PLANT PESTS
Houseplants can be troubled by small, unwelcome guests that can damage and even kill them. Here’s how to identify the signs of a pest infestation, and what you can do to save your plant.
HOW TO STOP PESTS
The best way to avoid pests is to keep your plant healthy—pests are more likely to attack stressed, unhealthy plants. If your plant does become infested with a pest, in many cases you will be able to treat it with an insecticide, either chemical or natural. Natural products are derived from plants or other natural substances.
Sticky traps are especially good for trapping aphids, whiteflies, and thrips, and can help you monitor the level of infestation.
If you have a lot of houseplants in one place that are all suffering from the same problem, you could try a biological control. These natural products are available by mail order and work by introducing predators (usually invisible to the naked eye) to attack the pests.
THE PESTS
You may find signs of these pests on your houseplants. Plants that are particularly prone to infestation will have more details on their care page.
WHITEFLIES
They hide on the undersides of leaves, and clouds of tiny white insects will fly up when your plant is disturbed.
TREAT IT: Take your plant outside and dislodge the insects with a spray of water; you could also dunk the whole plant in a bowl of lukewarm water. A sticky trap hung near the plant will trap a lot of insects.
FUNGUS GNATS
Also known as sciarid flies, these tiny brown or black insects fly around the plant. They aren’t harmful, but they are annoying. Their maggots mostly feed on organic matter in the potting mix, but can sometimes attack roots. Healthy plants can withstand this, but young or weak ones won't.
TREAT IT: Allow the top 1/2—3/4 (1 -2Cm) of potting mix to dry out before watering—this suits most plants, anyway. A yellow sticky trap will attract the insects away from your plant. Cover the surface of the potting mix with a mulch of fine gravel or pebbles to prevent the gnats from laying their eggs.
LEAF MINERS
Look for brown, white, or opaque meandering trails on the leaves, where the grubs have ”mined” them. There may also be white dots on the leaves.
TREAT IT: Remove the affected leaves. Spray with an insecticide.
THRIPS
Also known as thunder flies, these tiny brown or black sap-sucking insects may be seen on plants that have spent time outdoors. Signs of infestation include dull, mottled leaves, silvery white streaks on the leaves or flowers, and distorted growth.
TREAT IT: Sticky traps – especially blue ones – can reduce their numbers and can help you monitor the problem. Spray your plant with insecticide or try a biological control.
SPIDER MITES
Look for bleached or speckled foliage, webbing between the leaves and stems, and leaf fall. If you look under the leaves with the aid of a magnetifying glass, you’ll see the mites.
TREAT IT: Spray with an insecticide or use a biological control. Spider mites thrive in hot, dry conditions, so mist your plants daily to raise humidity if the atmosphere is hot and dry. Be vigilant – use a magnifying glass to look for the mites on the underside of leaves.
VINE WEEVILS
If your plant has collapsed and you haven’t over-or underwatered it, vine weevil grubs could be the culprit. They’re found in the potting mix of plants that have spent time outside. They munch on the plant’s roots, bulb, or tuber, causing it to suddenly wilt.
TREAT IT: If your plant has been outside in summer, drench the potting mix with an insecticide or biological control in the late summer or early fall to kill any grubs. If they have eaten most of the roots, your plant will not recover.
APHIDS
Also known as greenflies, these can be green, black, gray, or orange. They gather on the tip of the suck sap and secrete honeydew, which is then colonized by sooty mold. Aphids can also spread viruses.
TREAT IT: Rub them off by hand, dislodge with a spray of water, or spray with insecticide. Hanging a yellow sticky trap nearby can help.
SCALE INSECTS
These limpetlike insects look like brown lumps on the stems and the underside of leaves. They also excrete a sticky sap, which can lead to sooty mold. If not controlled, your plant will be weakened and the leaves will turn yellow.
TREAT IT: Rub them off, or spray the affected areas with insecticide (don’t spray the leaves of ferns, as they are very sensitive to chemicals). You could also try a biological control.
MEALYBUGS
These white, slow-moving insects coated in white fluff are found in clusters on stems, in leaf joints, and under leaves. They suck sap and excrete sticky honeydew, which then gets colonized by sooty mold. An infestation can lead to yellowing leaves, leaf fall, and wilting.
TREAT IT: Wipe off the insects with a damp cloth or cotton swab soaked with insecticide. Alternatively, spray the whole plant with insecticide once a week. You could try a biological control. Mealybugs are hard to eradicate and it is often simpler to throw away severely infested plants.
