Scale has kind of been the bane of my existence. It came in on an aloe plant, and was a total bear to battle. We don’t have any outdoor space here, so all of my plants are somewhat in proximity to one another. As you can probably guess, this makes controlling pests a bit of a challenge.
Lately, I feel like the worst plant parent ever. See, my S.O. and I got this little Norfolk pine as a live Yule tree about two years ago. I love it, like I do all of my plants, and try my best to keep it healthy.
Unfortunately, up until recently, “my best” did not include “knowing what pests it’s susceptible to.” It’s got spikes all over, it has really aromatic sap, it never goes outside… what could possibly want to eat it?
As it turns out, in addition to being spiky and smelling piney, it is also irresistibly delicious to scale insects. I’m not going to lie, I cried a little when I found out. I felt like I failed as a caretaker.
Notice the dust and cat hair? As scale insects feed, they excrete a very sticky, sugary substance called “honeydew.” This can end up attracting other pests, encouraging mold growth, and, if the plant’s indoors, catching a ton of dust.
What are scale insects?
Scale insects are tormentors sent directly from Satan’s fiery butthole.
… Okay, but for real, they’re awful. They’re insects that latch onto plants and pretty much suck them dry. They’re also flattish, usually brown or beige, and the adults don’t move at all, so they blend in very well with their environment. It’s really easy to mistake them for plant tissue, especially if there aren’t many. Trouble is, their populations can grow pretty fast.
To give you an idea of how small and unobtrusive scale can be, even when there’s a ton of them.
Outdoors, scale insects aren’t usually a huge problem. Sure, they move in, but a healthy plant and a thriving population of predatory insects and birds will keep them from causing serious damage. So, in the wild (or the “wilds” of a garden, at least) they’re much more of an easily ignored nuisance than an actual problem.
For indoor plants, it’s more of an issue. Being otherwise healthy isn’t always enough for a potted plant to keep scale at bay, most homes don’t keep predatory lacewings or ladybugs as pets, and natural Bti pest control only works on bugs that are both in soil and susceptible to Bti bacterial toxins.
So, what do you do when one of your plants turns into a scale bug buffet?
To me, part of being a good steward is doing things that don’t have a negative ripple effect. For this reason, I try my hardest to avoid systemic pesticides, or any pesticides that could potentially harm anything other than the pests I’m trying to target. In a perfect world, I could just relocate unwanted bugs instead of killing them. That’s not this world, though, and I have more of a responsibility toward the plants I’ve taken into my care than I do to the pests attacking them. That’s why, when these critters rear their (nonexistent. Seriously, they are so flat) heads, I:
1. Prune, prune, prune.
A lot of plant tissue that’s been seriously damaged by scale won’t recover. If the bugs have heavily infested a certain branch or leaf, or have dried things out too much, it’s best to just cut it. Pruning away the areas where scale insects have latched on the most will immediately and drastically lower their numbers, making it easier for other measures to work.
Once you’ve identified and removed affected limbs, leaves, and other plant parts, then it’s time to start stage 2.
2. Rub them with alcohol.
Scale insects, like mealybugs, are protected by a waterproof waxy coating. This doesn’t just keep water out, it keeps moisture in. One way to get rid of scale insects is to disrupt this natural coating, which causes them to dehydrate.
Rubbing alcohol is a fast, cheap way to do this. Unfortunately, it can also harm plant tissue, so it has to be applied individually by hand. Fill a jar with alcohol, grab some cotton swabs, and start hunting the bugs down. When you see one, dip the swab in the alcohol, and give it a rub. Most times, the scale insect will come right off. Those that remain will dry out and die.
3. Soap them up.
Soap is another way to tackle the young, mobile stage of scale. It doesn’t take much, either — a few tablespoons in a gallon of water will do the trick.
As with rubbing alcohol, this has to come into contact with the scale to be effective, and will most likely need a couple of reapplications. Too much soap can also harm sensitive plants, so it’s best to start will a relatively low concentration and test it on a small area before going whole-hog.
To start with, I mix:
- 2.5 T Castile soap
- 1 gal water
- 2 T cooking oil (usually grapeseed) — optional
If that doesn’t seem to harm the plant, I might go up to:
- 5 T Castile soap
- 1 gal water
- 2 T cooking oil — optional
Once it’s mixed up, add it to a sprayer or spray bottle and thoroughly spray any areas showing signs of scale. This soap solution also has to come into contact with the insects in order to kill them, so be as thorough as you can without harming your plants. The cooking oil helps smother the bugs, but can easily be left out.
Using actual soap is important here — detergents and some surfactants aren’t great for plants, and their potential for harm may outweigh their scale-killing benefits. I like to use Dr. Bronner’s soap for this, because it’s inexpensive and readily available everywhere from the fancy organic market to the Giant down the block. If that doesn’t work for you, try your regular dish liquid, just test it on a small area to make sure your plants won’t be damaged.
As with anything else of this nature, use the lowest effective concentration of soap. If 2.5 tablespoons seems to be working alright for you, 5 tablespoons won’t necessarily be any more effective.
4. Dust them.
Diatomaceous earth is amazing stuff. I dust it under all of my appliances because, while my particular domicile doesn’t have an ongoing bug problem, we invariably get one or two trying to take refuge when pest control shows up to treat the basement or one of the other units. Such is apartment life.
Diatomaceous earth looks like a white powder. On a microscopic level, though, it is actually made up of needle-sharp splinters of the shells of tiny creatures called diatoms. These splinters are so tiny that they’re incapable of piercing skin, so diatomaceous earth is safe around people and pets. (Just don’t inhale it!) However, while they can’t injure us, they wreak absolute havoc on insects. The tiny splinters pierce and abrade their shells, which causes them to dehydrate.
To use diatomaceous earth, either dust plants with an applicator (the dust is very fine and so tends to clump together a bit, using an applicator gives a nice, light, even coating) after watering, or mix into a solution like the soap mixture given above. Shake it vigorously as you work, because the powder will settle pretty quickly.
As a warning, diatomaceous earth is not selective. Think of it like microscopic barbed wire — it’s going to injure anything that tries to cross it, not just the things you want it to get. So, if your plants spend time outdoors, drape them with a sheet while you’re letting the powder take effect. This will protect bees, ladybugs, lacewings, and other beneficial insects from injury.
Scale insects are an enormous pain. They can hide in tiny spaces and suck your plants dry, and getting rid of them involves vigilance and thoroughness. With these measures, you should be able to control scale on your plants without having to resort to pesticides.
Oh, and… Don’t do what I did. Read up on what pests your plants are susceptible to!