How to Manage Pests

UC Pest Management Guidelines

Citrus

Black Scale

Scientific Name: Saissetia oleae

(Reviewed 2/17, updated 2/17)

In this Guideline:


Description of the Pest

Black scale is one of the soft scales, which produce a soft, thin, cottony, powdery or waxy layer over themselves that cannot be separated from the insect body. These scale insects often produce copious amounts of honeydew.

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 around 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

Scale insects feed by sucking sap from trees and shrubs through piercing-sucking mouthparts. Sap feeding by scale insects may cause fruit drop, wilting of leaves, stunting or unthrifty appearance of the plants, twig dieback and eventually death of all or part of the plant when infestations are heavy. Weakened plants may lose vigor and become more susceptible to injury caused by drought, severe winters, attack by other insects, or infection by diseases. 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.

While feeding, black scale excretes a sweet, sticky honeydew. Honeydew is a mixture of undigested sugar and water passed through the insect's digestive system and deposited onto leaves and stems. Honeydew may make the plant appear shiny and wet and also attracts flies, ants, bees, and other insect scavengers. The honeydew may encourage a fungus called sooty mold that gives the plants a characteristic black, "sooty" appearance.

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 pesticide application or two may be necessary. Be sure to check scales for parasite emergence holes before a pesticide application to prevent spraying 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 numbers 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

Use biological control and organically approved oils on an organically certified crop.

Monitoring and Treatment Decisions

Watch for newly settled scales in late June or early July; an oil application is often sufficient for control. Apply oil or pyriproxyfen 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)
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. 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 August 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 sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
 
C. PYRIPROXYFEN
  (Esteem 0.86 EC) 16 fl oz/acre (TC or LV) 12 1
  RANGE OF ACTIVITY: Pests: narrow (armored scale insects); Natural enemies: predatory beetles
  PERSISTENCE: Pests: long; Natural enemies: long
  MODE-OF-ACTION GROUP NUMBER1: 7C
  ...PLUS...
  415 NARROW RANGE OIL 0.5–1% 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; also improves insecticide spread and persistence.
  COMMENTS: For use on all varieties. Toxic to vedalia beetles needed for cottony cushion scale control. Apply after the crawlers have settled down. This product does not kill the scale until they molt, so a decrease in scale numbers is usually not observed until the next generation.
 
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
  COMMENTS: For use on all varieties. Do not exceed 25 lb/acre per crop. Apply as soon as practical after completion of major hatch.
 
E. 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 numbers. Caution: Serious hazards are associated with oil sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
 
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
  COMMENTS: For use on all varieties.
 
G. 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 effects.
  COMMENTS: For use on all varieties. Caution: Serious hazards are associated with oil sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
 
** TC - Thorough coverage uses 750 to 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).
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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