Swiss cheese plants are more prone to pests than diseases. The Swiss cheese plant pests are the usual ones found on houseplants and plants grown in greenhouses. Think scale insects, thrips and mealybugs. As for diseases, there are none that are exclusive to Swiss cheese plants. But I’ve included the ones most common to plants like the cheese plant, including root rot and powdery mildew.

If you have issues with the leaves turning yellow, this guide is probably the guide you need.

Swiss cheese plant pests

Scale insects

About scale insects

Scale insects are becoming more common and there are about 25 species of them of different sizes. So it’s no surprise that they are sometimes found as Swiss cheese plant pests.

All scale insects have a hard waxy shell that protects them somewhat from spray insecticides. These bugs feed by sucking the sap from the plant’s leaves and stems. In rare cases, if you get a serious infestation, it can lead to dieback. But it’s usually easy to catch them when there are just a few if you monitor your plants.

What to look for

Look for small (just a few millimetres) brown flecks on your plant leaves and stems. Check the underside, as the scale insects like to hang out there. It’s easier to see them if they’re in a group. Don’t hesitate to use a magnifying lens to investigate your plant thoroughly.

The first sign is that your leaves are turning yellow and wilting, even dropping off the plant. However lack of water can also cause this symptom. Another sign is a clear sticky substance called honeydew that the scale insects leave behind after eating your plant. But several other pests, including aphids, also do this, so it’s not definitive of scale insects.

What to do

If your cheese plant has just a few scale insects on it, pick them off, one by one. If the infestation is of quite a few bugs, try a spray of natural insecticide oil such as pyrethrum, or neem oil. Synthetic pesticides are a last resort. Try to get the active nymph scale insects in the summer as they’re at their most vulnerable then as they don’t have the waxy shell thats protects them.

Mealybugs on swiss cheese plants

About mealybugs

Mealybugs are another of the plant pests that enjoy sucking the sap from the leaves of your plant. This weakens your Swiss cheese plant, leading to its poor health. A few mealybugs are really no problem but a few quickly develops into dense colony that overruns your cheese plant.

What to look for

As mealybugs aren’t small, you can see them. But they do hide away in the leaf sheaf and in the outside layers of the stem. As they tend to group together, they’re a bit easier to spot.

These insects are also one of the types that leave behind honeydew. So look for patches of a clear, sticky substance of your plant. While this could indicate that mealybugs are around, it could also point to scale insects, so further investigation is needed.

What to do

First of all, isolate your plant. Place it in quarantine away from other plants of any kind. Remove the parts of the cheese plant that have mealy bugs on them and burn them. Don’t place the diseased bits in your compost pile as these pests really do spread quickly.

Look carefully for mealybugs on any plants that were close to the infected plant. Mealybugs spread fast, but they don’t go very far.

That’s it. If the mealybugs have hold of your plant, there’s nothing to do but destroy it.

Glasshouse red spider mites

About glasshouse red spider mites

Yet one more of the Swiss cheese plant pests that goes after the sap in your plant. You can see these mites as tiny red blobs on your plant’s leaves. They’re not really noticeable until they cluster together to form bright red blotches that are unmissable. Glasshouse red spider mites are active in the hot months of the summer.

What to look for

Look for these red splotches and also patches of the clear and sticky honeydew they leave behind. The leaves may be ravaged and mottled and even fall off the plant. Look closely and you may also see fine spider webs.

What to do

Red spider mites like an environment that’s hot and dry. As Swiss cheese plants like quite a high humidity, keeping a moist environment for the plant deters these bugs. Use a natural insecticidal soap or spray on the red blotches, or try neem oil.

Remove infected leaves and cut off infected stems. If the infection has spread to much of the plant, remove it entirely from other plants. In the autumn, the spider mites look for a home for the winter so keep the plant isolated. You may even need to destroy the cheese plant if it’s covered in too much red.

Thrips

About thrips

And yet another sap-sucking pest are thrips. Very small in size, these brown, black or tan insects have feathery wings in the adult stage. As these pests are almost microscopic in size, get out your magnifying lens to search for them. As well as damaging the plant, thrips also spread disease so they do double the damage.

What to look for

It’s easier to search for the damage thrips do than to see them themselves. If you notice a silver-coloured discolouration on the Swiss cheese plant leaves, then it has thrips. In addition, your foliage becomes super-thin where they’ve sucked the sap out of it.

What to do

Thrips seem to be attracted to blue. Hang a strip of blue sticky tape from your cheese plant to attract thrips to it. Hopefully, you’ll need to change the tape often as they thrips become stuck there.

Use a natural insecticidal soap or a natural oil such as pyrethrum or neem in a spray on the plant.  These are safe to use indoor but you need to keep reapplying them as they have a short work-life.

If you do have to use an insecticide as a last resort, choose one that has the organic ingredient pyrethrin (it comes from chrysanthemums).

Bear in mind that by the time you notice the damage that thrips have done, they may have moved off to another plant. Check all of your houseplants to see if they have thrips, and treat them accordingly. Once you have a thrip-free household, carefully check over any new plant that you bring in.

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Swiss cheese plant diseases

I’ve included here two diseases that many plants get, and Swiss cheese plants are no exception.

Root rot

About root rot

Root rot is a fungal disease that makes its home in wet plant roots. And the roots are usually wet because (a) you’ve overwatered the plant and/or (b) you’re using a soil mix that holds too much water and/or (c) there are not enough drainage holes in the base of the plant pot.

Saturated roots are not able to process oxygen. This prevents them from being able to circulate water and nutrients around the plant, and the plant becomes starved.

What to look for

The early signs of root rot are underground in the soil and so are not usually noticed. One of the signs of root rot is after it’s moved up the stem of the cheese plant. The stem becomes soft and mushy and may bend over, unable to hold up the leaves. In addition, you also see signs of overwatering, including yellow but full leaves. But by then, the root rot is fully established.

Uncover the roots of your Swiss cheese plant, If the roots are firm and green, you’re OK; root rot hasn’t moved in. But is the roots are soft and squishy and have turned black or brown, then your plant has root rot.

Another sign is that the potting mix is wet and waterlogged, not just nicely moist.

What to do

You need to uncover all the roots of your cheese plant. Take it out of the pot and remove all the potting mix. Sterilise your cutting tool and cut away all the diseased, dying or dead roots. This may leave you with just a few roots.

Dry out the plant pot. Add a few more drainage holes in the base. Put in all new (and dry) potting mix.

Repot the cheese plant. Thoroughly water the plant letting all the excess water drain out completely.

Change your plant watering regime so you only water the plant when the top 3cm or so of the soil is dry.

Powdery mildew

About powdery mildew

Powdery mildew is a very common fungal disease that usually hits outdoor plants. However, indoor plants are also susceptible to it as the spores are carried in the air. It often appears in dry and warm weather, and loves an environment with poor air circulation. The disease isn’t fatal but it takes away from the glossy look of the Swiss cheese plant leaves.

What to look for

Powdery mildew starts out as spots on the top of the plant’s leaves that look like white talcum powder. It can spread to the underside of the leaves and the stems. The splotches join up into irregular shapes and may eventually cover the entire leaf. It’s easy to identify.

What to do

Remove the infected portions of the plant using a sterilised cutting tool. Use a fungicide containing copper. This also serves as a preventative against future infestation.

And work on preventing the powdery mildew in the first place. Don’t water your cheese plant from the top of the plant – water right into the soil. Improve the air circulation around the plant. Keep a humid environment around your plant. And use a solution of neem oil and water as a spray over the cheese plant.

Don’t mist an infected plant as that carries the spores in the water droplets.

I also have a guide on why the leaves on Monstera sometimes droop here as well as why the leaves also sometimes curl.

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