Houseplant pests and how to deal with them

If you have any plants in your house, there’s a good chance you’re pretty proud of them. After all, we plant parents tend to be slightly obsessive over our plant babies (see the more than 10 million posts under #plantsofinstagram), and this love for them also tends to lead us to worry when something is going wrong. Yellow leaves, shedding foliage, droopiness, odd white spots…these changes can spell trouble. While it might be a matter of too much (or too little) water or light, in some cases the foe you’re facing is more sinister – it’s the dreaded houseplant pests.

How did I even get these plant pests?

Good question! The annoying…well, pests, come into your home through a number of different avenues. They might be introduced via newly purchased plants or plants that have been outdoors, or could have caught a lift in via a pet, child, or the air. Unfortunately, there isn’t a lot you can do to control this. A certain level of vigilance is required when you have houseplants to keep on top of pest issues, but nothing too crazy. Checking them over once every few weeks should do the trick – and when you start noticing changes like yellow leaves, spotting, etc, then you know to spring into action.

Mealybugs

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Mealybugs are one of the more recognisable pests – it’s pretty hard to miss them when they’re a few millimetres across, grey or white, and when they are in their infancy, look like they’re covered in a white powder. They love hiding on leaves or in the grooves where leaves meet stems. Mealybugs will suck nutrients out of your plants, so they are often accompanied by yellowing leaves, stunted growth, and sick looking foliage.

Obviously, the clearest sign of a mealybug infestation is their infamous white powder coating. Baby mealies, otherwise known as crawlers, grow this coating to protect them from predators. You won’t miss a mega infestation of them! The aforementioned foliage changes are a pretty good indicator as well. Early signs that you might have a problem include small, line-like scars on leaves, a sticky brown substance on the leaves (‘honeydew’, or mealybug poo), or a lot of ants being drawn to the plant (they’re attracted to the honeydew).

How to deal with mealybugs

Given how easy they are to spot, it will be very clear which plants have an infestation of mealybugs. To stop this spreading, start by isolating the plant(s) that have mealybugs on them. You’ll then want to wipe the plant down gently with a soft cloth, removing every sign of the pest. Make sure you check under leaves, in the nooks where leaves attach to the stem, and down near the roots. After this, you’ll want to consider repotting the plant, as mealybugs will lay their eggs in the soil your plant lives in. Not repotting puts you at risk of the infestation re-emerging in a few weeks.

Thrip

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Thrip (known also as thunderflies or thysanoptera) look like teeny, tiny little flies or grasshoppers. They’re so small that most people mistake them for slivers, and only realise they’ve got a problem when the slivers start to move. They can range in colour from light green to white to yellow, black and brown. There are more than 7,400 species of thrips worldwide, but the most common species are greenhouse thrip, western flower thrip, and plague thrip. Thrips can be particularly insidious as they often spread plant viruses (for example tomato spotted wilt virus), so you can be in a position where you’re fighting a battle on two fronts.

You’ll notice thrips when you start seeing sections of your plant moving, or small holes appearing in the leaves. Streaks, silvery speckling, and small white patches might also be indicators of an infestation. Simply shaking the leaves or stem of the plant will let you see them hop or fly away, if you need to confirm.

How to deal with thrips

Thrips are both easy and hard to deal with. Easy, because a simple wipe-down will get most of them off the plant (considering they will fly/hop away), but hard because…well…they fly/hop away.

You’ll want to start this process by isolating the plant(s) with a problem. Wipe them down, then spray with neem oil, and determine if you need to repot. If you do repot, ensure you use a new or sterilized pot, new potting mix, and considering protecting the newly repotted plant by using either canna aqua clay balls (or similar), gravel or coir fibre matting over the top of your potting mix, as all of these act as a shield and can help prevent future infestations.

Fungal gnats

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Often mistaken for fruit flies, these pests area sign of a bigger problem. Fungal gnats are little flies with dark, slender bodies, and they eat fungi, the organic matter in soil and algae, all of which are common in houseplant pots. They love humidity, and temperatures between 17-25 degrees – which, unluckily, is the temperature of most Australian households.

You’ll probably notice your fungal gnat problem when you notice you’ve got a group of bugs following you around. Adult gnats love carbon dioxide, so they will hover around your face and annoy you. You might also have notice a fungi problem, which might indicate you’ve got a gnat problem. Fungal gnats are infamous for spreading fungal diseases such as Fusarium and Phytopthora, which will completely destroy your plant.

How to deal with fungal gnats

Obviously, you’ll need to isolate the plant(s). Then you need to wipe down the plant to remove anything that’s hanging around. Unfortunately, most fungal gnats will simply fly away at this step, but it gets you ready for the next step of the process. From here, you’ll want to spray the plant with neem oil (or whatever is preferable for the plant) liberally, covering all of the leaves and letting it soak into the soil.

Now you’ll want to consider repotting. Fungal gnats will lay eggs in your potting mix, meaning that if you don’t get rid of them now, you’ll be dealing with a re-emergence of the problem very quickly. You can use a brand new pot or sterilize the current pot for this step, but the most important thing you can do is use a fresh, high-quality potting mix – poor quality potting mixes can come with pests in them, which kind of defeats the solutions. To repot correctly, ensure you gently shake all of the old soil from your plants roots (away from your other plants, because fungal gnats can fly). Rinse the roots with a mix of equal parts neem oil, dishwashing liquid, and water. Repot the plant in the new/sterlised pot, pop in a yellow sticky card (otherwise known as gnat stix) and you’re all done.

Spider mites

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Spider mites are another instantly recognizable pest, simply because it’s very easy to see when webs start popping up on a plant. Although they are not actually spiders, spider mites look quite a bit like them with all of their crawling and web-making, but they feed by sucking all the nutrients out of your plant (and are not a threat to you at all!). They love indoor plants, and hot, dry air, making Australia an ideal location for them.

The most obvious sign of a spider mite infestation is their infamous webs, but you might also notice brown and yellow spotting on leaves, or patchy discolouration if the infestation has been left too long.

How to deal with spider mites

Step 1: isolate, isolate, isolate. We can’t say it enough. It’s the best way to ensure the infestation doesn’t spread to other plants, and to ensure that the infected plant can be treated effectively.

Step 2: Wipe the plant down. This step is particularly important when you’re dealing with spider mites, as you’ll want to take out any mites and/or webbing that you can see. Be sure to check under leaves!

Step 3: Hit that plant with some neem oil (or whatever natural pesticide is the best for the plant you are dealing with – some orchids, for example, might prefer rose pesticides as these are more effective). Repeat these steps as needed over the new few weeks.

Scale

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Lots of people dismiss this pest as natural leaf discolouration, but they couldn’t be further from the truth. Scale are small, oval shaped bugs with a protective covering that is white, translucent, or brown in colour. They lie flat on the plant (generally on the leaves) to suck the sap from the plant.

Scale are immobile once they decide on their forever home location. They lock themselves in place with their protective covering, which makes things much easier for you because it means that you’re not trying to chase any bugs around.

How to deal with scale

As always, first you need to isolate the plant(s) that have scale. Wipe over the whole plant with a soft cloth, gently scratching off any scale which don’t move during that first wipe-down. Make sure you check under leaves and in the small nooks where leaves attach to the stem. You’ll then want to wipe down the plant with an insecticide like neem oil, as this will prevent any new pests from being attracted to your plant. You’ll probably want to repeat this process at least once a week for at least three weeks, just to be safe.

Just remember that finding pests on your plants is normal, and it doesn’t make you a bad plant parent! Just crack down on the critters quickly and your plants will remain healthy.

Written: 1 June 2021

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