How to Manage Pests

UC Pest Management Guidelines

Citrus

Black Scale

Scientific Name: Saissetia oleae

(Reviewed 9/08, updated 8/15)

In this Guideline:


Description of the Pest

Black scale is one of the soft scales. Female black scales reproduce without mating and lay 1,000 to 2,000 eggs over a period of 2 to 3 months, mainly during May and June and again from October through November in areas with two broods per year (cooler coastal regions). Crawlers move about for some time before settling on leaves. In the late second instar, a ridge develops on the scale's back and later expands into an H shape. After the second molt, young scales migrate to twigs where they grow rapidly and become nearly circular; their covers become dark mottled gray and leathery. Once egg laying starts, the covers become harder and darker and the H-shaped ridge often disappears.

Damage

Black scale is a major citrus pest in Southern California but occurs only occasionally on citrus in the San Joaquin Valley, mostly on grapefruit or on trees near olives. Feeding by black scale reduces tree vigor and can cause leaf or fruit drop and twig dieback. Excreted honeydew supports the growth of sooty mold.

Management

The black scale tends to be a problem in coastal, intermediate, and interior districts of Southern California, where it is a cyclical pest that requires intervention every 5 to 10 years. If parasite activity is disrupted by ants, dust, or pesticides, a treatment or two may be necessary. Be sure to check scale populations for parasite emergence holes before treatment to prevent treating highly parasitized populations (a common error).

Biological Control

Several predators and parasites have been introduced against the black scale. Metaphycus helvolus is a parasitic wasp that provides substantial control of black scale in southern California. In addition to laying its eggs in the scale, the adult female parasite kills and feeds on the body fluids of young scales. This parasite is more effective in coastal areas where overlapping scale generations provide susceptible stages for a longer time than in the interior regions. If available, M. helvolus can be released; this is best done in late summer or early fall. Parasites can also be introduced from other groves with high parasite populations by cutting branches with black scales (before emergence holes are present) and putting them in groves where parasite activity is low. If ants are present, control them.

Organically Acceptable Methods

Biological control and the use of organically approved oils are acceptable methods to use on an organically certified crop.

Monitoring and Treatment Decisions

Watch for newly settled scales in late June or early July; an oil treatment is often sufficient for control. Apply oil as soon as possible after completion of major hatch but before the H formation (rubber stage) becomes apparent on young scale covers in September.

Common name Amount to use REI‡ PHI‡
(Example trade name) (type of coverage)** (hours) (days)

UPDATED: 8/15
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. METAPHYCUS HELVOLUS# 1,000–2,000/acre per year NA NA
  RANGE OF ACTIVITY: Pests: narrow (soft scales); Natural enemies: none
  PERSISTENCE: Pests: long, unless broad-spectrum pesticides used; Natural enemies: none
  COMMENTS: Release a minimum of 1,000 adults/acre per year. Make releases of this parasitic wasp in late summer or early fall; it parasitizes only smaller stages of the scale. Must also control ants for parasites to be effective.
 
B. NARROW RANGE OIL
  (415, 435, 440) 1.2–1.4% (TC) 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.
  COMMENTS: To avoid phytotoxicity problems, see timings for California red scale. Apply higher rate of narrow range oil in July or Aug. only. Narrow range 440 (or higher) spray oil is preferable in the Central Valley during warmer months because of greater persistence, but risk of phytotoxicity increases unless using products with 99% unsulfonated residues (UR). The use of oil also speeds up the weathering and flaking off of honeydew and sooty mold from leaves and fruit. Caution: Serious hazards are associated with oil treatments to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
 
C. CARBARYL*
  (Sevin XLR Plus) 3–5 qt/acre (TC) See label 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. Do not exceed 25 lb/acre per crop. Apply as soon as practical after completion of major hatch.
 
D. CARBARYL*
  (Sevin XLR Plus) 3–5 qt/acre (TC) See label 5
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: long; Natural enemies: long
  MODE-OF-ACTION GROUP NUMBER1: 1A
  . . . PLUS . . .
  NARROW RANGE OIL
  (415) 0.5–1.4% 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.
  COMMENTS: For use on all varieties. Full or half rates of carbaryl or oil may be used. Reducing the rate of carbaryl increases survival of natural enemies. Reducing the rate of the oil reduces the risk of phytotoxicity, especially in warmer growing areas of the state. Do not apply during bloom or exceed 25 lb/acre per crop. May increase citrus red mite populations. Caution: Serious hazards are associated with oil treatments to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
 
E. MALATHION
  (Malathion 8) 1 pt/100 gal (TC);
7.5 pt/acre maximum
72 7
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: For use on all varieties.
 
F. MALATHION
  (Malathion 8) 1 pt/100 gal (TC);
7.5 pt/acre maximum
72 7
  RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most
  PERSISTENCE: Pests: intermediate; Natural enemies: intermediate
  MODE-OF-ACTION GROUP NUMBER1: 1B
  . . . PLUS . . .
  NARROW RANGE OIL
  (415) 0.5–1.4% 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.
  COMMENTS: For use on all varieties. Caution: Serious hazards are associated with oil treatments to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
 
** LV - Low-volume uses 20–100 gal water/acre.
  TC - Thorough coverage uses 750–2,000 gal water or more/acre, depending on tree size.
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). For additional information, see their Web site at http://www.irac-online.org/. ("un" = unknown or uncertain mode of action)
NA Not applicable.

[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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