafrollers with less harm to natural enemies.
The parasitic wasp, Macrocentrus iridescens, attacks obliquebanded leafroller larvae in the Central Valley, often with multiple cocoons on one host caterpillar.
Organically Acceptable Methods
Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable insecticides.
Monitoring and Treatment Decisions
Calculate degree-days for obliquebanded leafroller in your location.
Learn to use degree-days to time insecticide applications.
In orchards with a history of obliquebanded leafroller problems, monitor after bloom by putting out pheromone traps and sampling developing fruit.
- Put out pheromone traps by mid-April. (The lower-load-rate pheromone lures are the best indicators of leafroller numbers.)
- Begin accumulating degree-days once moths have been caught in pheromone traps on two or more consecutive observation dates (the biofix). Use a lower threshold of 43°F and an upper threshold of 85°F (vertical cutoff).
- Begin sampling for larval feeding or for leaves that are tied together at 930 degree-days from the biofix.
- Apply a treatment when larval activity is first detected; larvae are difficult to control once they are sheltered in leaves that are webbed together.
If bloom time sprays for peach twig borer are applied, both leafroller species will be controlled.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|Note: Additional insecticides are labeled for use during bloom. However, due to concerns over pollinator safety (adult, developing brood in the hive, or both), applications of other insecticides by themselves or in combination with fungicides should be delayed until bloom is complete and hives are removed.|
|A.||BACILLUS THURINGIENSIS ssp. KURSTAKI#|
|(various products)||Label rates||4||0|
|MODE-OF-ACTION GROUP NUMBER1: 11A|
|COMMENTS: Effective only under moderate pest pressure. Make 2 applications during bloom: the first between popcorn and the beginning of bloom and the second 7 to 10 days later, but no later than petal fall. Compatible with fungicide sprays and can be tank mixed with them. Good coverage is essential. Ground application using a concentrate rate (80–100 gal water maximum) is preferred. If aerial applications must be made because conditions do not permit ground application, a concentrate rate (5 gal or less) is preferred. Apply aerially at a height of about 20 feet over the canopy using appropriate nozzles to allow better deposition on the treetops.|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: A fermentation-derived insect control product. May be disruptive of natural enemies except predaceous thrips and some parasitoids.|
|(Delegate WG)||3–7 oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: Apply at night to target active adult moths and to avoid foraging bees when blooming groundcover is present. May be disruptive of natural enemies except predaceous thrips and some parasitoids.|
|(Intrepid 2F)||24 fl oz||4||14|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|(Proclaim)*||3.2–4.8 oz||See label||14|
|MODE-OF-ACTION GROUP NUMBER1: 6|
|‡||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. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI The longer of these two intervals is the minimum time that must elapse before harvest may occur.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|#||Acceptable for use on organically grown produce.|
|1||Rotate pesticides 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; pesticides with a 1B group number should be alternated with pesticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|