How to Manage Pests

UC Pest Management Guidelines

Olive

Black Scale

Scientific Name: Saissetia oleae

(Reviewed 3/14, updated 3/14)

In this Guideline:


Description of the pest

Black scale adult females are about 0.2 inch (5 mm) in diameter and dark brown or black with a prominent H-shaped ridge on the back. Young scales are yellow to orange crawlers and are found on the leaves and twigs of trees. A hand lens is usually needed to detect the crawlers. Black scales are in the soft scale family (Coccidae) and usually have one generation per year in interior valley olive-growing districts. In cooler, coastal regions multiple generations occur. Black scale prefers dense, unpruned portions of trees. Open, airy trees rarely support populations of black scale.

Damage

Young black scales excrete sticky, shiny honeydew on leaves of infested trees. At first, affected trees and leaves glisten and then become sooty and black in appearance as sooty mold fungus grows on the honeydew. Infestations reduce vigor and productivity of the tree. Continued feeding reduces bloom the following year. Olive pickers are reluctant to pick olive fruits covered with honeydew and sooty mold. Cultivars with dense canopies are more likely to be affected.

Management

Biological control and pruning to open up closed canopies are key to managing black scale. Monitor to detect the presence of honeydew on leaves and track black scale population levels in olive groves. Control ants in the orchard because they disrupt biological control (for more information, see ANTS).

Biological Control

A number of parasites attack black scale, the most common are Metaphycus helvolus, M. bartletti, and Scutellista caerulea (=S. cyanea). These parasites, combined with proper pruning, provide sufficient control in northern and coastal orchards. In other regions, biological control is often ineffective because black scale's development pattern hampers parasite establishment. In addition, where insecticides such as carbamates (IRAC Group 1A), organophosphates (1B), and pyrethroids (3) are used, biological control will be disrupted. Be sure to monitor scale populations if disruptive insecticides are used.

Cultural Control

Pruning to provide open, airy trees discourages black scale infestation and is preferred to chemical treatment.

Organically Acceptable Methods

Biological and cultural control and certain oil sprays are acceptable to use in an organically certified crop.

Monitoring and Treatment Decisions

The first indication of black scale is usually the presence of honeydew on the leaves. Check 25 to 30 trees during April and October, the two periods of greatest honeydew accumulation, to get an idea of population levels.

Sample for adult scales in May, focusing on two to three areas in each block, particularly those that have had scale problems in the past.

  1. First, select 10 trees in each area.
  2. Count the number of adults on the terminal 18 inches of 10 branches on each tree; be sure to include the lower, inner, and outer sections of the tree.
  3. Sum the numbers of black scale in each 10-branch sample and divide by the number of branches sampled to determine the infestation level.

Infestations fall into one of four levels: light (0 to fewer than an average of 1 per branch sampled), moderate (1 to 4), heavy (4 to 10), and severe (more than 10).

Light infestations

These typically do not require treatment in open-canopy orchards. Closed-canopy orchards should be pruned and an application of a dormant oil considered.

Moderate infestations

These may occur following a cool summer or within a closed orchard canopy. This level of scale infestation typically does not cause damage; however, it presents the potential for substantial damage and economic losses the next year. In trees with open canopies, the scale population should decrease or remain stable, depending on summer temperatures. If the summer is mild, apply a narrow range oil. If trees in the orchards have closed canopies, prune them and apply oil or an oil + insecticide combination treatment.

Heavy infestations

These can cause economic damage; if left untreated, the next generation will inflict substantial crop loss. Heavy infestations are rare in open canopies, but orchards with closed canopies must be pruned, chemically treated, or both.

Severe infestations

These occur in closed-canopy orchards in which treatment of moderate or heavy scale infestations is delayed. Economic loss can be extensive. Prune the orchard, removing severely damaged branches, and treat with an insecticide. The best application timing is after egg hatch to treat the crawlers (mid-July) but before August to avoid damage to the following year's crop.

Common name Amount to use** R.E.I.‡ P.H.I.‡
(example trade name)   (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.
 
SUMMER (JULY 15–HARVEST)
 
A. NARROW RANGE OIL#
  (Organic JMS Stylet Oil, etc.) Label rates 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Effective against light to moderate infestations, especially when used in conjunction with pruning to open the orchard canopy. Do not apply any oil between August 20 and harvest to olives used for Spanish or green-ripe processing due to fruit spotting. Most effective when applied against the crawler stage. Spray at night or early morning if temperatures are expected to exceed 90°F during the day. Check with certifier to determine which products are organically acceptable.
 
B. NARROW RANGE OIL 1.5 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: For heavy to severe infestations, add the following insecticide to the oil spray. Do not apply any oil between August 20 and harvest to olives used for Spanish or green-ripe processing due to fruit spotting. Spray at night or early morning if temperatures are expected to exceed 90°F during the day.
  . . . plus . . . (optional)
  CARBARYL*
  (Sevin SL) 5.0–7.5 qt 12 14
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not exceed 2 applications per year. This material is very destructive to most natural enemies. To protect honeybees, apply only during late evening, night, or early morning when bees are not present. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i.
 
POSTHARVEST (POSTHARVEST UNTIL SCALE DEVELOPS INTO RUBBER STAGE)
 
A. NARROW RANGE OIL#
  (Organic JMS Stylet Oil, etc.) Label rates 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Effective against light to moderate infestations, especially when used in conjunction with pruning to open the orchard canopy. Most effective when applied against the crawler stage. Spray at night or early morning if temperatures are expected to exceed 90°F during the day. Check with certifier to determine which products are organically acceptable.
 
B. PYRIPROXYFEN
  (Esteem 0.86EC) 13–16 fl oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 7C
  COMMENTS: Insect growth regulator. Has no activity on adult stage but hatching of eggs laid by treated adults will be suppressed. Most effective when applied against the crawler stage. Use higher rate for high scale numbers.
 
C. NARROW RANGE OIL 1.5 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: For heavy to severe infestations, add the following insecticide to the oil spray. Spray at night or early morning if temperatures are expected to exceed 90°F during the day.
  . . . plus . . .
  METHIDATHION*
  (Supracide 25WP) 2 lb 48 0
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Use with or without oil. Application of methidathion with, or closely following, a fungicide containing lime will negate the insecticide's effectiveness. The application of this material should precede the application of fungicides containing lime. Do not apply more than 12 lb/acre per year. For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i. To protect honeybees, apply only during late evening, night, or early morning when bees are not present.
 
** Amounts per 100 gal water (except where otherwise stated), using 400-500 gal solution per 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 R.E.I. exceeds the P.H.I. 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 crops.
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 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: Olive
UC ANR Publication 3452

Insects and Mites

F. G. Zalom, Entomology, UC Davis
P. M. Vossen, UC Cooperative Extension, Sonoma County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
M. W. Johnson, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
G. S. Sibbett, UC Cooperative Extension, Tulare County
L. Ferguson, Pomology, UC Davis

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