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How to Manage Pests

UC Pest Management Guidelines


Purple scales; one with parasite exit hole.

Citrus

Purple Scale

Scientific Name: Lepidosaphes beckii

(Reviewed 7/03, updated 7/05)

In this Guideline:


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)**  

A. NARROW RANGE OIL# 1.2–1.4 gal/100 gal (TC) 4 hours
  (415, 440)    
  RANGE OF ACTIVITY: Broad (unprotected stages of insects and mites)
  PERSISTENCE: Short
  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.
       
B. CHLORPYRIFOS*    
  (Lorsban) 4EC 0.5–0.75 pt/100 gal (TC) See comments below
    ...or...  
    6–12 pt/acre (LV)  
  RANGE OF ACTIVITY: Broad (insects and beneficial mites)
  PERSISTENCE: Intermediate
  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.
       
C. CARBARYL*    
  (Sevin) 80S 1–1.2 lb/100 gal (TC) 5
  RANGE OF ACTIVITY: Broad (insects and beneficial mites)
  PERSISTENCE: Long
  COMMENTS: For use on all varieties. Do not apply during bloom or exceed 25 lb/acre/application. May increase citrus red mite populations.
   
D. CARBARYL*    
  (Sevin) 80S 0.4 lb/100 gal (TC) 5
  ...PLUS...    
  NARROW RANGE OIL 0.5–1.4 gal/100 gal  
  (415, 440)    
  RANGE OF ACTIVITY: Broad (insects and beneficial mites)
  PERSISTENCE: Long
  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.
   
E. METHIDATHION*    
  (Supracide) 25WP 1 lb/100 gal (TC) 14
    ...or...  
    12–16 lb/acre (LV) 60
  RANGE OF ACTIVITY: Broad (insects and beneficial mites)
  PERSISTENCE: Long
  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.
   
F. METHIDATHION*
  (Supracide) 25WP 0.5 lb/100 gal (TC) 14
  ...PLUS...    
  NARROW RANGE OIL 0.5–1.4 gal/100 gal  
  (415, 440)    
  RANGE OF ACTIVITY: Broad (insects and beneficial mites)  
  PERSISTENCE: Long  
  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.  
     
** TC - Thorough coverage uses 1,000–3,000 gal water or more/acre, depending on tree size.  
  LV - Low-volume uses 20–100 gal water/acre.  
+ Minimum days before harvest takes into account the California restricted entry interval and the federal preharvest interval and lists the longer interval. (See Table 1 Mandatory Intervals Between Application, Reentry and Harvest, and Hazards to Bees.)  
* Permit required from county agricultural commissioner for purchase or use.  
# Acceptable for use on organically grown produce.  

[Precautions]

PUBLICATION

[UC Peer Reviewed]

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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Statewide IPM Program, Agriculture and Natural Resources, University of California
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