There is nothing more frustrating than discovering that one of your favourite houseplants has become the main course for a pest. It’s even further infuriating when the plant in question is very large, making it that much more difficult to deal with unwanted guests. And it’s absolutely maddening when the pest in question is scale. I shudder just thinking about it.

There isn’t any houseplant grower that doesn’t loathe these insects and seek out to destroy them with a vengeance before the infected plant is reduced to nothing. If you’ve ever found the hard shell of a scale insect stuck to a glossy leaf of a cherished plant, you know exactly what I’m talking about. Even the most dignified plant growers are reduced to insecticidal maniacs when scale insects are discovered.

Unfortunately these insects are a common pest of houseplants that we unintentionally bring home with us, usually when we don’t thoroughly inspect newly-purchased plants. I believe that greenhouses and florists should be held accountable for selling infested plants therefore I advise shopping at reputable places that offer a money-back guarantee or a reasonable exchange policy. After all, professional places should be selling healthy, pest-free specimens. But because insects can be quite inconspicuous, sometimes even the most well-intentioned garden centers can sell a ‘lemon’ no matter how sincerely hard they work at avoiding it. So it’s equally as important for the consumer to shop wisely by giving a potential purchase a thorough inspection. If the plant being examined isn’t given a clean bill of health right from the start, it’s best to leave it behind.

So it’s prudent to shop smart. But what if it’s not a newly-purchased plant that you can return to the retailer? What if you notice something suspicious on one of your long-standing plants, lean over to take a closer look and discover - horror of horrors - scale?! What happens next? Aside from the string of profanities that spew from your lips.

There are really only two choices when one of your plants is attacked by this vile parasite that is very difficult, sometimes impossible, to eradicate. 1) Wage war or 2) Toss the plant out of a ten-story window (not literally, although it is tempting). The decision is yours to make. For me, it all depends on whether the battle is worth fighting. If the plant is cherished, I make an honest effort to rid it of problems before destroying it. If the plant is a common one that can be readily replaced and it has no special place in my heart, I fling it as far as I can before it infects any other plants.

If you decide to wrap up your problem in a green garbage bag and toss it to the curb, there’s no need to go any further. But if you’re eager to wage war on the scale insects that are stunting and deforming your precious plant, read on. Regardless of whether you win the war, you’ll learn a little about these buggers, at the very least. But no matter what anyone says, I believe that you can win the war with scale if you are persistent. They are a tough lot to beat but they are not immortal.


What Are These Evil Things?

There are thousands of species of scale that differ greatly in color, shape and size. These round or oval insects, related to aphids, come in colours that range from tan to brown to black. This group of troublesome bugs - varying from 1/16 to 1/8 inch in diameter - resembles bumps and is often initially mistaken for a disease instead of a critical infestation.

Usually found on stems, the underside of leaves and sometimes even on leaf tops, their numbers can increase rapidly. Since a considerable portion of plant owners do not inspect their greenery regularly, scale will go undetected for a long time. By the time it is discovered, the population will have grown to significant numbers, capable of severe damage to the infected plant(s). This critical discovery will leave any grower wondering whether it’s worth battling such a sizable infestation (or whether it’s wiser to just kick the infested plant to the curb and replace it with another).

Scale insects are generally divided into two groups: soft and armored. Soft scale – covered by a protective waxy substance - is slightly easier to kill as opposed to the armored latter, which constructs a hard shell over its body, making it (almost) impenetrable.

Scale live under their tough shells and feed on the plant while laying eggs for the upcoming generations. Adults are stationary but juveniles (crawlers) have legs and are quite mobile. Not only can they crawl but they're also strong enough to drop off a plant and move to another. Along with dropping and walking, they also won’t hesitate to hop over to the next plant whose leaves touch their current territory.

They’re not in a hurry to get to their destination when they do decide to drop. They can survive several days without food while they travel from plant to plant searching for a place to call home. Once they find that perfect spot, they stick their mouth into a leaf or stem, tuck their legs under and start building a protective shell. Once they're settled and the shell is built, they lose the legs and spend the rest of their lives there.

But they don’t always move to new homes on their own; they also hitch rides with humans who often spread the insects from unlucky plant to unlucky plant via their hands and clothing. In addition, they get tossed onto other plants by strong currents, by feather duster taxi rides and by being blown in through the window by strong winds – perhaps from your neighbour’s yard!


The Damage They Do

Although seemingly motionless once they reach adulthood, scale insects are always hard at work under their protective shells. Latching onto a plant, and typically locating themselves along a central vein where the meal is the sweetest, these critters will insert a slender stylet into plant tissue (where it remains permanently) and suck plant juices all day, every day. It’s not an exaggeration to say that they drain the life out of your plants. Literally.

As sap is withdrawn and vital fluids are lost, the host plant will begin to weaken. Damage includes delayed, poor, stunted or curling new growth, discoloration, yellowing foliage, premature dropping of leaves and noticeable wilting. How bad can it get if scale is not caught in the early stages? Death of the plant. Severely infested plants usually don’t stand a chance.

But even as symptoms begin to arise, it’s usually the sticky, shiny mess on the plant, the floor around it and even on nearby furniture that finally draws attention to an infestation that is quite large at this point. That sweet liquid named honeydew, which is excreted by scale because they can’t metabolize all the sugar they ingest, can also attract ants and other pests that are addicted to it. If you notice ants – that have quite a sweet tooth – suddenly hanging around your plant(s), you may have scale (or aphids). The honeydew also encourages sooty mold, a black fungus.

The presence of a few scale pests is not the end of the world, nor will a couple of them here and there kill your plant. Unfortunately, if left to their own devices, those few scale will multiply like rabbits into many little scale that will grow up to be adult scale and make more little scale that will grow up…. You get the picture. The population multiplies quickly and explodes in numbers. A full-blown scale infestation is something you never want to experience so check your plants regularly.

But if misfortune strikes and the battle is worth fighting, control measures must be taken (yesterday) swiftly. So what’s next?


Taking Action Against This Parasite

When you prepare to battle scale, you have to adopt the bulldog mentality and be extremely persistent. Do not leave any survivors; annihilation must be total. A scale or two left behind can propagate to dozens within no time. This insect population multiplies rapidly into overwhelming numbers until there are a gazillion of these tiny monsters all over the host plant (and inevitably all over many other favored foliage).

First and foremost, move the plagued plant as far away from the rest of your greenery. Isolation will help curb any further infestations by an insect that is very invasive. Search for an appropriate spot that your plant can stay in for a few weeks. Treatment of scale is a long-term process that will require repeat applications in order for it to be successful. Your ailing plant won’t be heading home any time soon so make it comfortable. And remember to wash your hands properly after handling infected plants. You can move an insect-infested specimen to another town and still end up with a major plague throughout an entire group of plants in your home by not washing up. Your hands are very often the reason insects end up on other plants.

Winning the war with scale will depend on how successful you are in eliminating the insects you can’t see. The invisible monsters are the ones that will continue to breed. The good news is that the scale pests that are barely visible without magnification are more vulnerable to treatment than the stationary adults. They are the juveniles or ‘crawlers’ that have legs and are quite mobile – but they have not yet developed the tough armor (wax shell) that encases them and repels water, water-based insecticides and many pesticides. Without a protective coating, the young insects are vulnerable to insecticidal treatments like any other soft-bodied pest. So with that in mind, as soon as you’ve dealt with the adults, deal with the juveniles quickly, before they build their shells.

But first things first..the adults that make more scale babies...

The first thing I always recommend whenever a plant is attacked by insects is to give it a shower (in the bathtub or sink) to knock off as many pests as possible. After the thorough rinsing, manually remove as many mature scale as you possibly can by scrubbing them off with a soft toothbrush or with the brute force of a fingernail. Use rubbing alcohol - always a good treatment choice - to strip away the wax from the shells and dehydrate the insects. Dip a cotton swab in alcohol, touch each insect with it and then wipe it away. Repeat this process until you can no longer see any signs of adult scale. (Note: This is an easy application for smaller, large-leaved or lightly-infested plants but it is much too tedious for bigger specimens and severe infestations. For the bigger jobs, skip the cotton balls and head straight for the spray bottle.)

After the cotton swabs, fill up an inexpensive spray bottle with one part (70% isopropyl) rubbing alcohol to three parts water. Spray the infected plant thoroughly, paying particular attention to the nooks and crannies where scale successfully take refuge from the alcohol attack. For the extermination to be successful, the alcohol mix must make direct contact with the bugs, so spray away till the plant is absolutely drenched! Repeat this treatment every 3 – 4 days for several weeks to make sure no ‘crawlers’ get away. (Note: Keep the plant out of the sun during treatments.)

You must bear in mind that you cannot treat your scale-infested plant only once and expect that the problem is solved. Young insects are champions at hiding, and usually too small for the naked eye to detect, so it’s easy to miss them with only one extermination application. If you don’t heed this advice, they will materialize once again with a whole new generation and the nightmare will start all over again. Several treatments must be applied before you can put your feet up. If possible, inspect your plant daily (in a bright area), or at least every other day, by picking it up and checking underneath the leaves, up and down the stems and in between leaf axils.

The spray method is more efficient and effective than simply wiping with cotton swabs since it’s more likely to make contact with the demons that go into hiding. In addition to the alcohol, some plant owners add a few drops of mild dishwashing liquid to the mister. You can also choose to use insecticidal soap for the juveniles since they are very vulnerable without their protective shells. Because there are several types available, read the label before purchasing to make sure that scale are included as part of the list of insects that the product will be effective against. Alcohol can also be combined with insecticidal soaps. Mix up an alcohol-insecticidal soap spray by substituting alcohol for half the water required for the dilution recommendations on your product’s label.

After several treatments, and careful inspection, if your plant is showing no signs of scale, you can safely place it back in its usual home. Check your plant weekly after that to catch any possible scale reappearances in the early stages.



Persistence is the name of the game with scale infestations. If you are diligent, treat the plant several times with the alcohol mix and check it regularly for signs of trouble, you can win the war. Of course, this also depends on the magnitude of the invasion. Small outbursts can be dealt with, and usually eliminated. But what about those dreadfully sizeable ones? My advice? Unless the potted plant is valuable, toss it before scale sweep through your entire collection and you end up with a major epidemic in your home. Then run out to the greenhouse and treat yourself to a new plant. As a way of consoling yourself, of course.


Photographs by: James Solomon, USDA Forest Service, United States
Photos are posted at: www.insectimages.org

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