How to Manage Pests

UC Pest Management Guidelines

Citrus

Amorbia (Western Avocado Leafroller)

Scientific Name: Amorbia cuneana

(Reviewed 2/17, updated 2/17)

In this Guideline:


Description of the Pest (View caterpillar ID key) (PDF)

Amorbia is primarily a pest of avocado, but can also occasionally cause damage in citrus groves, primarily in Coastal and Southern California and the San Joaquin Valley. Adults are bell-shaped when their wings are folded at rest. Amorbia larvae develop through five instars. At maturity they are 0.75 to 1 inch long. Caterpillars are yellowish green when young, and mostly darker green when mature. The larva has two dark horizontal lines on each side of its head and prothoracic shield that distinguish it from other caterpillars that occur in citrus. The female lays about 150 to 200 eggs during her 2 to 3 week life.

Amorbia completes two generations per year in Northern California, where adults are present in May through June and again in October. In Southern California, adults have been recorded every month of the year.

Damage

Amorbia larvae may feed on young fruit at petal fall. They also feed on new growth flushes, often rolling the leaves or tying leaves to fruit and feeding on the peel of young or maturing fruit and under the calyx. Healthy trees tolerate some loss of chewed foliage and blossoms, however extensive defoliation can also result in sunburned fruit and twigs. Economic damage occurs primarily when caterpillars damage fruit. Damaged fruit often decays at the feeding site and scarring causes downgrading or culling of fruit. Infestations generally occur in groves planted near avocado.

Management

Monitor for amorbia from petal fall through fall. Use selective (toxic to only a narrow group of insects) insecticides to preserve natural enemies. Caterpillar outbreaks commonly occur after spraying malathion, which poisons parasites and predators. When pesticides are warranted, limit application to the most infested spots to provide refuges where natural enemies can recolonize after treatment.

Biological Control

A variety of natural enemies such as birds, spiders, lacewings and predaceous bugs attack egg, larval, and pupal stages of amorbia. A naturally occurring virus often kills many amorbia when caterpillar numbers become high. One of the most effective egg parasites is the tiny wasp, Trichogramma platneri. Parasitized eggs are black. Mass releases of T. platneri are used for control in avocado. A tachinid fly and several parasitic wasps attack the larvae. The tachinid fly attaches its eggs near the head of the larva and the emerging maggots bore into the amorbia larva to develop inside. Make at least two releases a week apart during the period of peak egg laying (as determined by pheromone traps and visual inspection). Place parasite egg cards on at least four trees/acre for a total minimum release of 100,000 parasites/acre per season.

Organically Acceptable Methods

Use biological control, sprays of Bacillus thuringiensis, and the Entrust formulation of spinosad in organically managed citrus orchards.

Cultural Control

  • Prune to reduce foliage touching among adjacent trees and to minimize dead twig and plant debris accumulation in canopies.
  • Thin or selectively harvest fruit in clusters. Pruning and thinning reduce protected sites and canopy bridges that facilitate insect movement between trees, thereby reducing the abundance of caterpillars, greenhouse thrips, and mealybugs.
  • Remove abandoned citrus to reduce the likelihood that amorbia will move from citrus to nearby avocado, or vice versa.
  • Control weeds that can host these caterpillars.
  • Reduce dust in groves by driving slowly and oiling or watering dirt roads. Dusty conditions reduce the effectiveness of parasites and predators that attack caterpillars and other pests including mites and scales.
Monitoring and Treatment Decisions

When checking the tree, inspect under the button on the base of fruit for small amorbia larvae when monitoring for citrus thrips at petal fall, especially in groves near avocados. Monitor larger larvae later in spring and summer especially after peaks in moth flights. During spring and summer, consider monitoring where bright lights, such as security lights, are used outdoors because the nocturnal moths are attracted by lights to lay eggs nearby. Search for webbing and leaf rolls in young foliage and feeding damage on young and mature fruit located on the outside canopy. Be sure to correctly distinguish the cause of any damage, as other insects and certain abiotic disorders cause leaf holes resembling caterpillar chewing.

  • Correctly identify the species of caterpillars. Alternate host plants, damage potential, monitoring methods, and natural enemies vary depending on the species of caterpillar.
  • Look for caterpillar predators and larval diseases and parasitism. Natural enemy prevalence affects treatment decision-making because there are no established amorbia thresholds for pesticide application.
  • Monitor parasites and other natural enemies several times to determine if their numbers are increasing. If they are, the amorbia numbers will decrease.

Avoid malathion sprays, which often lead to outbreaks of other pests. Bacillus thuringiensis sprays are the least disruptive to natural enemies and pollinators.

Common name Amount to use REI‡ PHI‡
(Example trade name) (type of coverage)** (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
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. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various) Label rates (OC) 4 0
  RANGE OF ACTIVITY: Pests: narrow (caterpillars); Natural enemies: none
  PERSISTENCE: Pests: short; Natural enemies: none
  MODE-OF-ACTION GROUP NUMBER1: 11A
  COMMENTS: Can be used during bloom. Timing is important because of short residual period and is most effective when used to control early instars of the caterpillar. Apply only during warm weather to control young, actively feeding worms. Use reduced wind velocity and drive 3 mph.
 
B. CRYOLITE
  (Prokil Cryolite 96) 8–20 lb/acre (OC) 12 15
  (Kryocide) 8–20 lb/acre (OC) 12 15
  RANGE OF ACTIVITY: Pests: intermediate (foliage feeders such as worms, katydids, and Fuller rose beetle); Natural enemies: few, if any.
  PERSISTENCE: Pests: long, unless washed off by rain; Natural enemies: none to short
  MODE-OF-ACTION GROUP NUMBER1: 8C
  COMMENTS: Check label for variety. Use higher rate for larger trees. Slow-acting stomach poison that may take several days of warm weather to kill worms. Use reduced wind velocity and a speed of 3 mph. Use of Prokil Cryolite 96 allowed under a supplemental label.
 
C. SPINOSAD
  (Entrust)# 1.25–3 oz/acre (OC) 4 1
  (Success) 4–10 fl oz/acre (OC) 4 1
  RANGE OF ACTIVITY: Pests: narrow (thrips, orangeworms, katydids); Natural enemies: predatory thrips
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
  . . . PLUS . . .
  NARROW RANGE OIL
  (415) 0.25–1% See label See label
  RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: short
  MODE OF ACTION: Contact including smothering and barrier effects; also improves translaminar movement and insecticide persistence.
 
D. CHLORPYRIFOS*
  (Lorsban Advanced) 2–7 pt/acre (OC or A) 5 days See comments
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: short (low rates), intermediate (high rates); Natural enemies: short (low rates), intermediate (high rates)
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: For use on all varieties. Do not apply more than twice per fruit year or make applications less than 30 days apart. During the bloom period, apply from 1 hour after sunset until 2 hours before sunrise. PHI is 21 days for up to 7 pt/acre or 35 days for over 7 pt/acre. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. Certain formulations emit high amounts of volatile organic compounds (VOCs); use low-VOC formulations. Regulations affect use for the San Joaquin Valley from May 1 to October 31, 2017. Review the Department of Pesticide Regulation's updated fact sheet.
 
E. CARBARYL*
  (Sevin XLR Plus) 2–3 qt/acre (OC) 12 5
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: long; Natural enemies: long
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: For use on all varieties. During the bloom period, apply from 1 hour after sunset until 2 hours before sunrise. Check with your local county agricultural commissioner regarding application restrictions during the bloom period. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
F. NALED
  (Dibrom 8 Emulsive)* 1–2 pt/acre (OC) 48 7
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: intermediate
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: For use on grapefruit, lemons, oranges, tangerines. This pesticide is hazardous to bees. Do not apply during bloom. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
G. METHOMYL*
  (Lannate LV) 1.5–3 pt/acre (OC or A) 72 1
  (Lannate SP) 0.5–1 lb/acre (OC or A) 72 1
  RANGE OF ACTIVITY: Pests: broad (many insects) Natural enemies: most
  PERSISTENCE: Pests: short; Natural enemies: intermediate
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: For use on grapefruit, lemons, oranges, tangerines, and tangelos. Apply as needed, except during daylight hours of the bloom period. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
** A - Aircraft applications 5 to 20 gal water/acre.
  OC - Outside coverage uses 100 to 250 gal water/acre.
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 two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.
1 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

Insects, Mites, and Snails

E. E. Grafton-Cardwell, Lindcove Research and Extension Center, Exeter and Entomology, UC Riverside
J. G. Morse, Entomology, UC Riverside
D. R. Haviland, UC Cooperative Extension, Kern County and UC IPM Program
B. A. Faber, UC Cooperative Extension, Santa Barbara and Ventura counties

Acknowledgments for contributions to Insect, Mite, and Snails:
J. Barcinas, E.S.I., Corona, CA
R. Dunn, Badger Farming Co., Exeter, CA
J. Gorden, Pest Management Associates, Exeter, CA
C. E. Kallsen, UC Cooperative Extension, Kern County
D. Machlitt, Consulting Entomology Services, Moorpark, CA
C. Musgrove, retired entomologist, Riverside, CA
K. Olsen, S & J Ranch, Pinedale, CA
N. V. O'Connell, UC Cooperative Extension, Tulare County
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
T. Roberts, E.S.I., Corona, CA T. Shea, UC Cooperative Extension, Riverside County J. Stewart, Pest Management Associates, Exeter, CA P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

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