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How to Manage Pests
UC Pest Management Guidelines
Citrus
Purple Scale
Scientific Name: Lepidosaphes beckii
(Reviewed 7/03,
updated 7/05)
In this Guideline:
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DESCRIPTION OF THE PEST
Purple scale is one of the armored scales. The cover of the adult female purple scale
resembles a mussel shell in shape. The immature male cover is shorter and much
narrower than the female cover. Mature males are winged insects that search out
the immobile females. After mating, females lay 40 to 80 eggs under the cover.
After egg hatch, crawlers emerge from under the cover and settle on branches,
twigs, leaves, or fruit and begin to form their covers. They are covered with a
mass of waxy threads until about half grown; at that time a brown cover with a
purplish tinge forms. Purple scales prefer the cooler, shady parts of trees;
temperatures above 80°F (27°C) greatly reduce a population. Two generations
occur between May and October and a third may be partially completed before
cold weather starts.
DAMAGE
Purple scale is an occasional pest in certain coastal areas where
the mild climate and humid conditions favor its buildup. It attacks all parts
of the tree. Its feeding causes yellowish halos to develop on leaves; on young
fruit the feeding sites remain green. When populations are high, defoliation
and twig dieback can occur; this usually takes place in limited patches on the
lower north side of trees.
MANAGEMENT
Parasites usually provide good control of purple scale. Biological
control may require supplementary treatment at times, especially on dusty trees
next to dirt roads.
Biological Control
The most effective purple scale parasite is Aphytis lepidosaphes, a parasitic
wasp that is generally distributed in areas where purple scale occurs. This
parasite develops externally on the body of immature scales under the scale
cover. Because this parasite is not commercially available, conserve naturally
occurring populations of this beneficial in the grove. If treatments are
necessary, during August and September either spot treat (i.e., treat only
those trees with high populations of purple scale) or treat every fourth to
sixth row at a 4- to 6-week intervals if the entire grove is infested. This
will assist in preserving natural enemies.
Several predators including the twice-stabbed lady
beetle, Chilocorus spp., and the Australian lady beetle, Rhyzobius
(Lindorus) lophanthae, are important.
Organically Acceptable Methods
Biological control and petroleum oil sprays are acceptable for use on
organically certified citrus.
Treatment Decisions
If a treatment is needed, it may be sufficient to spot treat (i.e.,
treat only those trees with high populations of purple scale) with an oil spray
or wash dusty trees with water. Oil sprays for the California red scale also
control the purple scale.
| Common name |
Amount to Use |
Minimum Days before Harvest+ |
| (trade name) |
(type of coverage)** |
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| A. |
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: Apply higher rate of narrow range oil in July or
Aug. only. 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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| B. |
CHLORPYRIFOS* |
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(Lorsban) 4EC |
0.5–0.75 pt/100 gal
(TC)
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See comments below |
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...or... |
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6–12 pt/acre (LV) |
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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; however, it may cause
ridging in lemons. Apply thorough coverage spray in 1,200–1,600 gal/acre; do
not apply during daylight hours of bloom period or exceed 12
pt/acre/application or 15 pt/acre/year of chlorpyrifos; no more than 2
applications/fruit year, and no closer than 30 days apart. Minimum period
before picking is 21 days for up to 7 pt/acre and 35 days above 7 pt/acre. Do
not apply during Dec., Jan., or Feb. See label for additional restrictions.
Rates greater than 8 pt/acre are allowed only in Fresno, Tulare, Kern, Kings,
Stanislaus, and Madera Counties.
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| C. |
CARBARYL* |
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(Sevin) 80S |
1–1.2 lb/100 gal (TC) |
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 apply during bloom
or exceed 25 lb/acre/application. May increase citrus red mite populations.
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| D. |
CARBARYL* |
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(Sevin) 80S |
0.4 lb/100 gal (TC) |
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. 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. Some California red scale population resistance in San Joaquin Valley;
also resistance in some Euseius tularensis populations. 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 |
1 lb/100 gal (TC) |
14 |
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...or... |
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12–16 lb/acre (LV) |
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 sprays, which
are available under a Special Local Needs permit. May increase citrus red
mite populations.
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| F. |
METHIDATHION* |
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(Supracide) 25WP |
0.5 lb/100 gal (TC) |
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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![[Precautions]](/IMAGES/btn-precautions_bul.gif)
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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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