Scale is a common pest on many houseplants including cacti. The bugs suck sap from the plants resulting in deformities and poor health. Scale on a cactus can be difficult to detect and control as they may blend well with the plant. Accurate identification of the crawler is needed for effective treatment.
As their name suggests, scale are small oval and flat insects in a protective shell-like covering that resembles reptile skin. Their color and shape vary depending on the type of species. You’ll generally spot them on the underside of the leaves or around the joints where stems meet.
Cactus scale appear seemingly out of nowhere but in most cases, they emerge from dormant eggs in contaminated potting soil. Taking your cactus outside during the warm weather season may also expose it to the spreaders like birds and winds. Scale insects are easy to control at an early stage of infestation.
Scale on cactus identification
The scale will appear as flat brown or whitish bumps on the plant’s stems or leaves. A heavy infestation will distort the foliage resulting in spots on the stems, cactus yellowing, and poor growth. Premature drop off of flower buds, stunted growth, and death of stems are also common symptoms of scale on cacti plants.
Some species of scale secrete honeydew, a sugary sticky substance that encourages the growth of sooty mold. This black-colored fungus is not just unappealing, it also reduces the plant’s ability to carry out photosynthesis. Honeydew also attracts ants, bees, wasps, flies, and other sugar-loving insects.
Cochineal scale bugs in particular protect their eggs and larvae in a white cottony fiber making severely infested plants appear like they are covered with a string of popcorns. If you were to remove and rub the white mass on a piece of paper, a vibrant red smear would show out.
How to treat scale on cactus
Cactus scale can be difficult to control as their waxy scales protects them against insecticides or predators. It is also not easy to tell whether the actual insect beneath the scale is alive or dead. A thorough inspection should be done before any treatment to unmask the extent of the infestation.
There are several methods you may use to treat scale on cactus.
1. Use rubbing alcohol
Isopropyl alcohol is highly effective against scale, mealybugs, fungus gnats, spider mites, and other crawlers. To treat the scale, dip a cotton ball or swab into full-strength rubbing alcohol and manually dab the visible pests. Rubbing alcohol will dissolve the protective coatings on the insects causing them to dehydrate and die.
You may also make a rubbing alcohol spray and apply it to treat the scale. Mix 1 part 70% rubbing alcohol with 10 parts water in a spray bottle to form a solution. Alcohol that is too concentrated may burn or kill the plant. Spray on a small part of the infected plant and wait for a few days to watch for any signs of alcohol burn.
If you don’t see any reaction on the plant, spray the entire plant making sure that all the pest-infested parts are well-soaked. Allow the rubbing alcohol solution to act on the pests for about five hours then rinse it from the plant with clean water. Repeat the treatment weekly until all the pests are gone.
2. Apply insecticidal soap
Soap makes an effective insecticide but high concentration may kill or damage the plant. However, there is commercially available insecticidal soap formulated to minimize potential plant injury. To get rid of the cactus scale, simply mix and apply the soap solution as directed on the product label.
Insecticidal soaps are chemically similar to certain brands of household detergents and liquid hand soaps. Through experimentation, many gardeners have successfully used homemade soap sprays in controlling bugs on plants but the risk of damage is greater.
Due to a short residual action, soap sprays must be applied severally at short intervals to completely kill the scale and other crawlers. Also, you need to apply thoroughly on the plant parts completely covering the insect’s body, explains the University of California Cooperative Extension.
To avoid contaminating the soil or overwatering the cactus, be sure to cover the pot with a plastic sheet before drenching the plant in the soapy spray. Use distilled water in mixing the soap spray and apply when the temperatures are cool. The use of hard water and rapid drying may decrease the effectiveness of the soap spray.
3. Apply neem oil
Neem oil is one of the most effective agricultural oil used in the treatment of plant pests. It primarily kills the plant crawlers by smothering. To use, mix it with water as directed on the product label and spray directly on the insects, completely covering them. Repeated applications are needed for the complete removal of scale.
4. Biological control
There are few predatory and parasitic options that can help in controlling scale insects on your cactus but they are commonly effective in outdoor settings. Lady beetles, parasitoid wasps, and green lacewings are popular destroyers of scale, aphids, and mealybugs on plants. They are commercially available and commonly used in large fields and greenhouses.
Unfortunately, the biological control approach may not work when a large amount of scale is present, explains Colorado State University. Additionally, there are no reliably effective predators available to control scale indoors. Moving your houseplants outdoors may be necessary if you opt to use this approach.
5. Cultural control
If you suspect scale insects on your cactus, quarantine the plant to prevent the bugs from spreading to other plants. Examine the plant and prune the diseased areas and destroy them. Wash off the plant in clean water or carefully wipe off the stems with a soft damp cloth. Then repot the plant in fresh succulent soil.
Cacti are incredibly hardy plants with great resistance to pests. The plant can easily recover from scale if treatment is done in the initial stages of the infestation. Regular inspection of plants is very important as it helps in discovering any problem before it becomes a threat to the plant’s health.
My name is Diane M Lewik, and I am the founder of this website. I am a degree holder in plant biology from the University of California – Berkeley. Over years, I have cultivated a vast collection of succulents and I have learned a great deal about how to grow and care for these unique plants.