How to: Treat Your Houseplants for Scale

What is Scale? Scale is a common pest found on houseplants. While there are many species of scale only a few are known to attack tropical plants. Scale belongs to the Coccoidea family and is divided into two groups, the armoured scales and the soft scales. Soft scales are the most common form of scale to infest houseplants. Soft scales are defined by the soft coating surrounding the attached insect.

The most common scale you will find on your houseplants is hemispherical scale and soft brown scale. Both of these scales in the adult form attach into plant tissues; typically leaves and stems. When attached they will lay eggs beneath their bodies and protective coating. The adult will puncture into the vascular tissue of the plant and feed on the phloem. Phloem is essential for plant growth and survival because it transports sugars produced from photosynthesis to the entire plant. When this transport is interrupted it can cause detrimental damage to the plant.

An adult hemispherical scale attached to the leaf of a black corral snake plant. The protective coating can be seen oozing from the site of attachment.
Scale eggs hatch into nymphs or “crawlers”. These nymphs are the only mobile phase of the scale and are very hard to identify. They are called crawlers because they will crawl across the plant until they find a suitable location in which they will attach themselves and develop into an adult. Once attached they release the liquid coating and will lay their eggs. These are always female insects; the males are extremely short-lived and do not cause any physical damage to the plant.

The leaf of a snake plant where a scale insect has attached, laid its eggs and died off. You can see the eggs clearly embedded into the leaf tissue.
How to Treat Scale? Once you have identified your plants has scale you should always isolate it from your other plants to avoid spreading the insects to other plants. The most important step is to remove any leaves or stems with an attached scale. The vascular tissue of this area has already been compromised and will often begin to rot. If the adult was attached long enough there will be eggs embedded in the area. Spray the remaining plant with a peroxide solution that is three parts water per one-part peroxide. You can use any peroxide from the store, most are sold as a 3% solution. Soak all of the plant with this solution, this will kill off any nymphs or “crawlers” as well as any viable eggs you may have missed. The plant should be isolated for another 48-72 hours after being treated. If there are no new spots in that period, the plant is therefore scale free. If new spots appear within this time period repeat the treatment and allow another 48-72 hours observation period.

While scale seems like a gross infestation to have to deal with it is quite simple to eradicate and your plant will be just fine. Make sure if you find scale on one of your plants you follow the appropriate steps to ensure the health of your plants.

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