Pests and spots on cactus assortment: treatment

How to tell

Small, brown or gray, limpet-like bumps stuck to the stems, often with sticky honeydew.

The fix

Scrape them off gently with a fingernail or old toothbrush, then treat with a neem or horticultural-oil product made for houseplants, as its label directs, and keep checking. Test the spray on a small patch and wait two days before treating the whole plant, and skip any plant the label warns against.

How to get rid of scale →

How to tell

Fine webbing in the spines, tiny moving dots, and a stippled, dusty look to the stems. They thrive in the dry air many homes have.

The fix

Dab the stems clean with a damp cloth rather than rubbing them, give the plant good airflow, and treat with an insecticidal soap or neem product made for houseplants, repeating as its label directs until they are gone. Test the spray on a small patch and wait two days before treating the whole plant, and skip any plant the label warns against. Isolate it from other plants.

How to get rid of spider mites →

How to tell

Small black flies run across the soil and fly up when you water. Their larvae live in soil that stays damp.

The fix

Let the top layer of soil dry between waterings and catch adults on yellow sticky traps. A drier surface discourages egg laying and reduces egg and larval survival. If gnats persist, use a treatment labelled for fungus-gnat larvae on houseplants, following its instructions.

How to get rid of fungus gnats →

How to tell

Brown or black spots, often with a yellow halo, usually after the stems stayed wet or the soil was overwatered.

The fix

Remove affected tissue, improve airflow, don’t leave water sitting on the plant, and let the soil dry more between waterings.

How to tell

Bleached, yellow or brown patches only on the side that faces the sun, with no bugs or webbing. Cactus assortment wants bright light and some direct sun.

The fix

Shade it from the harshest midday sun for a few weeks, then let it back into the bright spot gradually.