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Pests & pest mitigation


If you have plants, you'll have bugs. Some bugs can be harmful (we call them pests) while others are actually beneficial. I invite you to (1) assume all plants have pests and (2) adopt a prevention and mitigation routine before an outbreak occurs. A healthy houseplant pest prevention/mitigation routine requires very little time every month compared to panic-treating an outbreak. In this blog post I'll discuss identification of common houseplant pests, as well as my preferred prevention and treatment methods.


There are many ways to prevent and treat pests. This blog is a collection of what I do and is in no way meant to be a comprehensive look at all possible prevention and treatment options. Be sure to check out my Toolbox for the products I use (or make)!

 

Assume all plants have pests

Did you just pickup a great new plant from your local plant store, hardware store plant section, or purge page seller? No matter where the plant came from, assume it has pests. There are so many different critters that are not visible to the naked eye. Bugs like to hide on the underside of leaves, on the "nooks and crannies" of petioles and stems, and in the soil or on the rim of the pot. Additionally, many common houseplant pests lay their eggs in the soil and live adults could be absent on the plant itself until the eggs hatch days or weeks after you've brought the plant home.

Quarantine & Treat

The very first thing you should do is put new plants in isolation, or "time out", away from your other plants. I like to do this in a bathtub or shower, sometimes the kitchen sink, as long as there is enough light to support the plant (moderate light is totally fine). Treat the plant for pests (all treatment info in the section below) and keep isolated for at least 3-5 days. If you picked something up on clearance or from a big-box store (looking at you $1 peace lily), try to give it more time in quarantine- countless houseplant owners find all sorts of critters on their cheap finds that spread rapidly to their other plants.


It is a Pam Common Practice to annoy her husband with quarantine plants on the kitchen counter for a couple of weeks. I tell him better safe than sorry...


Newer collections

If you are new to collecting houseplants, or are expanding at a rapid pace, keep in mind you will likely deal with more pest issues at first. When your collecting habit (ha, it's a habit! change my mind!) begins to slow down and you settle in with your current collection, you'll find your pest issues start to slow down, too. This is because you are more likely to introduce new pests each time you bring home a new plant. Fewer new plants, fewer bugs that ride along. Additionally, as you get your pest mitigation routine down, you'll feel less stressed and more in control.

 

General prevention & mitigation tips

  • Replace the soil the plant comes in. The potting medium most of store-bought plants come in is fairly inappropriate for growing plants indoors anyway-- it holds too much moisture. It is also the prime medium for pests and their eggs to tag along and make their way into my house. Plants that come from collectors I trust get to keep their soil.

  • Use a systemic insecticide in the potting medium. This is an easy prevention technique! Use systemic granules in soil every 8 weeks to prevent mealys, aphids, scale, white flies, some fungus gnats, and some thrips (not mites!). Or, use a heavy-duty systemic liquid that protects plants for up to a year! Downside: You cannot use this on anything edible, and it is not exactly safe for pets or children that decide your houseplant dirt is a tasty snack. I do not use this in my greenhouse.

  • Horticultural oil or insect-killing soap every month. Every month I put a bunch of plants in the bathtub or shower and rinse them with water and drench them thoroughly with my DIY neem soap. I let the plants sit overnight to dry, them put them back in their usual place the next morning. This technique is useful because it will suffocate/kill anything living on the plant at the time, and by doing each "zone" of plants regularly, I am mitigating potential outbreaks if there are living bugs.

  • Inspect regularly. Whenever you are checking your plants for watering needs, give 'em a glance for possible signs of pests. Since you likely won't see the pests themselves, look for sudden yellowing or browning of leaves, speckling, and other signs of bugs. By catching them early you can prevent a disaster!

  • Spot treat. Sometimes a little nest of mealy bugs will pop up on one hoya. I don't panic! I will apply rubbing alcohol using a makeup brush on the area I found the mealys (it's usually just a little fluff on a small section of vine). Or, I'll take the plant and rinse the leaves well under the sink. Catch them early and they can't spread.

 

Identifying pests

Truth is, you'll likely see damage to your plant before you'll see a pest. It can be a tough situation because signs your plant is ailing could be a number of factors: environmental conditions (poor light, irregular or over watering, humidity issues), bacterial/fungal spread, pests, physical damage (such as puppy jumping into the fiddle leaf fig to see what it feels like), and more. The more exposure you have to common houseplant ailments and pest problems, the better you'll get at identifying the problem and deciding a good course of action.


Mealy bugs

These are probably the most common houseplant pest I see on my own collection and among local houseplant enthusiasts. They are gross, but one of the easiest to take care of because they move slow and rarely fly. Hoyas are mealy magnets, it seems.



Visible mealy bugs These look like little sticky cotton-y fluff or fuzz on your plant, generally in the space between a leaf and a petiole. They hardly move, so if you poke them they just stay in place. There are also types of mealys that live in the soil itself and munch on roots. The only way to know if this is happening is if your plant is ailing and if you take the plant out of the pot to inspect.

Signs of mealy bugs Sticky residue on leaves, petioles, and stems. Leaves on the middle of the plant are turning yellow and dropping with few other reasons. Sometimes you'll see a Cryptolaemus montrouzier ("Mealy bug destroyer") on the plant before you'll see a mealy bug (they look like pale, tiny rollie pollie/pill bugs). This is because those little destroyers are actually eating the mealy bugs for you!



Mites & Spider mites

There are hundreds of types of mites! The most common houseplant mite is a spider mite. They thrive in hot and dry conditions and their eggs can be dormant for extended periods of time. It is common to see these pop up in the summer and start to disappear again in the winter (unless your house is hot and dry in the winter, too).

Visible mites You will likely never see mites on your plant leaves unless you are looking very closely, but they come in all sorts of colors (white, red, dark brown, tan) and sizes (microscopic, pen-tip size). They live on leaves and usually lay their eggs on the leaves, too. They can be very slow or very fast!


Signs of mites Spider mites leave little tiny webs all over the plant leaf and stem, which is where they lay their eggs. The webs are very fine but can sometimes be mistaken as actual spider webs.Other signs include visible "speckling" on the plant leaf itself, which is left behind when a mite has sucked fluids from the plant leaf and moved on. You can see this in my photo of this hoya megalaster that I didn't realize had a mite issue until taking a photo!


Tumid mites are a nuisance, too. They live inside the cataphyll of a plant and suck on a new leaf's resources before it has even unfurled! When the leaf eventually opens up we see pen-tip sized spots fairly evenly spaced throughout the leaf blade. It is very difficult to get rid of these, as they disappear when the leaf unfurls. They are common in many philodendron and thaumatophyllum.


Special treatment notes: Mites are not affected by systemic insecticide granules and generally require treatment every 5-7 days to keep up with the mite lifecycle until eradicated. If your treatments are not knocking them out, you may need to get a heavy-duty miticide. Keep your plants in higher humidity as additional protection against mite outbreaks.


Scale & Aphids

Both of these pests are sap-suckers like their mealy cousins. Aphids and soft-bodied scale

are very soft and easy to squish with your fingers. Armored scale, however, has a thick protective shield that keeps them protected on our plants and makes them slightly impervious to topical pesticide.


Visible aphids and scale They appear as little round lumps, sometimes fat and sometimes slender, on the surface of the plant. Aphids move much faster than scale and

you can see visible legs. Both types of pests come in every possible color. Check out the black aphids on my black lace elderberry... ants farm them every year and harvest their honeydew.


Signs of aphids and scale Oh don't worry, you'll see the pests themselves. But they leave behind a sticky honeydew like mealy bugs and will suck the life from the plant causing the cells to pale and look withered.

Thrips

If you say this word to a houseplant collector they will let out a "fuuuuuck" and get armed with a blow torch. Thrips are some of the hardest to deal with because they are fast, can fly, have quick lifecycles (and produce zillions of offspring in a very short amount of time), and spread easily from plant to plant. They scrape at leaves and flowers and they suck sap.


Visible thrips

Photo courtesy of Hahnah Gibson

Thrips look like a very small segment of thread and can come in every possible color. I have mixed feelings about being able to see thrips. For every one thrip you see, there are probably a hundred you can't see. Thrips do a great job at being present one minute and disappear the next, so when you're looking you need to try different times of the day and multiple different surfaces of the plant (undersides of the leaves is a common hiding spot as this is also where some species they lay their eggs).


Signs of thrips This is likely what you'll notice- small, irregular spots on the leaves that are surrounded by a ring of sorts. This is necrotic (dead) tissue from where the thrips have done their worst. Sometimes this can be confused with fungal or bacterial issues, but thrips damage tends to be more irregularly shaped and irregularly spaced.


Fungus gnats

These ones are fairly easy to ID, as they are small winged gnats in various colors of brown, gray, and black. They are not the same as the gnats that are attracted to decomposing fruit, but instead a highly specialized species that lays eggs in damp soil. Larvae can eat roots but they eat decomposing organic matter first. So, they are a problem if 1) there are too many of them and 2) they like to go up your nose while you're watching television. They will usually fly around the top couple of inches of soil from pot to pot and rarely stray from this area.


Fungus gnat treatment is fortunately one of the easiest!

  1. Let the soil dry out longer in between watering.

  2. Use sticky traps to catch flying adults before they can lay eggs.

  3. Use mosquito bits.

  4. Some systemic will prevent fungus gnats, too.

 

Pest ID Summary

  • Fluffy cottony sticky and white- mealys

  • Dust that doesn't come off, with webs and speckled leaves- mites

  • Sticky bumps that move, squishable or unsquishable- aphids or scale

  • Tiny, thread-like bugs, with irregular dying tissue on leaves- thrips

  • Flying gnats that like the moist warmth of your nose- fungus gnats

There are obviously so many more pests, but these are your most common.

 

General treatment

So, you found some bugs or suspect you have some bugs based on the damage going on to your plant. Do not panic! It'll be ok! Breathe in for a second and take a minute to process, then start on this little checklist below.

  • Isolate and prepare. You do not want to spread any pests to other plants. If there were other plants within a foot of the plant you suspect has pests, you will want to treat them too. Get your supplies together and don't work until you have the time to do so. Your plant won't die overnight.

  • Remove visible pests. Place your plant in a sink, tub, or outside and use a forceful stream of water to rinse away visible pests. Blast those suckers off! Tilt the plant sideways to prevent rinsing bugs on top of the soil (if you can). I will lightly rub the leaves if I know it will not damage the plant to do so, just to loosen any bugs that want to hold on tight.

  • Scale does not rinse off with water. Sometimes you need to use a soft cloth or a toothpick to carefully remove the pest from the leaf. My husband brought home this sad orchid covered in scale from his office so I could clean it up for its owner- I started by picking off all of the scale with a toothpick then scrubbing the entire plant with a washcloth and soapy water under the sink faucet.

  • Wash the leaves with a mild horticultural soap or even mild dish soap. I use my DIY neem soap.

  • Re-pot with fresh soil if the plant is heavily infested. I won't do this if I find a couple of mealy bugs. But in the case of the scale-infested orchid I certainly did. Wash the pot if you're re-potting.

  • Topical spray with horticultural oil, neem soap, or your preferred pesticide. Be sure to thoroughly coat every surface of the plant- above and below the leaves, the stems and petioles, rim of the pot, etc. Repeat every 3-5 days for at least 3 treatments, then as needed.

  • Add systemic granules or liquid to the soil. This is not an option for edible plants! Systemic pesticide is taken up by the plant through the roots and distributed throughout the plant. When a pest tries to munch or suck on the plant, it will die, and therefore it cannot reproduce. Systemic is crucial in treating pests that pop up consistently (such as mealys on my hoya, or thrips).

  • Monitor and inspect regularly. When you feel like the outbreak is controlled, put your plant back where it belongs and continue to monitor. Keep up on the prevention and mitigation routine to prevent further issues.

 

My personal experience with pests

I don't have many pests on my plants and I'm not just saying that. Healthy plants are actually able to fight off pests, pest damage, and disease much better than struggling plants- which is one reason why my collection doesn't have many issues. I focus on building healthy soil environments in every pot where plenty of beneficial microbes are doing their part to contribute to each plant's overall health.

I've also settled in to a routine that mitigates the lifecycle of most of the common houseplant pests. Some of my issues are seasonal- I get spider mite outbreaks in spring and summer when the air gets hot and dry, but I mitigate this by constantly wiping down leaves (or misting/spraying in the greenhouse) which controls their populations. My hoya collection will still see a mealy or two, but with the spot treatment and the systemic it's pretty smooth sailing and I never see any damage as a result. Pairing all of these practices with a good quarantine process for new plants has kept me from pulling my hair out over pests, which I know can be a huge problem for some houseplant hobbyists.


All in all, I've just come to terms that plants and bugs go hand in hand. And not just pests! I let spiders do their thing indoors and out. They are seriously a godsend for someone with a large plant collection. Most of the time you can't even see them, but they are helping you out-- if you let them.




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