Indoor Plant Pests & Diseases —
And How to Tackle Them
More indoor plants die from improper care than from disease or pest attack. But when trouble comes, knowing what you are dealing with — and acting quickly — makes all the difference.
While indoor plants are not prone to massive pest infestations like their counterparts growing out in the garden, indoor plants can develop many problems — and these problems are mostly cultural or environmental in origin.
Diseases are not common on indoor plants because the environmental conditions are rarely ideal for pathogens to grow and attack. Nevertheless, there will always be a chance that your plant collection could come under disease or pest attack — and the wise indoor gardener knows what to look for and how to respond.
In this guide, we outline how to forestall and manage the most common indoor plant pests and diseases — from the first signs of trouble through to treatment and recovery.
More indoor plants die from improper care than from disease or pest attack. Vigilance and sanitation are your greatest weapons.— Crystal Gardens Care Guide
How to Prevent Indoor Plant Pests & Diseases
Control begins with prevention. Your two greatest weapons are vigilance and sanitation.
Start with Healthy Plants
No amount of care will save plants that arrive already infected. Always source from reputable nurseries and inspect carefully before purchase.
Sterilise Soil & Pots
Plain garden soil carries pathogens. Use sterilised commercial potting mix. Scrub old pots and rinse in 1 part bleach to 9 parts water before re-use.
Quarantine New Arrivals
Isolate new or gifted plants for a few days before placing them among your collection. This gives you time to spot any problem before it spreads.
Ensure Air Circulation
Arrange plants so there is ample airflow between them. Leaves should not touch each other — this prevents disease spreading from plant to plant.
Inspect Regularly
Check stems and undersides of leaves where insects hide. Once you spot infection, isolate the plant immediately to prevent spreading to others.
Isolate or Discard
If a plant cannot be redeemed, discard it — however expensive it was. One severely infected plant, left untreated, can compromise your entire collection.
Common Indoor Plant Pests
Aphids
Aphids are soft-bodied, sap-sucking insects — yellow, green, black, brown, or pink depending on the species, with some winged and many not. They attack the soft parts of the plant: undersides of leaves, buds, and stem tips. Unlike many other pests, aphids are visible to the naked eye.
Aphid attacks are identified through leaves that curl, deformed new buds, and poor-looking foliage. They exude a sticky substance on which sooty mould can grow — a secondary problem that develops quickly if the original infestation goes untreated.
First spray them off with a hose. If the plant cannot be moved outside, wipe leaves and stems with a damp cloth weekly. For widespread attacks, apply organic insecticides containing rotenone and pyrethrin, or use a contact or systemic insecticide.
Whiteflies
The first sign of whiteflies is pale leaves that turn yellow and fall off. You will not see them with the naked eye, but under a magnifying glass they are clearly visible. It is at the larval stage that they cause the most damage. In adulthood, they fly out in clouds whenever the plant is disturbed.
They exude sticky honeydew and cluster on the undersides of leaves. They are lethal and will kill a plant if left untreated. Most susceptible: geraniums, fuchsias, chrysanthemums, poinsettias, and lantanas.
Use systemic insecticides containing pyrethrin. Apply weekly to eradicate the population — catching them in the nymph stage is most effective. Do not breathe in the spray, and apply when temperatures are 50–70°F.
Scale Insects
Scale insects are brown or yellow in colour and are found on the undersides of leaves. When young, they move around but are too tiny to notice. In adulthood, females remain stationary in visible clusters on leaf and stem undersides, enclosed in waxy covers.
Signs of a scale attack include light-coloured spots on leaves. Flip the leaf over and you will find scales underneath. Observant plant keepers will notice them before serious damage is done.
Treat using a toothbrush and warm water — scrub them off directly. Repeat over several weeks to catch newly emerging insects. If the infestation is widespread, discarding the plant may be the most practical solution.
Mealybugs
Mealybugs are oval-shaped and about ¼ inch long — they resemble bits of cotton clumped together on a stem or crown. They are covered in a sticky white substance that repels water, and they thrive in dark spaces away from direct light.
They exude sticky honeydew, causing leaf drop, and may cause a flowering plant to drop its buds entirely — making the plant look stunted and unhealthy overall.
Rub a cotton swab dipped in rubbing alcohol directly on each cluster of bugs, then rinse the plant afterwards. Alternatively, drench the potting mix with a systemic insecticide applied fortnightly until the infestation clears.
Snails & Slugs
These pests hide during the day — check under the pots and along the rims. They range from 1½ to 4½ inches in size. At night they emerge to feed on leaves, leaving a distinctive trail of silvery shine behind them that is unmistakable once you know what to look for.
Practice good sanitation — remove all dead leaves. Pick snails and slugs off the plant immediately when spotted. If you prefer not to handle them, place a saucer of beer or grape juice near the plant — the aroma attracts them and they drown. Alternatively, wrap copper wire along the side of the pot: copper gives them a mild shock on contact and acts as a very effective deterrent.
Spider Mites
Spider mites are sap-sucking mites that leave a fine silky web on the undersides of leaves. They are barely visible to the naked eye — you will usually only notice their presence through the fine webbing they leave behind.
They cause mottling of leaves, stunt plant growth, and eventually cause complete leaf drop. By the time webbing is clearly visible, the infestation may already be well established and require immediate action.
Spray with insecticide on both the upper and lower surfaces of all leaves. Repeat treatment is essential, as spider mite populations recover quickly if not fully eradicated in the first round of treatment.
Indoor Plant Diseases
Anthracnose
Anthracnose is caused by the fungi Colletotrichum and Gloeosporium. The leaf tips turn yellow, then dark brown — the browning can spread all around the leaf, and leaves eventually die off entirely.
Wounding of a plant — physical damage, poor handling, or rough re-potting — significantly enhances penetration of the fungus into plant tissue and accelerates spread.
Pick off all affected leaves and destroy them. Do not mist leaves during an outbreak — moisture on the leaf surface promotes the spread of fungal spores and will worsen the infection.
Fungal Leaf Spot
Leaf spot manifests as brown spots with yellowish margins on the leaves — appearing as concentric rings or target patterns. The leaves wither and die, and you will also notice small black spots visible in dead tissue.
These fungi survive on dead and decaying plant matter in the soil, and the disease is especially common where the air is persistently humid.
Provide good air circulation around all plants. Avoid splashing water directly onto leaves, as this spreads fungal spores. Remove all infected leaves promptly. If badly affected, discard the plant. As a preventive spray, apply zineb or benomyl.
Root Rot & Stem Rot
A root-affecting disease that causes leaves and stems to wilt. Stems may be girdled at the soil level by a ring of black or brown tissue. Infected areas will be brown to black and may feel soft to the touch.
The key culprit fungi — Rhizoctonia, Alternaria, and Sclerotinia — survive in the soil or infected plant debris. Spores are spread by wind, splashing water, or contaminated soil.
Use sterilised soil and clean pots. Avoid over-watering — it is the primary cause of root rot. If only a few roots are infected, cut them off and re-pot in treated or sterilised soil. Fungicides may help but can cost more than the plant itself — prevention is by far the better strategy.
Bacterial Leaf Spot
Plants infected with bacterial leaf spot display water-soaked spots with a yellow halo, uniform in size, sometimes with a sticky ooze. Under wet conditions those spots enlarge. Under dry conditions they do not enlarge — instead they dry out and turn reddish-brown, giving a speckled appearance.
Remove all diseased plant material promptly. Avoid low temperatures, overcrowding plants, and splashing or spraying water directly onto foliage — wet leaf surfaces are the primary route of infection spread.
Powdery Mildew
Mildew manifests as white, powdery patches on the surface of leaves. The leaves become distorted and may drop off. The most susceptible plants are soft-leaved varieties and those with succulent stems — they offer the least natural resistance to fungal colonisation.
A regular spray with an appropriate fungicide will help contain and clear the infection. Improve air circulation around the plant and avoid conditions of excess humidity, which promote the spread of spores and allow the disease to take hold more quickly.
Root, Stem & Crown Rot
This condition is caused by saturated potting soil combined with low temperatures. The root, stem, and crown rot — with affected areas becoming mushy, soft, and slimy. It is one of the most fatal of all indoor plant diseases and often cannot be reversed once well-established.
Cut out the affected area if possible. Although fungicides may provide some help, they will not cure a heavily infected plant. Prevention is the only reliable strategy: never allow pots to sit in waterlogged soil, ensure good drainage at all times, and maintain appropriate temperatures for your plant species.
Act Early. Act Decisively.
If you observe good preventive measures — starting with healthy, disease-free plants, using sterilised soil, quarantining new arrivals, and inspecting your collection regularly — the chances of a serious pest or disease problem remain very low.
When trouble does arrive, the outcome depends entirely on how quickly you identify it and how decisively you respond. Isolate, treat, and if necessary, discard. A single sick plant that is allowed to remain among a healthy collection is a risk that is never worth taking.
Your indoor garden, managed with vigilance and care, will remain healthy, beautiful, and rewarding for years to come.