Scale insects like mealybugs are among the most common parasites on indoor plants.
They can also be found in the garden at the end of spring, during summer, and in the fall.
Quick scale insect facts
Name – Coccidae, Pseudococcidae, Diaspididae
Lifespan – up to a year (dormant in winter)
Size – from 1/16th to 1/4th inch (1-5mm)
Danger to plant – fatal if infested
Contagious – often
Main treatment – fermented nettle or oil/soap/alcohol mix
The damage they inflict is variable, as are also the shapes they can take to hide.
Identifying scale insects
What do scale insects look like?
They usually have an oval shape, and a hard or soft shell made from special wax. The smallest are 1/16th of an inch (1mm) but some grow as large as 1/4th inch (5mm).
- In particular, mealybugs cover themselves in a white or pinkish velvet that gives the infestation a cottony appearance. It may look like snow or ashes.
- It is also possible to find brown-shelled scale insects that look like small black hulls attached to stems and/or leaves.
There are thousands of species. Each looks slightly different. Some only attack a single plant species while others feed on many different plants.
Symptoms of scale infection
Here is a list of basic symptoms you’ll notice when scale starts spreading on your plants:
Small spots on leaves, leaf joints, stems (especially in hidden areas)- Plant growth slows
- Leaf buds and tips of branches die
- Heavily infested leaves die and fall off
- Leaves are gnarled, twisted, curled and stunted.
- And of course, the plant is overrun with a) small moving bugs and b) fixed spots with bugs underneath them
Different types of scale insects
Since treatments are very similar, usually you’ll only hear people talk about the general term “scale”. But there are actually three major families of scale insects.
- One of these is the famous mealybug. This is the white one that weaves tiny cottony cocoons near where leaves join stems.
- The other two are called scale insects, with the following distinction: armored scale and soft scale, referring to whether the shell is hard or soft.
- Apart from these three families, there are 17 more within the scale insect “Coccoidea superfamily” which totals over 7,000 species.
- There are many more species still to discover and describe, though!
| Main families of Scale insects |
||
| Soft scale | Mealybugs | Armored scale |
| Coccidae | Pseudococcidae | Diaspididae |
| Over 1,000 described species |
Nearly 2,000 described species |
Nearly 2,400 described species |
 |
 |
 |
How to fight scale insects?
Preventive treatment against scale insects and mealybugs
- For inside plants, treat against scale insects from fall until the beginning of spring, 3 to 4 times in all.
Curative treatment against scale insects and mealybugs
- As soon as mealybugs appear, destroy their protective shell with a rag dipped in beer, 90-proof alcohol or soapy water, and then treat with scale insect spray.
- If a major invasion is ongoing, burn or remove all infected branches.
A natural and organic scale insect spray
The best recipe is to mix following ingredients:
- 1 quart (1 liter) of water
- and one teaspoon each dishwashing soap, vegetable oil, 90-proof alcohol.
Spray this solution once a day for 3 to 4 days.
- There are also white oil-based scale insect sprays that have proven their worth.
You can find them in specialized stores. - A spray based on fermented stinging nettle tea is also very efficient in case of mealybug attacks.
It is also possible to slow their spread with a powerful blast of water or by cleaning leaves with a rag dipped in 90-proof alcohol and rinsing afterwards with water.
Take note: it is important to treat quickly, otherwise the pests will completely overrun the plant and it will die.
When do scale insects usually appear?
Scale insects and mealybugs don’t necessarily appear in any given season, but rather emerge when a set of conditions is met. Scale insects like heat and high humidity.
- They can appear all year round on indoor plants.
- Scale is most common in spring, summer and until the beginning of fall in our gardens.
- They cannot develop in winter outdoors, but it is nonetheless best to clear infested areas.
What conditions help them to reproduce?
As we’ve just mentioned, scale insects love heat and humidity.
- They particularly like closed and humid environments, and most of all high temperatures.
- A high relative humidity indoors or regularly spraying water on leaves will accelerate their development.
- Also, the end of spring or the beginning or fall are seasons when temperatures are fairly high and outside air is moist.
Having scale insects on a plant will often lead to other plants being contaminated as well.
What are the risks for the plant?
Scale insects and mealybugs must be dealt with immediately because an onslaught can very well kill your plant.
- The insects feed on the plant’s sap and weaken it.
- This hinders proper plant development and growth, and can even lead to contamination by a black fungus called sooty mold.
- On fruit trees, especially citrus trees, scale insects and mealybugs can compromise the entire harvest. It can even kill a whole tree if they aren’t dealt with early enough.
Often, scale insects also carry diseases from one plant to another.
- This is particularly true for viral diseases and for fungal plant diseases.
Since some scale insects are specific to a single plant or plant family, they actually have value as a form of biological control.
- Experiments are currently underway that use scale insects to fight certain invasive plants.
Plants often attacked by scale insects and mealybugs
Most indoor plants such as ficus tree or hibiscus, orchid, rose, and even succulent-like plants such as Zamioculcas and Aloe vera can contract this pest.
Outdoor plants are also attacked, including citrus, lime tree (or basswood), hortensia, oleander, lilac, olive tree, mulberry tree, red currant, peach tree, and also, albeit less often, the apple tree.
- Note that all citrus species are particularly vulnerable to scale insects.
An efficient and timely treatment against scale insects and mealybugs will help contain spreading to other plants in your house or garden.
Smart tip about scale insects
A regular inspection of your houseplants and garden will help you catch infestations at the start. It’s very easy to contain them early on.
CC BY 4.0: Kim & Forest Starr
CC BY-SA 4.0: Robert Briggs
CC BY 2.0: Katja Schulz, coniferconifer
I noticed mealy bugs all over one of my very large house plants…after really examining it the extent of the damage is quite bad. This plant sits alone far away from any other plants…what are the chances of other house plants getting infected? I don’t usually throw plants away(literally try to save them all), but this one is just covered and stems are sticky and turning brown in places….should I throw this away and cut my losses?
Ha, mealy bugs on a large plant isn’t easy to deal with. Especially if you can’t bring it out for a thorough hosing down because it’s cumbersome. It sounds as though the entire plant has lost its luster. Were you to succeed ridding it of the buggers, as described above, it’ll take a while to recover. The main stems might stay bare since new growth typically comes from the tips, but this depends on the plant species.
To protect your other plants, it’s important to keep a minimum distance of several yards or meters between the “quarantined” one and the others. Mealybugs won’t easily travel that far. They crawl and don’t fly, so for added security you can rest the pot saucer in an even larger saucer, and keep the space between them filled with water as a barrier. However, even more important is to keep a separate set of tools and such: they’re very likely to hitch a ride and spread if you use the same tools. Or you can disinfect them thoroughly before moving on to another plant.
A good compromise it to reduce the plant severely: it’ll be easier to deal with scale on a smaller plant. Or you might throw it all out, and only keep a cutting or two – inspect these very carefully and keep them away from others for the first few weeks.
Hi I have a minature orange tree plant in my conservatory . I noticed some leaves had sticky residue on them . Some leaves had little flies on the underside of then . And also have looked at a photo of different insects they look like Coccidee soft scale . Have got quite a few off . Is there a spray I can get to kill them and keep it bug free . Have used water on a soft cloth .
Hi there Mrs Holden, the little flies might be aphids or whitefly, both also leave a sticky residue on leaves (aphids more so, actually). If in addition to that you noticed soft scale, then it would for sure help to spray. The article mentions fermented nettle, but there are other fermented teas to use. You can make your own, or purchase them in stores ready-made. They’re natural so you needn’t worry about polluting your soil, fruits or plants. And every once and a while, hose all your plants down with water to rinse off any excess product. Even though they might be natural, it doesn’t help when it’s too concentrated. Even just using plain water on a cloth every few days is sometimes enough, as you were doing. It’s important to keep doing it every few days until the infestation is wiped out.
It’s important to know that in a conservatory, pests are at an advantage compared to outdoors: warm temperatures speed their reproduction cycle, less predators, and no wind or rain to knock them off the plant. So in a conservatory you have more work of sorts, but plants also grow better as a trade-off.
Also include neighboring plants in your treatment, since some insects fly back and forth. Since new insects might come in again and again, it’s difficult for plants to truly stay bug-free.
In the long run, the only solution to make sure the pests are fully eradicated is to spread predator insects in your conservatory. They’ll be the ones doing the hunting and pest control in your stead!
My gardener has been treating my hedge for scale for some months and it’s proving extremely stubborn – have You ever heard of water blasting it off a hedge?
Hello Dale, scale insects are a difficult pest indeed. Actually, blasting water at them will succeed in getting most of the invasion under control. Usually a normal garden hose with a tip that concentrates water into a line can do the trick. However, on a long hedge it’s going to take some time: each branch must be splashed and checked for any “leftover” scale insects…
A powerwasher can perhaps help, but only if it can bet set to “not too powerful”. It also depends what type of hedge it is, some are more fragile than others. Always try on a small portion first, and wait three to four days to see if the shrub can take the pressure. Leaves will wilt and drop if they were hurt too much.
Alternatives include fermented teas that also do a great job and are quick to prepare (a couple days).
Thanks heaps
Help my ficus is dying due to an insect disease, I believe is the psila but reading this article could be mealy bugs. The texture of nests are cottony and if touched sticky. I went to a garden centre and they told me to use provado, but is not working at all. My ginseng is dying.
Hi Debora! After sharing with you on facebook, yes, it’s definitely scale insects. I always recommend brushing the bugs off with white alcohol (40% proof at least) dipped in cotton. Check out how to deal with scale insects.
The best article in plant care as far as I am concerned.
Thank you for the information about mealy bugs and brown scale. This is very helpful and works very well. It is amazing how many sites don’t mention this care in their articles.