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How to Manage Pests
UC Pest Management Guidelines
Olive
Black Scale
Scientific Name: Saissetia oleae
(Reviewed 1/08,
updated 1/08)
In this Guideline:
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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 leaves and twigs of tree. 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.
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.
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.
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.
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. First,
select 10 trees in each area. 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. 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
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 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
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 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.+ |
| (trade name) |
|
(hours) |
(days) |
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| When choosing a pesticide, consider
information relating to the impact on natural enemies and
honey bees and
environmental impact.
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| SUMMER (July 15–Harvest) |
| A. |
NARROW RANGE OIL# |
Label rates |
4 |
0 |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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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. |
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| B. |
NARROW RANGE OIL |
1.5 gal |
4 |
0 |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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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. |
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. . . PLUS . . . (optional) |
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CARBARYL* |
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(Sevin) 80S |
1–1.25 lb |
12 |
14 |
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MODE OF ACTION GROUP NUMBER1: 1A |
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COMMENTS: Do not exceed 2
applications/year. This material is very destructive to most natural enemies.
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. |
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| POSTHARVEST (Postharvest until scale
develops into rubber stage)
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| A. |
NARROW RANGE OIL# |
Label rates |
4 |
0 |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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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. |
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| B. |
NARROW RANGE OIL |
1.5 gal |
4 |
0 |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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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. |
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. . . PLUS . . . |
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METHIDATHION* |
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(Supracide) 25WP |
2 lb |
48 |
0 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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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/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. |
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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 Co.
R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to the insects and mites section:
G. S. Sibbett, UC Cooperative Extension, Tulare Co.
L. Ferguson, Pomology, UC Davis
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