Diseases & rots

Leaf spot (fungal & bacterial)

Round or angular spots, often with a yellow halo, spreading on leaves that stay wet.

What you'd see

Brown, black or tan spots, sometimes with concentric rings (fungal) or a water-soaked, angular look bounded by veins (bacterial)
Yellow halo around the spot
Spots merging into blotches; leaves yellowing and dropping

Where to look

Leaves that stay wet after misting or overhead watering; crowded, poorly ventilated spots. Common on dracaena, dieffenbachia, philodendron and monstera.

How it spreads

Splashing water and wet fingers carry spores and bacteria from leaf to leaf.

Is it really this? Look-alikes

Sunburn — Sunburn is a large pale or bleached area on the window side, not multiplying spots.
Edema — Edema is raised corky bumps on the underside, not sunken spots.
Fertilizer burn — Burn hits tips and margins, not scattered spots.

What's going on

Fungal and bacterial leaf spots both need a film of water on the leaf for several hours to infect. Misting, overhead watering and condensation give them that film.

Once inside, they kill cells in an expanding ring; the yellow halo is the leaf's chemical response around the dead zone.

Why?

The organism varies, but the requirement is always the same: standing water on the leaf. Keep the leaves dry and the disease has no doorway. That is why 'stop misting' is real advice, not folklore.

Grandmother's remedies

What people have always done — with an honest note on each.

Pick and bin
Remove spotted leaves with clean scissors; do not compost.
Verdict: Essential — spots are spore sources.
Chamomile tea spray
Cooled strong chamomile tea misted on foliage.
Verdict: Mild antifungal reputation, weak evidence; harmless.
Stop misting
Water the soil only; keep foliage dry.
Verdict: The single most effective action.

Modern remedies

What growers and extension services reach for today.

Copper-based fungicide
Per label, as a protectant on remaining leaves.
Verdict: Useful for bacterial and fungal spots on valuable plants; protects new tissue rather than curing old spots.
Improve airflow and spacing
Fan, spacing, and no water on leaves.
Verdict: Highly effective and free.

Honest verdict

Spots that are already there will not heal — the goal is no new ones. If new leaves come in clean after you change watering habits, you have won.

Prevention

Never mist plants prone to spotting
Water at soil level, in the morning
Space plants and move the air
Sterilise scissors between plants

Plants this commonly troubles

Monstera Pothos Fiddle-leaf fig Philodendron