The first and most important thing to know is that pests are a part of plant parenthood. Pests are ubiquitous. If your goal is to never have any pests on your plants, you are setting unrealistic expectations. If you learn to accept that you will have to deal with them now and again, you may find you enjoy being a plant parent even more. The key is to prevent pest infestations as much as possible. Realize, too, that there’s more than just the tiny visible pests. Pests leave larvae and eggs all over your plant that you can’t even see. I know it sounds gross, but it’s true and important to know! Inspect for pests regularly. They like to hide on the undersides of leaves and stems, as well as in crevices between leaves. I recommend inspecting whenever you water your plants. In all honesty though, despite the fact that I recommend this I don’t always heed my own advice. Life - kids, job, etc get in the way so I do come upon the occasional pest infestation.
I set out to write my second blog post about pest control after many people inquired what was in a spray bottle in one of my IG photos. It was 70% rubbing alcohol, straight up. I decided it was time to revisit how I manage pests. But the truth is, I’m constantly experimenting with different methods. I’m a scientist at heart, so when I sat down to write, I went deeper and deeper into the science behind pesticides and “natural” pest control.
I keep a spray bottle of rubbing alcohol handy in case I spy any visible pests.
There are so many options out there. I walked into a local Armstrong’s nursery and found an entire aisle full of pest control products. Sometimes it was difficult to find what the actual ingredients were. That’s when I decided to research some of the more common active ingredients that are used specifically for houseplant pest control, including ones I don’t use myself. If you want to skip the sciency stuff, you can scroll towards the end to “My Pest Control Routine.”
First, a little lingo. I think it’s helpful to understand the term “systemic.” Systemic pesticides are taken up by the entire plant. Sometimes they also kill pests on contact, but they have a much longer lasting effect because the chemicals taken up by the plant root system travel up via xylem tissue. So when a pest starts sucking the juice from the plant, that juice will have the chemical in it and will kill the pest. Systemics can be synthetic or natural, organic or inorganic. In general, systemics work best in terms of controlling pests. But some of them also pose higher risks, which I’ll get into below. Then there are “contact” pesticides, which kill on contact. Some of these have little to no residual effect, while others have some lasting effect because they degrade slower. Those are still not considered systemic, because they are not taken up by the plant root system. The speed at which degradation occurs depends on environmental factors like sunlight and temperature. Many pest control agents degrade much faster when exposed to light.
Bonide brand Systemic Houseplant Insect Control contains granules that you mix in to the soil. The primary ingredient is Imidacloprid, a systemic synthetic pesticide. You can see it listed under “Active Ingredient.”
Speaking of organic, it’s important to know that organic does not necessarily mean risk-free. Let’s touch on some of the risks of pesticide use. Put into context, most of the data on risk relates to the use of pesticides in the agricultural industry, not those we use in our homes. For example, Imidacloprid, the primary ingredient in Systemic Granules (see photo) has been banned for outdoor use in the EU due to the risks it poses to the honeybee population. We are not likely to contribute to that risk when using it indoors. HOWEVER, many of us rotate our plants outside. It’s important to know that if you use the granules, you shouldn’t put your plants outside due to the risk it poses for beneficial insects. Additionally, it poses risks to aquatic invertebrates from water run-off in the agricultural industry. As the chemical degrades over time (about 8 weeks), we are not likely to contribute to that risk when it is used in the home unless we take your plants outside to water them. Regardless, it’s important to use with caution.
Many organic pesticides can also kill bees. The difference is that most are not systemics. They kill on contact then degrade fast. So if they are applied outside late in the day, they are unlikely to have much of an effect on beneficial insects.
Let’s go through some of the main chemicals, both natural and synthetic, that are used for houseplant pest control. This list is not all-inclusive, but I did try to include most of the more common ones.
Systemics
Imidacloprid, as mentioned above.
This is a neonicotinoid. It is a synthetic chemical made to mimic the properties of nicotine. A neurotoxin, it kills pests by interfering with their neurologic systems. It kills on contact and also through digestive tracts. The effect is much more potent in insects than mammals due to the strength of the chemical bond in insect nervous systems. Comes in spray on and granule forms.
This systemic pesticide works fairly well, but as above has significant risks when used outdoors as it can kill and interfere with the life cycle of many beneficial insects, including honeybees.
The amount needed to harm humans and animals is very high, but still would not use if plants are accessible to pets or toddlers. It is not likely to kill them, but can cause symptoms like vomiting and headaches if ingested.
Other neonicotinoids include clothianidin, thiamethoxam, and acetamiprid.
There are many other synthetic systemics out there, but the majority are not used on houseplants/indoors so I am not getting in to them here.
Garlic. Yes, garlic! This was a surprising one I found while researching. Garlic is a natural pest control agent that can be taken up by the plant root system when put in the growing medium. I found this old patent application online. Their application has lots of information about garlic. It works as a repellent. It can be sprayed on plants but then is more of a contact agent than a systemic and has to be reapplied regularly. It needs to have access to the root system of the plant to work as a systemic. The extract has been shown to be harmful to bee larvae. I personally don’t want my home smelling like garlic but I thought this was a fun one to throw in.
Contact Agents Labeled for Insecticidal Use
These kill on contact but do not get taken up by the plant root system. Some do have some residual effect lasting days to a week or two. However some degrade very fast, within minutes to hours.
Neem Oil
Neem oil is from the neem tree. It comes in 2 forms. Most marketed neem oil is actually a hydrophobic extract. It suffocates pests on contact and has a mild residual effect. Pure neem oil also contains Azadirachtin, which interferes with pest reproduction. It can last up to a few weeks from application. Consider it more potent and longer lasting than the hydrophobic extract. Caution when applying, as it can burn the leaves especially if they are exposed to direct sun after application. (Think of tanning oil for humans. Not healthy for us, not healthy for them :)). It can also suffocate the plant itself, especially when used in excess, by interfering with stomata respiration. Human inhalation can cause headaches and airway irritation. Many people like to wipe down their leaves with neem oil on a regular basis. I’m a bit lazier; when I use it, I use the spray form.
This is hydrophobic extract of neem oil, ready to use out of the bottle. It also comes in concentrated forms that need to be diluted down. I use this regularly for thrips and spider mites.
Spinosad
Spinosad is made by fermentation of a natural soil bacterium. It kills pests by damaging their nervous systems (neurotoxin). It breaks down rapidly in sunlight. It can kill bees if sprayed directly on them, but since it breaks down fast it doesn’t have residual effects.
Pyrethrum/pyrethrins
This is a chemical derived from dried chrysanthemum flowers. It causes nervous system damage to pests and has some residual effect (half-life is 12 days). It can kill bees and is toxic to cats.
Pyrethroids
These are synthetic pyrethrins. They are chemically modified to increase stability in sunlight. Because of this, they are more potent and the residual effects can last up to 4 weeks. There are many pyrethroids out there (over 1,000!) with many different names. Permethrin is one of the most common. Fun fact: permethrin is used topically in humans to treat scabies.
The active ingredient in this pesticide is permethrin, a synthetic pyrethrin (pyrethroid). It has been chemically modified to be more stable when exposed to light, so the effects are longer lasting. Permethrin is actually used topically in humans to treat scabies and other mite skin infections.
Insecticidal soap/Potassium salts of fatty acids (soap salts)
These cause death to pests on contact by dehydrating them. They have a very short half-life without much residual effect. I’ve found one of the best uses of these is to use them preventively. Spraying all of your plants down once a month can help keep your overall pest population under better control. For a pest infestation, they are not going to work as well as some of the options with residual effects or systemics. They are toxic to aquatic invertebrates.
Insecticidal soap contains potassium salts of fatty acids. They kill on contact without much lasting effect.
Diatomaceous Earth (DE)
This is a really interesting one. DE is a soft sedimentary rock that contains fossilized phytoplankton. It is particularly sharp to tiny pests. It lacerates/cuts their exoskeleton and dehydrates them. Because it contains silica, it’s important not to inhale it. It’s also important to get food grade as opposed to filter grade DE. Filter grade is even finer and riskier to use. DE can be used to control multiple kinds of pests, not just the usual plant pests. It can even help control fungus gnats! It can be used in solid form by sprinkling it on top of the soil, and spray form by making a slurry. Though it won’t work when wet, the lethal properties come back as soon as it dries out.
“Natural” Methods, Not Labeled for
Insecticidal Use
These methods have been passed down generations as alternatives to industry pesticides. As you’ll see, they’re not always better or safer.
Castile soap
Can work similarly to insecticidal soap, dehydrating pests. The peppermint version can also work as a repellant: aphids don’t like the smell. However, please read this article from the University of Florida regarding Castile and dish soap. It was eye opening for me especially as it came from a very trusted source. My takeaway was that it is probably safer to use soap that is labeled and intended for insecticidal use. I have also found that Castile soap tends to leave a residue on my plants. However if you choose to use it as many do, know that exact proportions are not necessary and range from 1 tbsp/quart to 1-5/gallon. Many people spray their plants regularly with this and claim good results.
Dish soap/detergent
After reading the article referenced above, I would not recommend using dish soap for pest control.
Alcohol - 70% rubbing
Alcohol kills on contact and evaporates fast. It’s one of my favorite go-tos to quickly kill any visible pests I see. I keep a spray bottle of it handy at all times. Some plants will not appreciate the harshness of 70% alcohol. Always test on a small area if you’re not sure. I have found that most hardy plants are fine with it, though. By hardy I mean thicker-leaved. You can also use a diluted form of it, approx 1-2 cups/quart of water. Some people like to mix some rubbing alcohol with insecticidal soap for their monthly prevention applications.
Pepper
Many types of peppers work as repellants. They also damage the membrane and nervous system of some pests. These include black, chili, and capsaicin to name a few. More here.
Essential oils
The smells of essential oils repel some pests. They can also disrupt the nervous system of some pests on contact. If the concentration of oil is too high though, it can damage the plant by suffocating it. Sample a small area if you decide to try this.
Biocontrol Predators
I saved perhaps the best for last. You may know that plant pests have many natural predators including ladybugs. Many gardeners (including me) release ladybugs regularly to help keep their pest population down. There are some who also use predators for their houseplants. Lacewings are one of the most common. There are many others. I haven’t tried this yet as I haven’t convinced my family of how cool it would be. Maybe someday when we’re about to leave for vacation, I’ll release some lacewings.
Shopping for Pest Control
Next time you’re shopping for pest control products, look for the “active ingredients.” If you don’t recognize them, google. More than likely if it’s not specifically listed above, it’s a neonicotinoid or a pyrethroid.
Some products contain multiple types of pesticides. For example, End All contains potassium salts of fatty acids (insecticidal soap), hydrophobic neem oil, and pyrethrin. These are all natural (not synthetic), contact control agents. You will dehydrate, suffocate, and damage the nervous system of plant pests all in one. Because of the pyrethrin, it will have some residual effect.
My Pest Control Routine
Here’s the pest control agents I’ve tried myself: Imidacloprid, insecticidal soap, castile soap, neem, pyrethrin, and alcohol.
Here’s the ones I’m planning to use moving forward, after this research: insecticidal soap, neem, DE, alcohol, possibly pyrethrin/End All.
As mentioned in the beginning, I’ve experimented quite a bit. I have been using systemic granules (Imidacloprid) mixed with the soil for some of my houseplants, sometimes just as a preventive. I don’t use them on plants that I rotate outside. After all of my reading, though, I’m going to plan to stop using them after I use up the bottles I have left. I’d rather have those granules degrade in houseplant soil than in a landfill. I will say, they tend to work fairly well so I will miss them. I just generally feel the world could use less potentially harmful chemicals.
General care and prevention: Lately I’ve been using concentrated insecticidal soap diluted down in a pressurized spray bottle, sometimes adding rubbing alcohol to the mix. I’m trying to use this on a more regular basis. The goal is to take the plants outside monthly for a good shower. A forceful shower is a great way to remove mild pests! Then a good soap application, drenching the leaves and stems with the diluted solution. Again this is best done late in the day, when pollinators are not active. I can’t say I always meet my goal of doing this monthly to every plant though. Just keeping it real!
Thrips and spider mites: I find hydrophobic neem oil works well for thrips and spider mites. First I give the plant a good shower with the hose, then I spray with neem. Spraying down weekly for a few weeks tends to hit all the life cycles of the pests. I’ve found they’re not quite as hard to get rid of as some other pests, as long as they aren’t discovered too late.
I use a pressurized spray bottle to apply insecticidal soap. Follow the directions on the bottle to dilute the soap. The goal is to cover the plant so the fluid is dripping off of it. You can add some rubbing alcohol in to the mix for a little extra kick.
Scale must be scraped off manually. I do this with my fingernail or a q-tip. Then hose down the plant, then spray down with soap or neem. Repeat weekly for 3-4 weeks. Mealybugs, which are actually a form of scale, don’t hold on as tightly but still don’t usually come off from the pressure of a hose. I use 70% rubbing alcohol regularly by spraying directly on visible mealies. This can work quite well for mild infections. I use a q-tip dipped in alcohol for some of the more difficult to access crevices. I keep a spray bottle handy at all times, though I have to say rubbing alcohol has been harder to come by in COVID times (think homemade hand sanitizer). After killing with alcohol, I remove with a q-tip. If it’s a bad infection I will then hose the plant down and treat with soap. Again needs to be done weekly for 3-4 weeks.
What the future holds for me: Next up, I plan to replace the systemic granules (Imidacloprid) with Diatomaceous Earth as a new preventive. After all of my reading it seems very promising in terms of the benefit/risk ratio. Even though it’s not a systemic, it does have lasting effects because of its innate physical properties. An additional bonus is that it can help control fungus gnats. (Note: fungus gnats are not harmful to plants, they’re just annoying!). I’ll be cautious not to inhale it :). And I’ll be sure to keep you posted with results!
Some Final Tips
If you have a severely infested plant, you might consider tossing it in your green waste bin. It may not be worth the time and effort it could take to get the infection under control, nor the risk to your other plants. If you’re not ready to toss it, consider completely unpotting it and thoroughly/forcefully rinsing the roots off before repotting. This will help get rid of some of the eggs hiding in the soil. Don’t be shy, roots are resilient! They can handle some water pressure. You can also consider giving the bare-rooted plant a bath in diluted insecticidal soap before potting back up. Going soil-free may help reduce your pest population as well. If all else fails, you may be able to save a small cutting of an infected plant. I recommend rooting the cutting in water if possible, as it will be easier to see and get rid of pests. Wait until you’ve had no visible pests for a few weeks and you have some new roots growing in before potting up. I’ve successfully done this several times.
I hope this post has inspired some of you to learn more about how we approach pest control with our plants. I encourage everyone to know a bit more about the products you’re using. Knowing the benefits and risks of pest control agents can only make us all better plant parents.