SCALES

 

 

    Scales, though closely related to mealybugs, differ in possessing a hard shell or covering rather than the soft, waxy filaments. Scales are usually sedentary when mature and do not move over the foliage as do mealybugs. Scales are usually small and inconspicuous and by the time an infestation is noted, the population is usually so great the plant is unsalable. In a general scale life cycle, eggs are produced beneath the female shell and hatch into tiny crawlers which are invisible to the unaided eye. Crawlers are not covered by a hard shell and they migrate to newly expanded foliage, finally settling near leaf veins on the underside of leaves or stems. It is this crawler stage, which is practically impossible to detect on cuttings or other propagation material, that is responsible for spreading the infestation. There are many pests of tropical foliage plants. Hemispherical scale, shown here infesting lower leaf surfaces of Aphelandra, is one of the most common.

 

    The Japanese wax scale is often found on Podocarpus, but also occurs on other foliage plants.

 

    The brown soft scale is a common greenhouse pest and readily occurs on Pteris ferns, as well as other foliage plants.

 

    The false oleander scale, shown here infesting areca palm, is also a serious pest of parlor palm as well as numerous other palms. The yellow streaks in the foliage which appear to radiate from the scales are feeding injuries and are typical of injuries caused by this pest on palms.

 

    The Florida red scale, here infesting English ivy, is another common and serious pest.

 

    The actual number of tropical foliage plants attacked and seriously damaged by scales is too numerous to list in this presentation. However, as a indication of the wide variety of foliage plants attacked, note as illustrated by this slide the severity of the latania scale infestation of bromeliads.

 

    Also, note the heavy infestation of cactus scale which can be found on numerous ornamental cacti.

 

    Another injurious scale, which is named for the group of plants it attacks, is the fern scale shown here infesting staghorn fern. The brown individuals are the female scales and the white forms are males. The fern scale also is quite damaging to asparagus, birdís nest and Nephrolepis species of ferns.

 

   Generally, aphids, mealybugs and scales are effectively controlled by the same pesticides. Research has shown the products listed here are effective when properly applied at effective concentrations: Cygon, Meta-systox-R, Orthene, Furadan, Diazinon, Vydate, Temik and Enstar. Control of mealybugs and scales is especially difficult as the waxy deposits and shell-like covering protects these pests from exposure to the pesticide. In these cases, chemicals that are systemic (within the plant) and which the pest obtains during feeding are more effective than chemicals that are toxic only when in actual contact with the pest.

 

    Also, note that even after control of these pests, the waxy deposits, as shown here on Dracaena marginata, as well as dead scales tend to remain attached to foliage and continue to make the plant appear unsightly. Certain scale infestations are accompanied by sooty mold development. Ideally then, control is needed before infestations become too severe and it is imperative to maintain stock plants scale and mealybug free.

 

    All newly acquired plants should be quarantined in your greenhouse, shop, etc., followed by careful and frequent inspection for living pests. This is especially important with plants used for interiorscaping.

 

    A very important problem in scale control is determining whether or not a scale is alive. This can be readily determined by lifting the female shell or covering using the point of a knife. If the scale is firmly attached to the leaf of stem surface or if the cover pops off revealing a yellow-orange, plump mass beneath the cover, as shown here, consider the scale alive.

 

    However, if the shell is completely removed from the leaf surface, as illustrated in this slide, or a dried mass is found beneath the cover, the scale is probably dead. As a word of caution, however, remember that scales that have died may cover viable eggs, also shown here beneath the removed scale. These eggs will hatch and can continue the infestation. This is one reason why repeated chemical treatments are necessary for complete control.

 

    At times strange looking structures are detected on foliage that are mistakenly identified as scales. This slide is not an insect, insecticides are of no use against this problem. Therefore, be certain of the real cause of your problem before attempting any control actions.

 

     More information on scales can be viewed at "Insect and Related Pests of Flowers and Foliage Plants". Click here to go there now!

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Lance S. Osborne: lso@mail.ifas.ufl.edu
Copyright © 2000 [University of Florida, MREC]. All rights reserved.
Revised: February 23, 2005.