Common houseplant pests: fungus gnats, spider mites, mealybugs, scale and aphids

TUREFF• •0

Sooner or later almost every houseplant collection gets a visitor. Most pests can be dealt with without harsh chemicals if you catch them early. The trick is knowing what you are looking at and being patient, because nearly every treatment needs repeating to catch the eggs and young that the first round missed.

First steps for any pest

Isolate the affected plant from the others straight away.
Check its neighbours, including the undersides of leaves and where leaves join stems.
Wash it off: a shower with lukewarm water, or wiping leaves with a damp cloth, removes many pests on its own.
Inspect new plants carefully and keep them apart for a couple of weeks before they join the rest.

Fungus gnats

What you see: small dark flies, like tiny mosquitoes, flitting around the compost or a window. Adults are mostly a nuisance; their larvae live in damp compost and feed on fungi and decaying matter, occasionally nibbling roots of young plants. Why they come: compost that stays wet. What to do:

Let the top of the compost dry out more between waterings; this is the main fix.
Empty saucers and improve drainage.
Yellow sticky traps catch adults, which helps break the cycle.
Watering from below, or a layer of grit on top, makes the surface less inviting for egg-laying.

Spider mites

What you see: fine pale speckling on leaves, a dull, dusty look and, in bad cases, fine webbing at leaf joints. The mites are tiny. Tap a leaf over white paper and look for moving specks. Why they come: warm, dry indoor air, which is why they often appear in winter when heating is on. What to do:

Shower the plant regularly, paying attention to leaf undersides.
Raise humidity around the plant where possible.
Insecticidal soap or horticultural oil, applied thoroughly and repeated as the label directs, helps control them.
Heavily infested plants may be easier to discard than to rescue.

Mealybugs

What you see: white, cottony fluff in leaf joints, along stems and sometimes on roots, plus sticky honeydew on leaves. Their waxy coating protects them, so they are stubborn. What to do:

Remove visible ones by hand or with a cotton bud. Many growers dab them with rubbing alcohol; test on one leaf first, as it can damage some plants.
Spray with insecticidal soap, including leaf undersides, and repeat regularly until no new ones appear.
Check the roots if they keep coming back.

Scale insects

What you see: small brown or tan bumps on stems and along leaf veins that do not look like insects at all, and sticky leaves or black sooty mould on the honeydew. What to do:

Scrape them off gently with a fingernail or soft brush.
Wipe stems and leaves with a damp cloth or a little insecticidal soap.
Horticultural oil smothers young scale; repeat treatments are usually needed.

Aphids

What you see: clusters of small green, black or pale soft-bodied insects on new shoots and buds, often with distorted new leaves and sticky honeydew. What to do:

Squash or wipe them off, or rinse with a firm spray of water.
Insecticidal soap works well on aphids if it reaches them directly.
Pinch off badly infested tips.

Using sprays safely

Read and follow the label, and test any product on a small part of the plant first, as some plants are sensitive. Avoid spraying in strong sunlight. Many products, including some sold as natural, can be harmful to pets and fish, so keep animals away and store products securely.

Prevention

Healthy plants resist pests better. Give them the right light, water only when needed, wipe dusty leaves and look over plants each time you water. Catching a problem when there are five insects is far easier than when there are five hundred. Which pest gave you the most trouble, and what finally worked? Share your experiences or ask for help with an identification in the comments.