How to Check A Houseplant For Pests

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It’s all very well having someone tell you to check your houseplants for bugs, but how exactly should you go about it?

The good news is that when you’ve been in the game as long as I have (about four years), you…just know.

I can usually spot the signs *just* before there’s any real damage done.

I've also become the master of ignoring pest problems, which is not advisable, but you know when you're stressed and tired but you need to water your plants? 

And then you see that your plant is looking a bit sad (a brand new leaf emerging brown is a sure sign) and you just know but cba to deal with it?

I’m great at that. That can be a problem for future Caroline, even though I know it’d be WAY easier for present Caroline to sort it out now. Future Caroline gets a raw deal.

Buuut when you’re a newbie, it helps to have steps to follow when some helpful person on Facebook or Reddit tells you to check for pests.

This is the order I go in, and it’s a combination of places where pests are most likely to be and places where pests are easiest to see.

Check all new growth

Adult thrips especially prefer new growth, so always keep an eye out for little black things that look like grains of rice on any new leaves.

They also LOVE to eat leaves that haven’t yet properly emerged, which is one of the reasons new growth often emerges brown and er, dead.

This little trick thrips pull is annoying, because if you’re not extremely careful when spraying for pests, you can end up damaging the delicate new growth.

I assume they like new growth because it’s so delicate. It makes it easier for them to extract the juices.

Check the back of the leaf

After I’ve checked the new growth, I check the back of the leaves. I don’t know why pests prefer to congregate on the back rather than the front, but I’m guessing the front of the leaves are a little harder to puncture than the backs, because the fronts will need more protection from the sun.

It also makes sense that pests would stay on the backs on the leaves because that'll offer them more protection from predators (mainly other insects). 

Also, the front of the leaf might be covered in a layer of dust, which though attractive to some pests, will put other ones off.

Here’s some thrips damage on the back of a Manjula Pothos leaf:

Check the front of the leaf

After you check the back of the leaf, check the front. Makes sense, no?

In my experience, thrips hide around the back of the leaf, but spider mites hang out around the front. Also, for some reason, thrips prefer the front of my Anthurium Clarinerveum to the back EXCEPT they also like to hang out around the back where the leaf lobes meet.

I went to take a photo to show you what I mean and GUESS WHAT I FOUND:

FFS guys.

Check in the petiolar sheath

Monstera are thrips magnets, and they like to hang out in the petiolar sheath. Mealybugs are also known for hanging out in anything resembling a crevice, so the bit of a Monstera leaf where the next leaf grew is perfect for them

Check where the leaf meets the petiole

The petiole is the stalk that attaches the leaf to the stem. At the very top, where the leaf meets the stem, is where spider mites like to hang out. Also thrips and mealybugs.

I believe it’s called a geniculum, but I’m not sure if it’s called that on every plant. Anyway, check there. Found a mealybug on my Calathea velvet touch in that very spot a couple of weeks ago.

Add yellow/blue sticky traps

Yellow traps attract fungus gnats, blue traps attract thrips. I personally don’t think they’re that efficient at eliminating these pests, because they only attract the mobile ones, so the eggs/larvae are unaffected.

However, if you’re not sure if you have either of these pests, try adding the sticky trap and seeing if you have any takers.

Wipe the leaf down with a white paper towel

I tend to use this trick mostly when I have suspected spider mites, because spider mites are invisible to the naked eye until they’ve built up a significant population. They’re most likely to crop up in hot windows – I got them from the baby plants I bought from the garden centre, which is why you should isolate new plants.

My baby rubber tree gets a lot of sun (she likes it!) so was a spider mite magnet. I confirmed the infestation by wiping the leaves with a damp paper towel. You basically smear their bodies and get a rusty-coloured smear on your towel.

They like to hide in crevices, but like heat, so the weird-shaped leaves of baby houseplants is their dream location:

The circled crevice is an awesome spider mite spot.

How to identify the bug

‘Bad’ houseplant pests are usually pretty slow-moving. You can see them moving, but they’ll be moving slow enough for you to catch them. The exception to this is adult thrips that can jump like fleas.

Mealybugs are a type of scale so they pretty much stay in place.

Here’s what they look like:

You can’t actually see spider mites without a magnifying glass, but you can see their webs. It looks like, er, webbing, and is finer than spider’s webs. I destroy any webs I find unless the spider is present just in case. Spiders will rebuild their webs if necessary, though I do feel bad.

What to do next

I’m a big fan of castille soap in a spray bottle. It keeps after you’ve made it up and it’s cheap. It’s less than a tenner for a big bottle. Just add a drop (say, a quarter teaspoon) to a spray bottle (I think mine is 250ml) and spray liberally over your plant. It smells good too. Repeat twice a week for a month and then check the leaves again carefully.

I used to use neem oil, because it works as a preventative, but I got sick of wasting it (it congeals if you don’t use the whole bottle) and I love that the soap os always ready to go.

I do use neem oil when cleaning my plants though, just as an extra preventative measure.

Final thoughts

I always check for pests if I see a decline in my plants but I haven’t changed anything. The most telling signs are new growth being stunted and weird, or no new growth at all.

Houseplant pests are pretty inevitable if you have a lot of plants, so it’s good practice to get into the habit of checking them over regularly so you can stop a future infestation from getting a foothold.

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

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