← The Green Windowsill: Houseplants Without Casualties
Lesson
Lesson 2. Pests: who lives on your plants
Recognize the main houseplant pests by the traces they leave (fine webbing, white cottony clumps, a sticky residue) and know the basic ways to fight them.
Pests leave clues
Who to look for, and by what traces
Many pests are tiny, but they leave noticeable traces. Here are the “big four” houseplant pests:
— Spider mites. Tiny dots on the undersides of leaves; the leaves get fine pale stippling and turn dull; in advanced cases, fine webbing in the leaf axils and at the tips. They love warm, dry air (radiators and heating vents in winter).
— Mealybugs. White cottony clumps in the leaf axils and on stems, like bits of cotton. The plant is sticky and grows slowly.
— Scale. Small brown bumps (“shields”) on stems and leaves that don't rub off with a finger; the leaves are sticky.
— Aphids. Clusters of tiny green, black, or whitish insects on young shoots and buds; a sticky residue.
A sticky, shiny residue on the leaves and under the plant (“honeydew”) is a common sign of sap-sucking pests (mealybugs, scale, aphids). If you see stickiness, look for whoever left it.
Lesson notes
Who to look for, and by what traces
Many pests are tiny, but they leave noticeable traces. Here are the “big four” houseplant pests:
— Spider mites. Tiny dots on the undersides of leaves; the leaves get fine pale stippling and turn dull; in advanced cases, fine webbing in the leaf axils and at the tips. They love warm, dry air (radiators and heating vents in winter).
— Mealybugs. White cottony clumps in the leaf axils and on stems, like bits of cotton. The plant is sticky and grows slowly.
— Scale. Small brown bumps (“shields”) on stems and leaves that don't rub off with a finger; the leaves are sticky.
— Aphids. Clusters of tiny green, black, or whitish insects on young shoots and buds; a sticky residue.
A sticky, shiny residue on the leaves and under the plant (“honeydew”) is a common sign of sap-sucking pests (mealybugs, scale, aphids). If you see stickiness, look for whoever left it.
Basic pest control
General steps that work for most houseplant pests:
1. Isolate the plant. Pests crawl over to the neighbors — put the sick plant “in quarantine” away from the others.
2. Physically remove what you can see. Mealybugs and scale come off with a cotton swab dipped in rubbing alcohol or soapy water. You can also rinse the plant under a lukewarm shower (cover the soil).
3. Treat. For mild cases, soapy water or insecticidal soap (a potassium soap); for serious ones, special products (insecticides; for mites, miticides). Often you need not one treatment but 2–3 treatments a few days apart, to kill the newly hatched generation.
4. Remove the cause. Spider mites love dry air — higher humidity and showers make life hard for them.
5. Prevention: keep new plants from the store separate at first and inspect them — pests most often come home with a new purchase.