Scale insects are one of the more difficult (and annoying) houseplant pests to control. Their protective shells render normal pesticide sprays less effective. Additionally, their lack of movement and drab coloration can keep their presence hidden from us until it is a large infestation.

This post will discuss what to look for to identify scale on your houseplants and what to do if you find them.

Table of Contents

How to Identify Whether You Have Scale
—- What is Scale / What does it look like?
—- What are some signs your plant has scale?

How do you get rid of scale on your houseplant?
—- What if it is a severe infestation?

How can you avoid your plants getting scale?

How to Identify Whether You have Scale?

The best way to identify whether your plant might have scale is to know what scale is, what it looks like, and what signs your plant gives you to signal you might be dealing with scale.

What is Scale / What does Scale look like?

Scale is a small, often oval/round insect that feeds on plants by sucking the sap out of their leaves and stems. These insects are often light to dark brown (though they can be nearly any other color as well) and are relatively flat.

The scale insect body has a protective coating, which looks like a waxy or hard scale, earning its name. This coating makes it a difficult pest to control because many spray-on pesticides will not penetrate this armor.

Some scale species lay eggs beneath the waxy shield where they will be protected. The eggs hatch and the young scale insects crawl out to find a feeding spot to attach, grow, and live.

When a scale is at this mobile stage, it is referred to as a crawler and is more easily managed because it lacks the protective shell.

You can find scale insects anywhere on the stems and leaves of your plant.

There are technically two families of scale insects – hard scale and soft scale, but they can be controlled in a similar fashion.

The main differences between soft and hard scale are:

—- Soft scale has a waxy shell protecting them. They also produce honeydew while feeding. They are typically oval in shape.

—- Hard scale has an armored or hard shell protecting them and do not produce honeydew while feeding. Hard scale can be found in a range of shapes from oblong to circular.

Here are some pictures of scale so you can get an idea of what to look for:

Photo by Rob Curtis, https://www.inaturalist.org/photos/523430
Photo by Jon Sullivan, https://www.inaturalist.org/photos/1198170
Photo by Alison Northup, https://www.inaturalist.org/photos/9209166

What are some signs your plant has Scale?

  1. One sign your plant has scale is the telltale round/ovular bumps on stems or leaves (often the undersides, but can be on the tops also) of your plant
  2. You may also see shiny/sticky sap that some species secrete (called honeydew)
  3. This honeydew can cause a black sooty mold or fungus to grow – the mold will not damage your plant, but looks unattractive. It will die off as the scale infestation dies off.
  4. The honeydew also attracts ants to the plant, particularly if the plant is housed outdoors. The ants are there to eat the honeydew, not the plant and will leave once the scale is gone.
  5. Scale can also cause poor growth, a sickly looking plant, and yellowing or discolored leaves

How Do You Get Rid of Scale on Your Houseplant?

  1. Remove as many as you can by hand
    • This is the easiest way to ensure the adults will be removed since sprays do not penetrate their shells
    • Adults can be picked off using a tool or fingernail.
    • You could also use a cotton swab or pad dipped in rubbing alcohol to dab and remove them, which will kill them in the process.
  2. Thoroughly wash off the plant in the sink and remove any black sooty mold if needed
  3. Spray plant with a pesticide to control the crawlers (younger scale insects that haven’t developed a protective armor/coating)
    • Homemade option #1: 4 ounces rubbing alcohol, 1.5 tsp mild dish soap, and 16 ounces water
    • Homemade option #2: 16 ounces water, .5 tsp neem oil, .75 tsp mild dish soap
    • A premade Insecticidal soap
  4. Repeat removing adult scales and spraying the plant with a pesticide weekly until the infestation is gone

What if it is a severe infestation?

Unfortunately, scale insects are one of the hardest pests to gain control over when a large infestation has broken out. If you find yourself with a large infestation and feel like the method above is not enough, you have 2 options (that I’m aware of).

  1. Systemic Pesticide
    • I almost never recommend this option because we are talking about VERY toxic chemicals that are bad for you and bad for the environment.

      If your plant lives outside, I would recommend not using it as it kills beneficial insects and can harm any other life that comes into contact with your plant. If it is indoors, this is the last resort option for me.

      Systemic pesticides work by being absorbed by the plant through its roots and pumping chemicals that are toxic to pests throughout the plant. The result is that any pests that eat the plant are killed.

      You apply systemic pesticides by mixing it into the top layer of the plant’s potting mix or diluting it in water. If you mix it into the potting mix, the plant will absorb the pesticide when you water the plant.

      Once the plant absorbs these chemicals, it becomes toxic to you, your family, and the pests you are trying to kill for the next couple of months.

      IMPORTANT NOTES ABOUT SYSTEMIC PESTICIDES:
      1. Because they are so powerful, it is very important to read the instructions and use the exact amount needed for the plant’s size as too much can kill your plant
      2. These chemicals are very dangerous to people and pets so be sure to use with caution and to keep the container and the treated plant somewhere away from small children and pets
  2. Some infestations are so out of control that it isn’t worth risking your other plants to keep a severely sick plant around and it may be time to let it go. This can be tough, but is occasionally necessary.

    If this is a choice that you find yourself needing to make, I am sorry. It really stinks to have a plant you love be too far gone to be able to recover from an infestation.

Additional information on systemic pesticides:

‘Systemic’ pesticides are taken up inside the plant, typically through the root system, so that every part of the plant then contains the chemical. (I say ‘chemical’ here because I can’t think of any organic systemics.) As you can imagine, systemics on food crops are an especially bad idea. In fact, in one of their very first uses, the string beans they were “protecting” became as poisonous to people as the attacking bean beetles.
[…]
‘Merit is the most widely used systemic pesticide’, Jay Feldman explained, ‘and the active ingredient in Merit is the chemical most implicated by researchers in the Colony Collapse Disorder decimating honeybee hives around the world. Growers use Merit to protect their plants, bees ingest the chemical when they collect pollen from those plants, and boom—the bees are poisoned because the chemical is in every part of the plant, including the pollen. And this isn’t specific to just Merit; its just one example of how these types of pesticides can have a profound and deadly impact on non-target organisms like pollinators.’

And of course, without pollinators, we got no food or flowers.

Mike, ‘Systemic’ Pesticides Poison Every Pore of Your Plants, https://www.gardensalive.com/product/systemic-pesticides-poison-every-pore-of-your-plants

How can you avoid your plants getting scale?

Scale often rides in on new plants you buy or receive as a gift. As such, it is hard to avoid.

You can avoid spreading it to your other plants, however, by quarantining the new plant.

The recommendation is to keep a new plant away from existing plants for at least 3 weeks. If the plant is pest-free after 3 weeks, you can introduce it to your established plants.

Unfortunately, this isn’t always feasible for those of us with many plants and limited space.

If you can’t quarantine your plant, here are some other possible ways to help stop the spread of pests:

Do not allow your plants to touch one another so houseplant pests, including scale, have to work harder to move from one plant to another.

You can also pretreat plants with an organic spray to hopefully control or guard against outbreaks.

I personally use the diluted neem oil and dish soap spray mentioned above as a pre-treatment on plants. This has been effective for me in MOST cases. If a plant arrives in a particularly weak state, pretreating doesn’t always help to deter pests.

I just found a plant with aphids for the third time this week and I’m positive it is because the plant has never fully recovered after each attack. I’ve been checking daily and I think the aphids are gone again. *fingers crossed*

The truth is that pests can find a way even if we quarantine, pretreat, and never let our plants touch – but they will have a more difficult time finding a way, which is what we want!

Big Takeaways:

  1. Scale insects are particularly hard to treat because of the hard or waxy shell they use to protect themselves
  2. Look for sticky sap, black mold, round-ish bumps (on leaves and stems), and discolored leaves to help identify whether you have scale on your plant
  3. To remove them, manually get rid of as many as possible and then treat the plant with an organic, pesticidal spray – then repeat this as necessary until the infestation is gone.

Click to read last week’s post: For people who want to know more about Scindapsus

Want to learn more about houseplant care? Check out these posts:

Lighting: How to Choose the Perfect Houseplant for the Lighting in Your Home!
Bright Indirect Light: Houseplant Care: What is Bright Indirect Light?
Watering: How to Water Your Houseplants Correctly Every Time
Passive Hydro: How to Propagate Houseplants Using Passive Hydro
Potting Mix: What Potting Mix Will Help Your Houseplant Grow and Thrive
Choosing a Pot: Pick the Right Pot For Your Houseplant
Exposing My Mistakes! Sharing My Biggest Houseplant Mistakes So You Can Avoid Them!
Propagation: How to Propagate a Hoya Lisa Cutting in Water
Fertilizer 101: Answers to the Most Common Questions About Fertilizer

Want to learn about botany for plant lovers? These posts are for you!

Why bother with Botanical Latin: Why You Need to Know Botanical Latin When Shopping for Houseplants
Botanical Latin 101: For People Who Want to Understand Botanical Latin
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What is Tissue Culture?: Are Tissue-Cultured Houseplants of Poor Quality?

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