On Indoor Pests and Pesticides: A Chris Satch Original WIP

So, you’ve gotten your first plant, or maybe you’ve amassed a small collection, and you begin to think – what happens if bugs get into my plants?  Well, fear-not!  I’ll take you through my common-sense approach to pests, pesticides, and how to keep your indoor plants to be pest-free!

What the heck is IPM?!

IPM, or Integrated Pest Management is a method of insect/pest control that is commonly implemented in outdoor gardens.  The alternative to IPM is Eradication.  Indoors, it is very possible to completely eradicate pests, given that your home is (for all intents and purposes) a closed-system.  Outdoors, that’s not the case, and so we use IPM to manage or live with pests in populations that lead to acceptable plant damage.

So, I need to get rid of pests in my plants…

Anyway, pests just kind of happen, but they are super easy to prevent (even though you can never ever truly prevent bugs… because they’re bugs…), if you are diligent about when your windows are open, when your plants come inside, and when you assimilate new plants into your collection.

So, how do I keep my plants pest-free?  Follow these golden rules, and plant care will get a lot easier

  1. Never bring in a new plant or a plant from the outside without treating it at LEAST twice for insects.
    • Bugs are everywhere, and all plant shops have SOME baseline of pests that you WILL bring home with you.  Just accept that.
    • Quarantine all plants brought in, in another room in the house, even if the light is not ideal – this situation is temporary
    • Spray, really drench the leaves and all aboveground parts of the plant with insecticide (more on insecticides below).  Think like a bug – bugs hide in every nook and cranny, so GO OVERZEALOUS with spraying the top, bottom, sideways, well, you get the point.
    • This one is the most important… REPEAT the treatment at least once or until you no longer see signs of pests.
  2. Use the right pesticide for the right pest!
    • People who think systemic pesticides are a cure-all will be doomed to be plagued with mites for 1,000 years!!!  Systemics don’t work on all pests.
    • Broad-action insecticides like insecticidal soaps or horticultural oil (petrolium-based) are fabulous and do not risk resistance (more on these below)
  3. REPEAT the treatment until pests are gone.
    • If you just got a new plant, and it looks like there are no pests, just spray twice as a precautionary.

One more thing before we dive in:  The label of whatever you choose to use is your gospel.  Do not deviate from those instructions unless a professional (see “has a horticulture or chemistry degree” and not a youtube channel) instructs you to.  Again, this is a matter of safety, which I take very seriously.  Of course, consult the safety information (SDS, or if you’re old like me, MSDS) of whichever product you are using as gospel.

This is for the folks who never read the instructions

Problems that are not insect problems can be mitigated through cultural care; more on this in another article.  But while we are on the topic, it’s best to thin-out bushy plants if there is an infestation.  For really bad infestations, it may be best to prune off the most infested parts.

Types of common indoor pests

<<More on this later… Just wanted to get this info out there!>>

Types of insecticides and efficacy (by active ingredient)

Now, I’ll start off with this – DO NOT be afraid of the word “chemical”, and do not be afraid of things you don’t quite understand.  By definition, water is a chemical.  It’s just a word for substances that we use.  Chamicals can be dangerous, and they can be safe, depending on the substance itself, as well as the application method and concentration.  A glass of water is safe to drink, but I’ll probably drown if I had to drink an entire lake… anyway, “safety” is relative, and there are always risks with anything and everything we do (even doing nothing can be risky!).

What is an active ingredient?  It’s the actual thing that’s doing the work.  There are other helpful chemicals that increase the potency of any active ingredient in any pesticide, but you always want to choose the correct active ingredient for your pest.  Also, best practice is to use ONE dedicated spray bottle for each insecticide, and label it as such.  Do not use that spray bottle for any other chemical or insecticide.

I’ll list these in order of relative toxicity from least to most.

Neem Oil

Probably the hokiest insecticide I’ve ever seen hit the market, it’s nearly useless.  Often touted as a “completely safe” pesticide, I’ve got a newsflash for you – if it’s safe for you… it’s safe for the bug too… so you’re treating insects with… non-toxic stuff.  The only way that Neem Oil even remotely works is by the action of the physical properties of the oil itself.  Insects breathe[1] through pores in their exoskeleton.  Just like my face breaks out when my skin pores clog, the insect can’t breathe when the oil clogs those pores.  And that’s only if you completely douse the insect; direct contact.  Oh, and it smells to high heaven.

Short answer: don’t use neem oil.

IGRs – Insect Growth Regulators

There are a few of these that are food-grade-safe.  Now, just to be clear, they only arrest the insect lifestyle.  That means that whatever juveniles are there will never mature, so they can’t reproduce, but they aren’t being killed… Mixing this as an additive to something else (check if the chemistry is compatible) or using it as a preventative is my recommendation.

Horticulture Oil

My (The Plant Doctor’s) choice pesticide, as it clogs the insect’s pores while lingering as a residual, not having a smell, and is mildly toxic, as it’s a petroleum product.  It’s still relatively safe for humans to use, and gets the job done.  I’ve gotten some on me, and thus far, nothing has happened to me.  Of course, consult the safety information (SDS, or if you’re old like me, MSDS) of whichever product you are using as gospel.

Short Answer: broad-killing power, not that toxic to humans

Insecticidal soaps

Usually the “potassium salt of fatty acids”[2] is the active ingredient.  Ideally mix these in soft water, as they will be inactivated in hard water.  The calcium salts will compete with the potassium salts, and will precipitate the fats, creating actual hard soap.  Also, never spray this in combination with a treatment of hort oil, as the soap will emulsify the oil and not be as effective against the insect.

Wettable sulfur

Moreso an outdoor pesticide, this one is “organic”[3]!  Be careful as this can acidify your soil or burn your plant if you use too much or too frequently.  Very effective against mites and has the bonus of being a fungicide.  Sulfur is a powerful element that even is a nutrient to a plant, so this will even help your plants be stronger in their own immunity to fungi.

Short Answer: Useful against fungi AND mites, and nothing else.  Beware burns and pH.

Spinosad-based

Great for spider mites and thrips, as well as most other pests.  Toxic, so don’t get it on you, but not the end of the world if you do.  Wash, wash, wash, and follow the safety instructions on the label.  This should be used after the lesser-effective options have been exhausted, or if thrips are present.

Cumulus compostus

As a rule, if a plant becomes more than 50% infested, and it cost less than $50, then throw it into the compost pile.  It’s not worth saving.  I feel like people are too concerned with others feelings to give this piece of advice.  But keeping an obviously dying plant is like saving a bad relationship.  They can’t be saved.  Just.  Toss.  It.

A special note on systemic pesticides

No, systemics are not a magic insect-repelling bullet.  In fact, they’re not even supposed to be used indoors, and they don’t even work on all insects.  Mites and SOME thrips feast on the cellular guts and not the vascular fluid.  Systemics only permeate through the vascular fluids, so you can see, the insects aren’t going to be affected.  For use in greenhouses or outdoors only.

Other Notes

Hopefully this sheds some light on pesticides for your houseplants, and what to use.


References and Footnotes

[1] A pet peeve of mine when this is misspelled

[2] Cranshaw, W.S. (2008). “Insect Control: Soaps and Detergents: Fact Sheet”Colorado State University: Extension. Retrieved 4 December2019.

[3] I always laugh whenever I see the word organic because inorganic pesticides and such are considered approved for organic use… two different definitions of organic…

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