Look closely at a leaf joint and you may find white or pinkish fuzz, like cotton, snow or ashes, or hard brown spots strung along a stem: these are scale insects and mealybugs. Left alone, a heavy onslaught kills the plant, but treat at once and simple organic remedies are very effective.
Scale insects and mealybugs at a glance
Name
Coccidae, Pseudococcidae, Diaspididae
Lifespan
up to a year (dormant in winter)
Size
from 1/16th to 1/4th inch (1-5mm)
They can also be found in the garden at the end of spring, during summer, and in fall. The damage they inflict is variable, as are also the shapes they take to hide.
Scale insects usually have an oval shape, and a hard or soft waxy shell. In particular, mealybugs are covered in white or pinkish fuzz. They look a bit like cotton, snow or ashes.
There are also brown-shelled scale insects that look like black spots on stems and/or leaves.
Symptoms of scale infection
Basic symptoms you’ll notice when scale starts spreading on your plants include:
Small spots appear on leaves, joints and stems
Small spots on leaves, leaf joints, stems (especially in hidden areas)
Plant growth slows
Buds and tips of branches die
Heavily infested leaves 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
When do scale insects usually appear?
Scale insects and mealybugs don’t necessarily appear in any given season. Rather, they emerge when a set of conditions is met. Scale insects like heat and high humidity.
Scale is most common in spring, summer and the beginning of fall. They infect all sorts of shrubs.
They cannot develop in winter outdoors, but it is nonetheless best to clear infested areas.
Keep any newly bought plant away from the others for a few weeks and check the leaf undersides and joints before it joins the collection.
In heated conservatories and greenhouses, winter temperatures often stay high enough for scale insects to keep feeding and breeding rather than slowing down as they would on plants left outdoors.
What conditions trigger scale?
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.
Scale insects on a plant will often quickly contaminate nearby plants, too.
Ants running up and down a stem are a warning sign: they farm scale for its sweet honeydew and chase off the ladybugs and lacewings that would eat them.
Ease offhigh-nitrogen feed on an affected plant, as heavy nitrogen forces soft, sappy growth and is widely linked to larger populations of sap-sucking pests, scale insects among them.
Greenhouses and conservatories combine warmth with still air, so space the pots apart and ventilate.
Will the plant die?
Scale insects and mealybugs must be dealt with immediately because a heavy onslaught can kill your plant.
These insects feed on the plant’s sap and weaken it.
This hinders proper plant development and growth. It also leads to contamination by a black fungus called sooty mold.
On fruit trees, especially citrus, scale insects and mealybugs can destroy entire harvests. It can even kill a whole tree if not dealt with early enough.
→ Did you know? Some scale insect species are specific to a single plant or plant family. These are being investigated for use as a form of biological control against certain invasive plants.
How to fight scale insects?
You can control scale insects through different means. 100% organic and natural solutions exist and can be very effective.
For outside plants, attract beneficial insects: they’ll keep outbreaks from turning into full-blown invasions. If a shrub is overrun, remove and burn all infected branches.
Indoors, 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.
A natural and organic scale insect spray recipe
The best recipe contains these ingredients:
1 quart (1 liter) of water and and one teaspoon each black soap (or dishwashing soap), vegetable oil, 90-proof alcohol.
Spray this solution once a day for 3 to 4 days.
Spray the homemade mix daily for three to four days
→ There are also white oil-based scale insect sprays that have proven their worth. You can find them in specialized stores.
→ It is also possible to slow their spread with a powerful blast of water (as you’d do for thrips) 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.
Plants often attacked by scale insects and mealybugs
Most indoor plants such as the ficus tree or hibiscus, orchid, rose, and even succulent plants like Zamioculcas and Aloe vera can become victims.
Note that all citrus species are particularly vulnerable to scale insects.
An efficient and timely treatment against scale insects and mealybugs will protect other plants in your house or garden.
The three main families side by side
Scale insects fall into three major families, and telling them apart tells you what sort of spray will actually reach the insect underneath.
The three main families side by side
Family
How it looks
Species known
What gets through
Mealybug (Pseudococcidae)
Fuzzy white, weaves cottony cocoons where leaves join stems
Nearly 2,000
Sprays that break through the fuzz; fuzz shields it from ladybugs and lacewings
Armored scale (Diaspididae)
Rather hard shell; once in place it won’t move around
Almost 2,400
Oil-based sprays work through the shell, but not insecticides
Soft scale (Coccidae)
Stays put under a softer shell that won’t break with a crisp sound
Over 1,000
Oil sprays work, but not water-based treatments
The same treatments suit all three because they break through the scale’s protective shells and fuzz.
Different types of scale insects
There are three major families of scale insects. The treatments above work well on all of them because they can break through the scale’s protective shells and fuzz.
The commonest family, cottony where leaves join stems
1 / Mealybug (Pseudococcidae): this is the most common.
It is fuzzy white and weaves tiny cottony cocoons near where leaves join stems.
Its fuzz makes it harder to eat for predators like ladybug and lacewing.
There are nearly 2,000 different species.
Its hard shell stops insecticides but not oil sprays
2 / Armored scale (Diaspididae):
This one protects itself with a rather hard shell.
Once in place, it won’t move around.
Almost 2,400 species have been identified.
Oil-based sprays still work through the shell, but not insecticides.
A softer shell, still beaten by oil sprays
3 / Soft scale (Coccidae):
Like armored scale, it stays put under a shell.
The shell is softer, it won’t break with a crisp sound.
Over 1,000 of these have been documented.
Same: oil sprays work, but not water-based treatments.
There are 17 smaller families within the scale insect “Coccoidea superfamily“, totaling over 7,000 species.
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.
