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How to Manage Pests
UC Pest Management Guidelines
Citrus
Black Scale
Scientific Name: Saissetia oleae
(Reviewed 7/03,
updated 7/05)
In this Guideline:
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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 (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. 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 intermediate and interior
districts, where it is a cyclical pest that requires intervention every 5-10
years. If parasite activity is disrupted by ants or pesticides, a treatment or
two may be necessary.
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 feeds on the body fluids of young scale. 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. If ants are present, control
them.
Organically Acceptable Methods
Biological control and petroleum oil sprays are acceptable methods for
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 |
Minimum Days before
Harvest+
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| (trade name) |
(type of coverage)** |
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| A. |
METAPHYCUS HELVOLUS# |
1,000–2,000/acre/year
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RANGE OF ACTIVITY:
Narrow (soft scales)
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PERSISTENCE:
Long (unless broad-spectrum pesticides are used)
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COMMENTS: Release a minimum of 2,000 adults/acre/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.
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| B. |
NARROW RANGE OIL# |
1.2–1.4 gal/100 gal
(TC)
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4 hours
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(415, 440) |
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RANGE OF ACTIVITY:
Broad (unprotected stages of insects and mites)
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PERSISTENCE:
Short
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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 spray oil is preferable in the Central Valley during
warmer months because of greater persistence, but risk of phytotoxicity
increases. 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.
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| C. |
CARBARYL* |
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(Sevin) 80S |
1–1.2 lb/100 gal (TC)
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5
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RANGE OF ACTIVITY:
Broad (insects and beneficial mites)
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PERSISTENCE:
Long
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COMMENTS: For use on all varieties. Do not exceed 25
lb/acre/application. Apply as soon as practical after completion of major
hatch.
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| D. |
CARBARYL* |
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(Sevin) 80S |
0.4 lb/100 gal (TC)
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5
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...PLUS... |
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NARROW RANGE OIL |
0.5–1.4 gal/100 gal
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(415, 440) |
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RANGE OF ACTIVITY:
Broad (insects and beneficial mites)
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PERSISTENCE:
Long
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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/application. 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.
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| E. |
METHIDATHION* |
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(Supracide) 25WP |
0.5–1 lb/100 gal (TC)
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14
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...or...
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12–16 lb/acre (LV)
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60
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RANGE OF ACTIVITY: Broad (insects and beneficial
mites)
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PERSISTENCE: Long |
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COMMENTS: For use on all varieties. Do not apply during bloom
or exceed 40 lb/acre/season or 2 applications/fruit year, 45 days apart for
dilute (TC) sprays. Only 1 application allowed for low-volume (LV) treatments.
Low-volume application is available under a Special Local Needs permit.
Preferred timing is immediately postbloom before fruit becomes infested. May
increase citrus red mite populations.
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| F. |
METHIDATHION* |
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(Supracide) 25WP |
0.5 lb/100 gal (TC)
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14
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...PLUS... |
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NARROW RANGE OIL |
0.5–1.4 gal/100 gal
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(415, 440) |
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RANGE OF ACTIVITY: Broad (insects and beneficial
mites)
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PERSISTENCE: Long |
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COMMENTS: For use on all varieties. Reducing the rate of
methidathion 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 40 lb methidathion/acre/season
or 2 applications/fruit year, 45 days apart. May increase citrus red mites. Caution: Serious hazards are associated with oil
treatments to green lemons because of phytotoxicity after sweating; check
label for preharvest interval. For lemons, do not exceed 10 pt/acre or apply
more than once/season when tank mixed with oil.
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| G. |
MALATHION 8 Spray |
1–2 pt/100 gal (TC)
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7
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RANGE OF ACTIVITY:
Broad (insects and beneficial mites)
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PERSISTENCE:
Intermediate
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COMMENTS: For use on all varieties. |
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| H. |
MALATHION 8 Spray |
1 pt/100 gal (TC)
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7
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...PLUS... |
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NARROW RANGE OIL |
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(415, 440) |
0.5–1.4 gal/100 gal
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RANGE OF ACTIVITY:
Broad (insects and beneficial mites)
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PERSISTENCE:
Intermediate
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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.
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UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O’Connell, UC Cooperative Extension, Tulare Co.
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura Co.
C. E. Kallsen, UC Cooperative Extension, Kern Co.
D. R. Haviland, UC Cooperative Extension, Kern Co.
Acknowledgments for contributions to the insect, mite, and snail section:
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
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA
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