Pests, webbing, and leaf spots on florist’s chrysanthemum

How to tell

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

The fix

Rinse the plant in the shower, wipe the leaves, raise humidity, 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 one leaf and wait two days before treating the whole plant, and skip any plant the label warns against. Isolate it from other plants.

How to tell

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

The fix

Dab each one with a cotton swab dipped in rubbing alcohol, then treat with a neem product made for houseplants, as its label directs. 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 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 tell

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

The fix

This plant must not dry out, so water from below to keep the surface drier, catch the adults on yellow sticky traps, and treat the soil with a Bti larvicide as its label directs.

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. Keep the soil evenly moist as this plant needs: 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. Florist’s chrysanthemum 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.