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Plantwise Technical Factsheet

purple scale (Lepidosaphes beckii)

Host plants / species affected
Agave sisalana (sisal hemp)
Citrus
Elaeagnus
Mangifera indica (mango)
Musa (banana)
List of symptoms/signs
Fruit  -  abnormal shape
Fruit  -  discoloration
Fruit  -  external feeding
Growing point  -  external feeding
Leaves  -  abnormal colours
Leaves  -  abnormal forms
Leaves  -  abnormal leaf fall
Leaves  -  abnormal patterns
Leaves  -  external feeding
Leaves  -  wilting
Leaves  -  yellowed or dead
Stems  -  dieback
Stems  -  external feeding
Stems  -  wilt
Whole plant  -  external feeding
Symptoms
Scale infestation can be seen by the appearance of the purplish brown scale armour on stems, leaves and fruits of host plants. Nymphs and adults suck sap from the foliage and branches and spread to the fruits, causing disfiguration, which decreases market value.

Symptoms are generally related to the severity of attack (population density on host). Damage to fruit occurs in heavy infestations, where spotting and often deformity of fruits affects market value. Areas surrounding scales remain green long after the rest of the fruit ripens. The areas surrounding the scale insects on leaves turn yellow and when severely infested the entire leaf may be discoloured prematurely. Heavy infestation can also lead to leaf fall and leaf and shoot malformation; and in extreme cases, host death. Benassy et al. (1980) noted that young orange trees were not attacked by L. beckii.
Prevention and control
Cultural Control

Dispersal from plant to plant occurs through the activity of crawlers at points where adjacent plants touch. Thus, spread of infected material can be reduced by pruning and allowing adequate spacing between plants throughout cultivation. Mechanical control can be achieved by scraping and scrubbing to remove scales.

Biological Control

L. beckii populations are often controlled by natural enemies. These predator and parasite populations can be disturbed by the use of broad-spectrum insecticides. Insect Growth Regulators used in the control of scales have been shown to disrupt the fecundity and egg viability of Chilocorus sp. (Hattingh and Tate, 1995). Aphytis lepidosaphes is particularly successful at L. beckii control, as this scale is its primary host. Carerro (1980) reported 90-95% parasitism by A. lepidosaphes in some (although not all) orange groves in Valencia since its introduction from France in 1976. Between 1952 and 1968, A. lepidosaphes was used to successfully control purple scale in Texas (USA), Mexico and Greece (DeBach and Rosen, 1991). It is also reported to play a major role in controlling L. beckii populations in Egypt (Abdel-Fattah and El-Saadany, 1979) and Spain (Carrero, 1980). Partial control of L. beckii by A. lepidosaphes was reported in Brazil, Peru, Chile and Cyprus (Debach and Rosen, 1991).

Aphytis melinus, which has been used in the widespread control of the red scale (Aonidiella aurantii), also attacks L. beckii (Debach and Rosen, 1991). A. melinus is documented to be particularly good in citrus-growing areas, where other parasites are vulnerable to temperature extremes and dust (Swan, 1964). Hare and Morgan (1997) report on the mass-priming of Aphytis sp. for biological control.

Aphytis holoxanthus and Aphytis chrysomphali also attack L. beckii and occur extensively throughout the world. Spread of these parasites has occurred as a result of introduction to control the Florida red scale (Chrysomphalus aonidum), and through accidental spread with its hosts. A. chrysomphali is presumed to be native to the Mediterranean (DeBach and Rosen, 1991).

Chemical Control.

Chemical control, where necessary, is usually achieved by spraying with mineral oils at critical points during the season. Mixtures of mineral oils and insecticide (e.g. organophosphates) may be used in control. Benassy et al. (1980) reported that on orange trees in Corsica, A. lepidosaphes was unable to control the pest by itself and that monitoring strategies for determining an economic threshold for chemical treatment were impractical, since by the time different levels of infestation on the leaves could be determined the fruits had also been invaded. They concluded that treatment should be begun as soon as scales are detected, even in small numbers. However, such combinations are highly detrimental to natural enemies, possess high mammalian toxicity and should be avoided except in extreme emergencies.
Related treatment support
Pest Management Decision Guides
UK, CABI; CABI, 2018, English language
 
External factsheets
IVIA factsheets, Instituto valenciano de investigaciones agrarias, Spain, 2015, Spanish language
Department of Agriculture and Food Western Australia Farmnotes, Government of Western Australia, 2007, English language
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