The formerly gorgeous green and lush leaves of your houseplants are yellowing, stunted, or even becoming deformed. Brown pockmarks appear in lines and groupings on your plant’s foliage, and you notice leaf drop. Oh no! What could be happening?
The symptoms described above could mean that your plant has “scale”. While the term sounds like a disease, it is actually an infestation of tiny insects that adhere to the stems, branches, or leaves of your houseplant, where they live on the nutrient-rich sap found there. The name for these tiny pests (Scientists have identified more than 7,000 species of Scale) comes from their tendency to form a waxy or shell-like exoskeleton that protects the insect body.
What is Scale?
Scale varies in color, shape, and size, depending on the insect, but is most often small, brown, round or oval, shell-like bumps running in groups along the stems and leaves of your plant. The rounded mounds, or domes, are hardy, tiny insects. Hundreds of eggs are laid beneath the female’s scale. In large infestations, live young are produced under the scale. Scale almost always appears in groups or clusters because the fecund females lay so many eggs, which survive prolifically. When the eggs hatch, the baby insects, called “crawlers”, move along the plant, find a protected place to lodge, and begin to form a shell. The life cycle of a Scale can be up to ten weeks, so these tiny pests have great potential to wreak havoc on your houseplants.
Pic: Hawaii Master Gardeners
There are two types of Scale: armored or hard scales; and unarmored or soft scales. A protective waxy substance covers soft scale insects. Their more penetrable exterior makes them somewhat easier to eliminate with the use of pesticides. Hard Scale is difficult to eradicate because the animal’s tough shell protects it from insecticidal soap, horticultural oil, or other sprays.
How do I know if my plant has Scale?
Beyond the presence of bumpy, round, and colored groupings on plant parts, you might also notice a sticky substance and a sooty, black mold that spreads on the underside of leaves. This is because scale insects produce a sugary honeydew when feeding on the plants. The honeydew attracts fungal organisms that excrete sooty mold, one of the most visible indicators of Scale.
Photo by Dan Gill/LSU AgCenter
How do I treat Scale on my houseplants?
Before you start eradicating Scale, you should immediately quarantine the infected plant.
Removal of Scale is challenging. You have to either scrape off the waxy or hard shells or catch crawlers before they settle and begin to form their own hard surface.
You can remove hard scales by wiping the plant with a clean cotton pad or cotton swab and rubbing alcohol. Alternatively, you could try using your fingernail, tweezers, or even a toothbrush. However, this could damage the delicate structure of the plant stem or leaves, so you need to be careful. If you have so many Scale that removal seems impossible, you may want to discard the plant as it could infect others in your collection.
Once you’ve removed the Scale, use an insecticidal soap or horticultural oil to kill any crawlers. Spray the entire plant from top to bottom with the soap or oil, then wipe foliage clean with a soft rag or paper towel. Dispose of the towel immediately. Please note insecticide should be applied in the evening or away from direct bright light. The reflection of light on the oil could burn your plant’s leaves.
You will need to repeat the insecticidal soap or horticultural oil application weekly with diligence to catch any remaining crawlers. To prevent future infestations of Scale, ask one of the experts in our Houseplant Haven about systemic indoor plant insecticides.
If you have any questions about the appearance of Scale on your houseplant, we’re here to help! Please do not bring your plant to the store. Take a photo of your plant, including the area of concern, and bring the photo to our store or attach it in an email to [email protected]
Natria RTU Insecticidal Soap
Kills insects in minutes. Great for indoor and outdoor use. Use for organic gardening.
Neem Oil RTU
32 OZ. Ready-To-Use Neem Oil Spray is an all-purpose insecticide, miticide, and fungicide for organic gardening. It is derived from the Neem seed that is safe to use on roses, flowers, vegetables, herbs, spices, houseplants, trees, turf and shrubs. Kills all stages of insects including eggs, larvae, and adults. Active ingredient: clarified hydrophobic extract of neem oil 0.9%
Bonide Oil Spray All Season QT
A superior type paraffinic oil that may be used as a growing season spray, dormant spray (no leaves) or delayed dormant (green tip) spray to control over wintering eggs of red spiders, scale insects, aphids, bud moths, leaf roller, red bug, codling moth, blister mites, galls, whitefly, mealy bugs and other insects. Highly recommended for use on fruit trees, shade trees, shrubs, ornamentals, roses and vegetables. Now labeled for disease control.