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The 30 Year Mealybug Infestation: a Horror Story

These new houseplants may come from a reputable nursery, but that doesn’t guarantee they’re not infested with mealybugs or scale.

Where do the unwanted insects found on our houseplants come from? Some come indoors all on their own (spider mites are so small they can pass right through a window screen) or by clinging to our clothes when we work in the garden. Some are blown indoors by the wind when we open a door. But others arrive by hitchhiking on the new plants and cuttings we bring into our homes.

That’s the case with mealybugs and their equally sneaky cousins, scale insects. Female mealybugs and scale insects can’t fly, nor can those species that infest our houseplants survive in our outdoor gardens, at least not in cold climates. They only live on other houseplants. So the one way for mealies and scale insects to reach your houseplants – assuming you agree that it has been proven that spontaneous generation just isn’t possible – is through an infested plant or cutting.

Mealybugs are brought in on infested plants or cuttings.

I also regret to inform you, in case you didn’t already know it, that mealybugs and scale insects can be found in the very best, most reputable plant nurseries. Such places make a valiant effort to keep them under control, but since they’re constantly bringing in new plants and can’t inspect each one, errors happen. And it takes only one stray mealie or scale insect to produce thousands more.

My Sad Story

A simple dieffenbachia led to 30 years of infestation.

In my case, my mealybug infestation started with a simple dieffenbachia I “saved” from the compost pile out behind my local botanical garden (hmm… I wonder what it was doing in said pile!). It was the source of an infestation that lasted 30 years!

I made the error of not putting it quarantine, proudly setting it among my other houseplants. When I finally noticed it was infested (mealybugs can be very surreptitious), several of my others plants were too.

Well, I treated those plants, sometimes again and again, using various products. I tried soaps, oils, rubbing alcohol, putting the plants outside in summer, etc., each time apparently with some success… only to discover later that the mealies were back, usually on the same plant I was so sure I had thoroughly treated, but also elsewhere. I kept up this game of treating infested plants on a per case basis for 30 years (I’m a slow learner), even, out of frustration, treating every single plant on more than one occasion and that was quite a job. It never worked: the bugs always came back.

Scale insects on the stem of Cornus sanguinea
Scale insects

At some point in time (probably various points in time), scale insects also joined the fray. I actually found several species of them, some strictly on certain plants (orchids, bromeliads), others more generalized. I applied much the same treatment as for mealybugs with much the same results.

In the back of my mind, I knew the right solution: you don’t treat mealybugs or scale, you throw way the infected plants. But with a collection of some 600 plants, some very precious to me, I was just unwilling to face that fact.

5 years ago, though, I decided that enough was enough and I did it. I tossed out all the infested plants, even ones that I knew I would never be able to replace. That wasn’t enough: I have soon found others that were infested. I tossed them too. Then tossed even more. But at least the numbers of infected plants kept diminishing. For 2 years, I still kept occasionally finding infested plants, but I stuck to my guns and threw them out as well. By then, my houseplant collection had dropped by nearly half: nearly 300 plants ended up in the garbage. But eventually my perseverance paid off: I haven’t seen a single mealybug or scale insect in 3 years now. If I do, though, you can bet the plant is it found on will go straight into the garbage.

What I Should Have Done

You can use a plastic bag to isolate your plants.

What I should have done from the start, and now do religiously, is to always isolate (quarantine) any new plant or cutting I bring home, whether I purchased it, received it as a gift or got it through a plant exchange. You can easily isolate new plants by putting them in a room separate from your other plants. Or at least far away from them in the same room. I put them in clear plastic bags, one plant per bag. You get to choose your method of quarantine.

I love the word quarantine: it means 40 days. And 40 days is just about right. If your new plant has hidden mealybugs or scale insects, they’ll have come out of hiding after 40 days and will be visible if you know what to look for (white cottony growths in the case of mealybugs, bumps on the stems and leaves and sticky foliage in the case of scale insects). And if you do see any, may I suggest the best thing to do is to simply to discard the plant.

I know you won’t follow my advice (if anyone had told me 30 years ago the best treatment was to toss a plant, I would have disregarded it too), so if you insist on keeping an infested plant, please at least keep it in isolation and treat it again and again until you no longer see the pest. Personally, I would require of a plant previously known to be infested with mealybugs or scale to show a full year of negative inspections before letting it loose among my other houseplants. But today I simply can’t imagine any plant that would be worth the effort.

That Was Then…

I just got back yesterday from a houseplant exchange organized by a online houseplant group. There were beautiful plants and cuttings, great conversations, wonderful exchanges of information, doughnuts, and much, much more: it was certainly well worth attending. And all the plants I brought back are now in individual transparent bags, the cuttings after I potted them up. Not one will be allowed free access to my home until it has proven itself free of bugs.

My collection is now increasing again… but I still occasionally find, inside my quarantine bags, plants with insect problems. Maybe it’s just a case of bad luck, but every orchid I’ve bought lately has turned out to be infested with mealybugs, so if orchids are your thing, be especially careful.

I learned at my expense that you don’t trifle with mealybugs or scale insects. I hope the lesson from my sad story will save you years of wasted efforts.

17 comments on “The 30 Year Mealybug Infestation: a Horror Story

  1. Good advice. Years ago I had an outbreak and used Malathion (went in guns blazing) yet they came back. I ended up throwing out a lot of plants. Yet stupid me bought a stromanthe triostar a week ago, with a very light infestation. It’s been treated thoroughly but is in quarantine and will stay there for 40 days and not one less. Sound advice. Thank you.

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  6. I’ve been battling mealybugs for a year and was quite surprised one day when look upwards and lo and behold the row of 20 foot Podocarpus trees that are on the edge of my neighbor’s yard are covered in mealy bugs. NIGHTMARE!

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  9. Thank you so much for your advice! I bought 2 orchids from the same grower that were wrapped separately though shipped in the same package. Upon arrival I quarantined them together in a room separate from my other orchids. After about 3 week I noticed scale insect on one of the plants so put it in yet another room. Though the grower gave me a refund on the plant, I decided to treat it for scale in hopes of rescuing it. I’ve been working at it diligently for over a year and have not seen one scale insect on the plant for almost 2 months. The plant that was originally shipped with it has never shown signs of scale. After reading your advice though, I will err on the side of caution and wait yet another couple months before putting the once-infested plant with the other orchids. If ever one bug on that plant shows up, the plant will regrettably be trashed. I never considered before to quarantine plants bought from the same grower at the same time. If this situation ever happens again, I’m not going to take the chance to try to rescue a plant with scale or mealy bug. You probably saved me from a feature heart-breaking infestation when acquiring new plants.

  10. Gala Christen

    Well, doesn’t your plant need air, carbon dioxide? How often do you open it, or do you leave a hole in the top? And where can I find these bags which will stand up and away from the leaves as in your picture?

    • No, the plant doesn’t need extra air: it recycles air and can live for months, even years, inside a sealed plastic bag. It doesn’t much matter if the leaves touch the bag, but you could always insert bamboo stakes to hold the bag away from the plant.

      • Gala Christen

        Really! That’s interesting. Thank you. Another question, are there any houseplants that are immune to scale and/or mealy bugs?

      • Hmm! I used to think begonias were… until I found scale on one of mine! Certainly I’ve never seen mealybugs on a begonia, but that may be a coincidence. Still, I just tried googling plants resistant to mealybugs and came up with no suggestions. I think they’re pretty much ubiquitous.

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