Vivi's Orchid Corner
July 2000 - Volume 5, Issue 6
"SCALES"
Dear Orchid Friends:
Scales… pesky and hard to rid. Orchid lovers cringe if scale is found on any of their plants. Your best defense is to inspect your plants constantly. Scales are difficult to detect due to their inconspicuous nature.
How does one know whether scales are present? Generally, you notice symptoms related to having scale versus the scale itself. Perhaps you notice a slight yellowing of your plant or think "it just doesn’t look right." Another time you note the presence of ants on a plant. Then, after closer inspection, scale is noted on the underside of a leaf or in the folds of a psuedobulb.
Scale insects attack plants by attaching themselves with their long stylets or proboscis and feeding on plant nutrients. Scales are generally known as sucking insects. After attaching themselves to the plant, the scales secrete a sap or honeydew. This sweet sap attracts ants and increases the risk of developing black sooty mold. Some mature scale insects develop a protective covering or armor which makes it more difficult to rid of their infestation.
Scale insects are divided into two general kinds: soft scaled and armored. The soft scales secrete the honeydew sap while the armored scales develop the hard protective covering. Both kinds are sucking insects. Immature scale of both kinds are all free moving, which means they crawl over and to other plants. Mature scales attach themselves to the plant and remain in place. Scales are tiny… which is why it is hard to notice them.
There are several species of the soft scales: Brown scale (Coccus hesperidum) and Orchid Pit Scales (Asterolecanium epidendri) are the most common. Brown scales are a yellowish - tan color and are approximately 1-3 mm long. Pit Scales leave pits in the plant and have a somewhat waxy covering. Orchid Pit Scales are more circular in shape and are approximately 1.5 mm in diameter. Armored scales live under the comfort of their protective coating. Armored scales are circular to oblong shaped. The most injurious of these armored scales is the Boisduval Scale (Diaspis boisduvalli). Females have a greyish white shell. Males form clusters of cottony webs usually on the undersides of the leaves. A few other armored scales include: Florida Red Scale (Chrysomphalus aonidum), Proteus Scale (Parlatoria proteus) and the Vanda Orchid Scale (Genaparlatoria psuedapidiotus).
Some scale insects also inject a toxin into the plant in addition to sucking the nutrients. This is definitely adding insult to injury! Scale can cause spotting or yellow chlorotic areas on the plant. Leaves have a yellow mottled appearance. The plant may appear withered or dehydrated.
How do you treat scale? Remove old sheathing from the psuedobulbs and observe for scales. They love to hide. Check the folds and undersides of the leaves. Consistent and diligent observation of your orchids is key to preventing and ridding of any infestation. Several pesticides can be used: malathion or oil sprays. Spraying your plants regularly can control infestation. It may require several applications over a period of time to completely rid of scale. Manually removing scale and scrubbing your plants is better for a smaller collection. Dipping a toothbrush into malathion solution and scrubbing the scales off is effective but more laborious. As with all pesticides, protect yourself and your environment. Rubbing alcohol (isopropyll alcohol 70%) surprisingly is an effective method to control scale. Dip your Q-tip or clean toothbrush in rubbing alcohol and scrub scales to remove them from the plant. Use a clean Q-tip on each plant or more often as needed. Rubbing alcohol does have drying properties, but is far less toxic to plants, humans and the environment.
Scales are difficult to eliminate. Diligence is necessary because they reproduce rapidly and the immature scales are so mobile. Wash, rinse and observe. Keep your plants, tools and growing areas clean. Remember to contain your infected plants to one area to help reduce the risk of spreading. Insects generally are more active in warmer months. Carefully inspect any new plants you purchase and keep them separate from your other collection for a short while.
Prevention is key. However, scales can be controlled with a little perseverance.
P.S. Enjoy the Summer!
Until next time,
Vivi
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Bemvindo Brasileiros!