How to Manage Pests

UC Pest Management Guidelines

Citrus

Citrus Cutworm

Scientific Names: Egira (Xylomyges) curialis

(Reviewed 9/08, updated 6/13)

In this Guideline:


Description of the Pest

Of the cutworms, generally only citrus cutworm is an economic pest. Other species, most notably the variegated cutworm, Peridroma saucia, are occasionally found on citrus but rarely cause economic damage.

Citrus cutworm has only one generation a year. The grayish citrus cutworm moths emerge from early January to the end of April, with peak emergence during March. After mating, female moths lay their round, milky-white eggs mainly on the upper side of new leaves in clusters of 40 to 225. In a few days eggs turn dark in color as larvae develop inside; they hatch in 5 to 10 days. Young larvae are usually light green in the first three instars and pinkish or brown in the fourth and fifth. All but the youngest larvae have a whitish stripe along each side of the body. The skin appears smooth to the naked eye; it does not have conspicuous hairs or tubercles. When disturbed, older larvae curl up and drop to the ground.

Larvae mature in 3 to 6 weeks; the greatest number of larvae is usually found from mid-March to the first of May, but sometimes even later. Mature larvae drop to the ground and pupate in soil. Pupae remain dormant until the following spring.

Damage

Damage by citrus cutworm can be substantial because they feed on young fruit. In addition, larvae of the citrus cutworm move around while feeding, usually taking a few bites from numerous leaves, blossoms, or fruit. Young larvae feed mostly on the edges of tender leaves; older larvae eat holes through leaves and blossoms and into fruit. A smaller number of citrus cutworms cause more damage than larger numbers of other caterpillars because they are larger and move throughout the tree during feeding. After petal fall, young fruit often have feeding scars; maturing fruit are rarely attacked.

Management

Citrus cutworm is not a pest in all orchards or every year, and populations have declined in the San Joaquin Valley with the shift from organophosphate insecticides to insect growth regulators for scale control and spinosad (Entrust, Success) for citrus thrips control. Natural enemies play a significant role in reducing cutworm numbers and their presence should be preserved by selecting the most specific (those that are only toxic to a narrow range of insects and mites) treatment materials. Treatments may be necessary during bloom and when fruit are young if monitoring indicates a need.

Biological Control

Two parasites attack citrus cutworm larvae and are highly effective in reducing the next year's population. Ophion sp., a parasitic wasp, attacks cutworms just before they are ready to mature. Parasitized larvae pupate in the soil where they are consumed by the parasite larvae.

Another parasitic wasp, Banchus sp., also attacks cutworm larvae. In some groves, a fungal pathogen has been found to infect and kill up to 25% of the pupae.

Organically Acceptable Methods

Biological control and sprays of Bacillus thuringiensis are acceptable for use on organically certified citrus.

Selectivity

The Bacillus thuringiensis (Bt) insecticides, both the aizawai and kurstaki strains, 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 to beneficial insects and mites that feed on other citrus pests. Broad-spectrum organophosphates (chlorpyrifos-Lorsban) and carbamates (methomyl-Lannate) are disruptive to many of the beneficial insects and mites. Some populations of the beneficial mite, Euseius tularensis, show resistance to chlorpyrifos, so this is the least toxic of the broad-spectrum pesticides.

Monitoring and Treatment Decisions

Male moths of citrus cutworm can be monitored using a synthetic female pheromone-treated lure in a bucket trap with a no-pest strip inside to kill the moths. One trap per 10-acre orchard is sufficient. Place the trap in the orchard on January 15 and check the bucket for moths each week. This trap can be used to predict when the larvae will emerge so that larval sampling begins at the right time and selective insecticide treatments can be applied when larvae are young. Using a lower developmental threshold of 46°F and a biofix of the second week of consecutive moth flight in January, begin sampling for larvae at 250 degree-days. You will see larvae emerging at about 350 to 400 degree-days after the biofix.

Monitor larvae using a time search method (number of larvae per hour search) or by shaking the foliage into a sweep net. Before petal fall, the thresholds are 40larvae per hour search and 10 to 15 larvae per 25 net shakes. During or after petal fall, the cutworm can cause more damage and the thresholds drop to 10 to 15 larvae per hour search and 3 to 5 larvae per 25 net shakes.

Monitor orchards weekly from early to mid-April through post petal fall. The most critical period is late bloom until the end of petal fall when cutworm larvae are attracted to the small developing fruit. If populations begin to approach the threshold during this period, monitor twice weekly until the population pupates.

Selective insecticides such as Bacillus thuringiensis or cryolite are slow acting because they are stomach poisons and require warm weather so that the larvae are actively feeding. These pesticides are most effective when applied about 400-500 degree-days after moths begin flying, when the population consists primarily of 1st and 2nd instar larvae.

Common name Amount to use R.E.I.‡ P.H.I.‡
(example trade name) (type of coverage)** (hours) (days)

  Calculate impact of pesticide on air quality

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. AIZAWAI#
  (various products) Label rate (OC) 4 0
  MODE OF ACTION GROUP NUMBER1: 11
  . . . or . . .
  BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rate (OC) 4 0
  MODE OF ACTION GROUP NUMBER1: 11
  RANGE OF ACTIVITY: Pests: narrow (caterpillars); Natural enemies: none
  PERSISTENCE: Pests: short; Natural enemies: none
  COMMENTS: Can be used during bloom. Timing is important because of short residual period. 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: unknown
  COMMENTS: Check label for variety. Use higher rate for larger worms and 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.
 
C. CHLORPYRIFOS*
  (Lorsban Advanced) 2–7 pt/acre (OC or A) 5 days 21
  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. During the bloom period, apply from 1 hour after sunset until 2 hours before sunrise.
 
D. CARBARYL*
  (Sevin XLR Plus) 2 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.
 
E. NALED
  (Dibrom 8 Emulsive) 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 material is hazardous to bees. Do not apply during bloom.
 
F. METHOMYL*
  (Lannate LV2.4) 1.5–3 pt/acre (OC or A) 3 days 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. This material is hazardous to bees. Do not apply during bloom.
 
** A - Aircraft applications 5-20 gal water/acre.
  OC - Outside coverage uses 100–250 gal water/acre.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441

Insects, Mites, and Snails

  • E. E. Grafton-Cardwell, Entomology, UC Riverside and Kearney Agricultural Center, Parlier
  • J. G. Morse, Entomology, UC Riverside
  • N. V. O'Connell, UC Cooperative Extension, Tulare County
  • P. A. Phillips (emeritus), 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 Co., 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
  • 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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