Pests, webbing, and leaf spots on pinstripe calathea

How to tell

White, cottony fluff tucked into leaf joints and along stems, sometimes with sticky residue.

The fix

Test isopropyl alcohol of 70% or less on a small part of the plant first and wait 1–2 days to check for leaf damage. Then dab each one with a cotton swab dipped in it. If you use a neem product made for houseplants, follow its label. Test the spray on one leaf and wait two days before treating the whole plant, and skip any plant the label warns against. Check weekly: they hide.

How to get rid of mealybugs →

How to tell

Small, brown, limpet-like bumps stuck to stems and the undersides of leaves, 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 one leaf 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

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

The fix

Water only when the surface of the soil has dried slightly, from below if you can, so the surface stays drier. Catch the adults on yellow sticky traps and treat the soil with a Bti larvicide as its label directs.

How to get rid of fungus gnats →

How to tell

Silvery, shiny patches on the leaves, dotted with tiny black specks of droppings that wipe off. The insects are slim, 1 to 2 mm long, and run or drop when disturbed.

The fix

Move the plant to another room, rinse the tops and undersides of every leaf, cut off the worst leaves and treat in rounds with an insecticidal soap made for houseplants, as its label directs. Depending on the species, non-feeding stages shelter in the potting medium, plant crevices or on leaves. Sticky cards monitor flying adults. Keep checking for several weeks.

How to get rid of thrips →

How to tell

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

The fix

Remove affected leaves, improve airflow, and water the soil rather than the leaves, only when the surface of the soil has dried slightly. Wet leaves, not moist soil, spread leaf spot.

How to tell

Dry, bleached, or brown patches only where strong direct sun hits the leaf, with no bugs or webbing. Pinstripe calathea wants bright, indirect light.

The fix

Move it back from the glass, out of the strongest sun.