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Last updated: 4/14/2024
As your plant collection grows and you add more and more rare plants, a certain type of paranoia starts to creep in. It doesn’t matter who you are, you will develop The Fear.
Is that yellow spot from spidermites?!
If you’ve never had them, the paranoia is even stronger because you’re not quite sure what to look for. Is the yellowing on the edges from mites? Is that webbing from spidermites, or a cobweb?!
Here’s a rough guide on spotting the little devils, as well as how to treat them.
Meet Your (probable) Enemy: The Two Spotted Spidermite
That is a two spotted spider mite under a microscope, photo taken by yours truly when I discovered some on a grocery store calathea.
They are the ABSOLUTE. WORST.
They’re basically a tick, super tiny and just barely visible to the naked eye if you have good eyesight. If you don’t, a jeweler’s loupe should be in your plant toolkit arsenal to help with identifying pests like this one. They were originally described as a european pest, but are found all over the US, where our homes and greenhouses protect them from the cold weather that would normally kill them off.
Super-gross-not-actually-fun-fact: the two spots that give these mites their name are from poop accumulating. Newly molted spider mites often lack the spots.
Their lifecycle is short – a matter of days from egg to larvae, and full adulthood can be reached between 5 and 20 days. With such a fast development cycle, it’s easy to see how they can go from nearly nonexistent to all over everything in less than a week, particularly as females lay hundreds of eggs during their 2 to 4 week lifecycle.
They strongly prefer warm, dry conditions, so they’re most often an issue outdoors during summer and fall. Don’t worry, though, the cold doesn’t always kill them off: females can hibernate in ground litter or under bark! So they’ll just keep. coming. back.
The humidity of greenhouse growing for tropical plants tends to be less enticing for them, but they’re about as resilient as roaches, so they don’t really care if conditions aren’t perfect. They’re driven by one thing: eat, breed, and repeat. Your home is unlikely to actually be a level of humid and moist that genuinely deters them, and unless you’ve got your plants in a greenhouse outdoors that you’re able to hose down regularly…your indoor greenhouse, while humid, will be sheltered and protected enough that they can get cozy.
awesome.
Video of a spider mite we took with a basic USB-connected microscope. You can see all the molted skins, the poops, and even a few eggs (the small yellow spheres occasionally visible).
Okay, so that’s a spider mite. How do I know when there’s any on my plants?!
This is where keeping an eye out for spider mites and doing the thing you like to do are one and the same: stare at your plants every day.
Since you got your plants to enjoy them, I assume, spending a few minutes staring at them every day should be an enjoyable task. Check the leaves, stems, and in particular, any leaves with texture. My experience with spider mites has been almost entirely that they attack the soft, fleshy leaves of my tomato plants, tropical indoor plants, or my Bodhi trees (Ficus religiosa). I’ve seen people reporting or posting photos of spider mite webbing on succulents as well, although they seem far less common on cacti. I assume this is because the air flow, low water, and exposure to sunlight tends to repel the mites; when researching cactus care, it seems if they get mites at all, it’s a different species.
You’ll most often see spider mites at the base of the leaves, the underside, and anywhere the leaf isn’t flat – so you’ll really see them on textured leaves, such as those on Alocasias, or those with convenient variations in leaf texture, like Anthuriums. For some reason, they seem to be particularly fond of calatheas and marantas, although I am increasingly suspicious that there’s just some bulk grower supplying stores that has an infestation they keep shipping out.
One of the first indications you’ll see, often before the webbing has reached a point that it’s clearly visible, is a distinctive type of leaf yellowing. After seeing a few plants develop it, you’ll gain an eye for it – and if you’re unsure, grab that jeweler’s loupe and check your leaves closely! To help you develop “the eye”, see the photos below of spider mites vs not spider mites.
Spidermites
Hard to spot, but this was the beginning of a severe spidermite infestation on my Dragon Scale Alocasia baginda. Some giveaways were the funky leaf shape, yellowing on the edges even though this was a new leaf, and if you look closely (you should be able to click and see the image full size), there’s a tiny bit of the “dirt” spidermites leave behind in the grooves of the veins.
On my Alocasias, I’ve come to find that spidermite damage, particularly on new leaves, seems to result in this funky cupped-leaf shape.
Not Spidermites
This is an older leaf on my larger Philodendron verrucosum, and is a good example of what overwatering / soggy roots results in. The yellowing edges and overall yellow hue that the leaf is taking on is pretty typical of philodendrons that are mad about too much water. I check both of my verrucosums daily, and have used my jeweler’s loupe on them, and it’s genuinely just that they get too much water. With rainy, cloudy weather, even being by a south facing window isn’t enough, so the oldest leaves are yellowing. I’m still working on the balance between enough water on the grow pole and their sphagnum moss top layer (for humidity) and not letting them dry out so much they droop and die off.
This is the spotting type of damage that can be the early warning sign of spidermites. This particular Alocasia frydek is who I suspect brought spidermites into my indoor collection; I didn’t have any indoors before this plant, and afterwards, 99 problems and all of them are this plant. The speckling you can easily see is the damage from the mites, and upon close inspection, tiny webbing was visible.
This Philodendron stenolobum has spent this winter riding the struggle bus, and has not terribly enjoyed going back and forth between being in the house and outside. Combine that with overwatering it a bit when the weather was too cloudy and cool, and you get this leaf. The leaf is just dying, and likely earlier than it needed to because of winter and hating life.
This calathea began having some leaf crisping and curling leaves that seemed unusual for how well it had been doing. Closer inspection found spider mite dirt and some damage; it was harder to see on the calathea than on greener-leafed plants, which may be why they’re considered spider mite bait. It’s not that they are particularly attractive to spider mites, but rather than it’s harder to see them early on.
Scroll through the red leaf anthurium above – if you look closely, you can see tiny little webbing on that brand spanking new leaf.
SPIDER MITES? IS THAT SPIDER MITES?
No.
Is spider.
This is my beloved Philodendron mamei showing the very earliest signs of spider mites. This one’s a twofer – the top corner edge is what shows spider mite damage (that tell-tale yellow fade/spotting thing), while the lower edge shows some yellowing and crisping from inconsistent watering. This leaf is one of the oldest leafs on this plant, and only the two oldest leaves were beginning to show signs of spider mites.
Jen staring at her plants all the time = 1
spider mites = I don’t want to talk about it
The saddest of sad Alocasia sinuata leaves. This isn’t spider mites – it’s watering weirdness, and the leaf managing to rest on a begonia pot with damp sphagnum, causing some rot.
Sad Alocasia is sad. They all hate winter, even in San Diego, at least for me.
Jewel Alocasias in particular hate winter, and need plenty of babying to get through while looking pretty.
These little Alocasia “Pink Dragon” leaves both had spider mite damage. You can see that they are somewhat rounder and an odd shape compared to what typical searches of this type of Alocasia would show you, and the tell-tale yellowing around the outer edges is there. Both leaves are slightly cup shaped, and mites were primarily on the bottom of the leaves on the outer edges.
That’s not spidermites, silly, that’s variegation! This is just an average, slightly dusty leaf of Golden Pothos.
This particular plant didn’t produce any variegated leaves when I first propped it from a mystery cutting box, so getting the lightly variegated leaves as it grew was a pleasant surprise. Totally healthy and fine.
Prevention is the Best Cure for Spider mites: How to Not Get Spider mites
First, let me be clear: getting spider mites does not make you a bad plant parent, or bad at plants, or a terrible grower, or anything. They are the plant equivalent of fleas. You don’t consider someone a bad pet parent if their pet gets fleas, just if they don’t take care of it, right?
And the first and easiest step of taking care of fleas is preventing them from getting on your pet in the first place.
For spider mites, the first and most basic level of prevention is to quarantine new plants. If you are forking over money for rare, hard to find, or just a plant you really like, protect the others in your home and keep the new one quarantined in a different room or area for at least a month. This helps you spot if any pests hitchhike home, and ensures that if they did, they don’t spread.
Most of us know this is probably a good idea, much like eating vegetables and walking 10,000 steps every day, but do we do this?
No.
No we do not.
So if you don’t, then the other best practice preventative measure is to routinely spray down your plants to clean the leaves. Drag them bad boys into the shower, and use the shower spray to clean the leaves, top and underside. Or use the hose, if they’re outside. If it’s too big to cart into the shower, then use a wet cloth to wipe down each and every leaf at least every month or two. This isn’t just to pamper your plants, but because the less dust and debris is on the leaves, the fewer places there are for spider mites to get cozy. Clean, healthy leaves resist pests! You’re also mechanically removing any eggs, poop, webs, or mites and then either flushing them down the drain or throwing them out on the cloth you use to wipe down leaves, so you’re removing anything before it gets to be too bad.
So, one-two punch:
One: Quarantine so your other precious plant babies don’t get the mites
Two: Keep them leafs CLEAN and SPARKLY
How to Treat Spider Mites
How do you get rid of spider mites without also throwing out your plant?! A lot of people seem to see spider mites as an immediate death sentence for whatever plant they’re on, but that’s not actually taking care of the problem. You don’t throw out your pet if they get fleas, right?
It’s also not addressing that the spider mites have probably spread in your collection and so something else is going to show them eventually.
yaaaaaaaay
So, treating them is your best course forward, especially if it’s beloved or expensive plant (you think I’m throwing out my Philodendron mamei or my Alocasia baginda?!).
Disclaimer: I don’t think there’s a natural method of treatment that is entirely effective for eliminating spider mites indoor collections, or even for outdoor collections. If you really want to eradicate your spider mites, ya’ll need CHEMICALS
Step 1: Clean Dem Leafs
You’ll be doing this religiously so get used to it. Drag the plant into the shower if you can, or get set up for wiping the leaves with water first. Rinse the leaves thoroughly, top and bottom, and be sure to go through each and every leaf on the plant. If your shower has high water pressure, be cautious about doing this, as the high water pressure can damage young, tender leaves. Using a kitchen sink sprayer or even a spray bottle may work better in those cases. Be super diligent, especially the first time, and really rinse off all the leaves and flush the soil thoroughly. You’ll want to flush the soil out thoroughly for later, when you add ChEmIcALs.
Step 2: Topical leaf treatment
You can use neem oil, but I personally find it to be super ineffective, mostly because I am lazy AF and I am not re-wiping leaves down every few days until the mite life cycle is complete. Neem oil can work (I used it for my fiddle leafs that were neighbors to the Alocasia frydek in combination with Step 3, and it worked well), but it needs to be diluted appropriately and applied thoroughly. Do not half ass your neem oil, and make sure to wipe it on the leaf petioles, under the leaves, everywhere. If you’re going to try it, you’ll need to keep reapplying when you see that the leaves aren’t shiny anymore (sometimes every few days, sometimes as long as a week to ten days). The neem oil is a general pest repellent (yay, no new pests) and will smother any spider mites that are on your leaves (yay, murder).
If you don’t want to deal with carefully and diligently wiping every single leaf with a neem oil paper towel (that’s me), you can use a topical spray. I’ve had a lot of success using the Ortho brand food-safe insecticide for aphids and other food-crop pests as my topical treatment, and I recommend it as your initial method of murdering the little pests. [2024 edit: I can’t find this exact stuff online anymore, so I’ve switch to using the BioAdvanced concentrate instead.] As with the neem oil, you’ll need to get the top and bottom of each leaf, but unlike neem oil, this stuff comes in a handy spray bottle, so you can just angle your sprays and call it good. Naturally, do this AFTER you have washed off all the leaves so that the tasty tasty poison stays on the leaf surface and smothers some spider mites. I prefer the food-crop-safe insecticide for my topical treatment as it’s safer for humans to be around and less harmful than other pesticides. Yes, if I truly wanted to avoid pesticides and chemical exposure, I’d use natural methods, but then I’d probably still have spidermites, so. Pick one.
You can also use an insecticidal soap, or even try dish soap, but honestly, they’re harder to get the ratios quite right, and getting it wrong can sometimes kill your plants. Some people might see success with soaps, but I generally find it’s not quite enough compared to a good old fashioned pesticide. Again, you’ll be repeating this, so you should be sure your method is something convenient enough that you’ll keep it up.
Step 3: Systemic treatment
I pretty firmly believe you can’t really eradicate spider mites without also using a systemic treatment, especially for larger plants or those producing lots of new or small growth. If you can’t spray the leaves directly (like begonias), you need something that the plants can eat and put into their leafy flesh that’ll kill the mites.
My favorite systemic treatment to date has been Bonide Systemic Houseplant Insect Control, both for ease of application and low cost. It’s pellets, which you mix into the soil as per the directions, and then the plant absorbs the poison and just kills anything that bites it for up to two months. The primary ingredient is the acephate, which I’ll discuss in more detail at the end of this post as to why acephate is so effective.
The catch with acephate is that it is super duper toxic to things like people, pets, and wildlife, so don’t use it for things where water runs off into the groundwater, or where your pets might chew leaves or eat dirt. Cat people, put cages around your plants or put them in a bubble or something. You also don’t want to use it when your plants are flowering, as it can kill bees, butterflies, and other beneficial pollinators – so for your indoor plants, much less of an issue than anything outside. This stuff is basically the plant “big guns” and I am all about it. You can use it safely if you follow directions, so please god, READ THE LABEL.
I use a tiny little bonsai rake to mix the bonide into the soil, and water as normal afterward. The damp soil from you thoroughly flushing the soil before this means the pellets will be absorbed/diluted into the soil that much faster, and picked up by the plant to be carreid out to the leaves for the murdering of mites.
Because it takes time for the plant to distribute poison all through its veins, a topical leaf treatment is needed in conjunction with the bonide. This prevents the mites from vacating to another plant to bide their time.
Step 4: Repeat steps 1 and 2 every week or two for at least a month
Yup, you gotta keep the leafs clean and then re-smother any new mites that have escaped being poisoned by what they eat. You’ll have to be diligent for at least a month, with regular reapplications of topical treatment after cleaning the leaves, and then you can ease up for a bit while the bonide works through the plant’s system. Bonide can last up to 8 weeks, but it’s somewhere between 4 – 8, so in your second month of treating the plants you’ll have to keep an eye on them.
Step 5: After 2 months, repeat
You don’t have to go whole-hog on the repeated leaf clean and spray route, but you do need to repeat the leaf cleaning, topical spray, and bonide soil application.
Spidermites are resilient little shits, and at least one female likely left eggs hidden somewhere. You’re repeating the treatment so that any eggs or hibernating mites wake up and hatch and then promptly eat poison or are smothered.
If you see any actual mites at this stage, you should start completely over with the obsessive leaf cleaning and spraying. You move on to the final murder stage as a clean up for any sneaky spider mites your eyes might miss. Spider mites are like roaches: for every one you can see, there’s a hundred hiding.
Other chemical treatment options:
I recently picked up some of the Bioadvanced systemic/topical combo concentrate as a preventative for mealy bugs and aphids outdoors, and plan on trying it for my final round treatment for spider mites on the Philodendron mamei [see note above; it works!]. Bayer supposedly also makes an excellent combo topical/systemic, but with both, be sure to read the directions thoroughly before use.
Zoomed out image of spidermites. All the debris and dust you see on your plants is molted spider mite skins and poop. Delightful.
“Natural Methods for Treating Spider mites
There are multiple methods of killing spider mites that rely less on poisoning them and more on good old fashioned physical murdering. Namely, predatory insects that eat spider mites.
There are numerous types of predatory mites, which are excellent for use in greenhouses or outdoor applications where a toxic systemic chemical is undesirable for what are hopefully obvious reasons. Predatory mite species include Amblyseius cucumeris (also helps with thrips), Neoseiulus californicus (also helps with citrus pests), Phytoseiulus persimilis (gobbles dem spider mites), and/or Amblyseius swirskii (also eats thrips and whiteflies). Does this sound like the special blend from Nature’s Good Guys? That’s because it is!
Predatory mites work well due to their equally rapid lifecycle, and because they won’t decimate other beneficial insects or animals or harm the local ecosystem. Before you release predatory mites (or any other natural predator), be sure you haven’t sprayed any pesticides for at least a week – including neem oil! You’ll have to let the mites run rampant for a bit, only using water to try and clean the leaves and save your plants, while you let nature balance enough for something natural to come in and save the day.
The other natural method is Lacewing larvae, or ant lions. They are super cool, kind of bitey, and in my personal experience, totally useless. They definitely like eating spider mites, and will eat plenty, but their life cycle doesn’t quite match up well enough to how spider mites tend to linger. Indoors, you just have a crap ton of angry tiny ant lions wandering around looking for food, and while you aren’t very likely to see them wandering, your partner or spouse or children usually won’t be very excited about the idea of tiny angry insects wandering around the house.
The dirty little “secret” about outdoor growing, greenhouses, and predatory mites / natural treatment
Why do predatory mites only work for a short while indoors, but a single release of predatory mites or lacewings can last an entire season or more outdoors?
When we’re panicking about the undesirable thing all over our plants, or trying to be conscientious about treatment, we can sometimes overlook something essential: predators need prey, and are little autonomous creatures.
Predatory mites and insects only work when they have prey, and they aren’t exactly thorough. They eat until they’re full, and cruise around to find more things to eat. They aren’t hunting with the single minded purpose of eradicating spider mites so your plants look pretty again; just like spider mites, predatory mites are only looking to eat, breed, and poop. They do not have an ulterior motive, and in fact, benefit by not completely eating every single mite they find (although they would, if they could find them all).
So the “dirty secret” of using predatory mites and outdoor growing with organic methods?
They will never kill and eat them all. They never go away. If you are using all-natural methods of pest control, you will never fully eradicate your spider mites, mealy bugs, scale, or whatever. You might come close, particularly indoors in controlled conditions and not bringing ANY new plants in for at least 1 – 2 months, but even that’s not guaranteed.
For full eradication of pests, you need those sweet, sweet toxins found in chemicals. Or you need a healthy balance of pests and natural pest control, which brings me to the final point and wrap up of this blog:
Does systemic pesticide use cause spider mites to reproduce MORE / FASTER?!
Short answer: nope.
Here’s the science answer:
Percolating a tiny bit around Instagram, and I assume through other social media groups, is a discussion that systemic pesticide use may actually cause spider mites to reproduce faster/in larger quantities/make the infestation worse. Sometimes studies are cited, sometimes not, but if you do see anyone claiming this, ask for a source. I for one am dying to find whichever study or paper it is that actually says that the Acephate toxin used in Bonide’s systemic houseplant insect control (my fave) is what leads to pesticide tolerance and rapid reproduction, and have yet to find a reputable source on it.
To be clear: I’m open for studies, research papers, or other peer-reviewed information that stands up to academic scrutiny – but I am not down for Instagram Ingrid posting a pretty square or talking in a YouTube video and calling that good. I want to see real science that documents why and/or how this chemical causes more problems.
Acephate should not be used as a continual, regular application to your house plants, greenhouse plants, or outdoor plants. It is toxic and can potentially throw off the ability of songbirds to navigate or tell north from south. It is a limited use, extreme measure that is acceptable in small quantities and for a limited time.
This paper notes that spraying my favorite poison, Acephate, didn’t have long lasting effects, even when combined with imidaclorprid or compared to permethrin, cypermethrin, or fenitrothion. Initial effects of spraying the poisons did have an impact on the populations of mites, thrips, and other pests, but they eventually rebounded. Lacking from the brief, which is all there is free access to, is a description of how many times the chemicals were sprayed, if the population peaks corresponded to sprays, or any other information about how the chemical sprays were applied and expected to behave. Note that the chemical is sprayed topically, not systemically, as it was used on a food crop (soy beans). The only conclusion we can reasonably draw from this paper is that spraying chemical treatments doesn’t work long term on its own…which isn’t terribly surprising when you see that the brief notes that populations declined, not disappeared. If there’s any pests left after you treat the plants with something that does not linger long term, or do not reapply (and we don’t know if either of those things happened or was expected to happen from the brief), then the pests will breed and make more. For our purposes, the paper is kind of useless, aside from reaffirming that you gotta kill ’em all.
This paper discusses other chemical treatments used on peanut plants, though not our friendly ground water poisoning Acephate, but instead mancozeb, carbaryl, and a handful of other chemicals plus combinations. The rate of natural increase was measured and compared, although it is important to note that in the brief, we can’t see how they determined this number, how they conducted the study, or the other influencing elements behind the “rate of natural increase” that was used to evaluate if the treatments impacted this rate. The paper did find that some chemicals contributed to an increased reproductive rate, while others didn’t. The article is also from 1982, so the chemicals used then, the quantities and applications may and probably are quite different than what’s available today. For our purposes, we can conclude that we shouldn’t use mancozeb, carbaryl, or the combination of the two alone if we expect to kill spidermites, as those had some impact on reproductive rates. Mancozeb is used today for blight/fungus control, but is a possible human carcinogen, so try not to use it if you can help it. This is also true of carbaryl, which is still used as a head lice treatment, and is illegal in the UK, Austria, Denmark, Sweden, Iran, Germany, and Angola. Fun.
Acaricide resistance is a concern not just for spider mites, but also tick control, and as a result it has been heavily studied. Helpfully, this paper reviews the most common chemicals that are considered acaricides, as well as which species of ticks are documented as resistant. Notably, it’s primarily synthetic pyrethroids and specific organophosphates, and acephate is not included in their list for measuring or monitoring. Our takeaway is that for ticks, we should do more research, and there’s not much we’ve learned regarding spider mites aside from potentially that ivermectrin and similar pyrethrins can and likely will result in pesticide-tolerant spider mites. This related paper reviews acaricide resistance in spider mites specifically, but again, is reviewing compounds that are not what we’re looking at: acephate.
This paper references actual outbreaks of spider mites on elm trees in urban landscapes, but is referencing Imidacloprid, not Acephate. As you read through the paper, it discusses an interesting point that is right in line with what I just pointed out about natural pest control and pests: by using the imidacloprid on the stand of elms, the forest control ended up also killing all the beneficial predatory insects as well. This led to a boom in the spider mites. The actual cause for spider mite population booms was not so much the chemical treatment, but the lack of predators. This makes logical sense and again, does not actually apply to the active chemical we’re looking at here.
Basically, acephate is fairly toxic, but highly effective, which is why it works so well on spider mites and other pests.
I recommend the Bonide pellets not because I’m invested in the stock (I’m not, but by now I should be), but because the pellet formulation makes it easy to mix into the soil (minimizing the exposure of your lungs to dust from the pesticide), and is already diluted in a dose that is easy to apply. You can apply it cautiously and safely, and when used appropriately, the quantities are low enough so as to probably not kill the environment.
Is it ideal long term? Nope. But when it comes to iradicating spider mites in indoor environments, you need to get a little gnarly. Your house cannot function like a natural ecosystem, and even small outdoor collections are not large enough to sustain populations of predatory mites in a balance that would last. As a seller shipping out plants, it’s frankly irresponsible to simply ship out plants that are “naturally” protected from spidermites without providing some treatment or pest removal before the plants are shipped. Humans shipping plants all over the world has shifted where pests live and breed, and many pests are invasive or non native. While it’s not ideal to rely heavily on chemical treatments for all pests, going purely organic or relying exclusively on introduced predators is not solid enough insurance to protect all areas and regions from potentially larger effects due to introduced pests.
Use your own best judgement, but if you’re trying to manage your own collection of valuable, rare, or treasured plants, then a little bit of (responsible) chemical warfare is warranted.
If you have scholarly articles to share regarding acephate and its benefits or harms, please send them to me at [email protected] – I am always, always happy to share data.
