Brown Spots on Plant Leaves: Causes and How to Treat Them

What brown spots look like

Brown spots come in a handful of distinct shapes, and identifying the shape does most of the diagnostic work.

Round spots with a yellow halo, sometimes with a darker rim or concentric rings like a target, scattered across several leaves. Spots may merge into larger dead patches. This is the signature of fungal leaf spot.

Angular, water-soaked spots that stay within the leaf veins, look greasy or translucent at first, then turn brown or black with a yellow border. This is bacterial leaf spot.

Large, pale tan or bleached patches on the upper surface of leaves facing the window, dry and papery, with no halo. That is sunburn.

Brown tips and margins that are dry and crispy, with a thin yellow band between the brown and the green. This is fertilizer or salt burn, or a watering gap.

Dark, blotchy, water-soaked areas that appear overnight and later dry to brown, often on the most exposed leaves. That is cold damage.

Tiny specks, stippling or silver streaks with a dusty or sticky feel, usually on the undersides. That is pest feeding.

Brown spots are easily confused with white spots from powdery mildew or scale, with the natural brown “freckles” on some pothos and begonias, and with corky bumps from edema. Compare against a healthy leaf on the same plant before deciding.

What causes brown spots

Fungal leaf spot. Fungi such as Cercospora, Alternaria and Colletotrichum (anthracnose) land on wet leaves and grow into the tissue, killing it in a round patch. They spread by splashing water and thrive in humid, still air. The dedicated leaf spot guide covers treatment in depth.

Bacterial leaf spot. Xanthomonas and Pseudomonas bacteria enter through pores and wounds on wet leaves, producing angular, water-soaked spots that turn brown. Common on begonias, philodendrons, pothos and ivy, and much harder to stop than fungal spot once established.

Sunburn. Leaves that grew in shade or indoor light cannot cope with direct sun. Cells on the exposed surface overheat and die within hours, leaving pale, dry patches on the window side. Plants moved outdoors in spring and plants placed in a south or west window in summer are the usual victims.

Fertilizer and salt burn. Excess fertilizer, hard tap water and softened water build up salts in the soil, which draw water out of root tips and burn leaf edges. A white crust on the soil surface or the pot rim confirms it. Fluoride in tap water does the same to dracaenas, spider plants and peace lilies.

Cold damage. A night below about 10°C (50°F) for tropicals, or leaves pressed against winter glass, ruptures cells. The damage appears as dark, wet-looking blotches within a day and dries to brown or black over the following week.

Overwatering. Waterlogged roots cannot supply the leaf evenly, and leaf cells in the middle of the blade die in soft brown patches with yellow halos. The soil stays wet, and lower leaves yellow too.

Pests. Spider mites leave pale stippling that browns as it dries, with fine webbing underneath. Thrips leave silver streaks dotted with black specks that turn brown. Scale insects sit as brown bumps on stems and leaf undersides and can be mistaken for spots until you flick one off.

Edema. When roots take up more water than the leaf can release, cells burst and heal as corky brown bumps on the underside. It is a watering and humidity problem, not a disease, and common on peperomias, ivy and succulents.

Match the pattern to the cause

What you see	Most likely cause	Confirm it by
Round brown spots, yellow halo, sometimes target rings, several leaves	Fungal leaf spot	Spreads to new leaves; worse after misting or wet weather
Angular, water-soaked spots between veins, yellow edge	Bacterial leaf spot	Greasy look when fresh; spreads fast in humidity
Pale tan, papery patches on the window-facing side	Sunburn	Only exposed leaves; recent move or sunnier season
Crispy brown tips and margins, thin yellow band	Fertilizer or salt burn	White crust on soil; regular feeding or hard water
Dark, wet blotches overnight, later brown	Cold damage	Near a window or door; cold night on the forecast
Soft brown patches mid-leaf with halos, lower leaves yellow	Overwatering	Soil wet 3 or more days after watering
Stippling, silver streaks, webbing or sticky film	Pests	Insects or webbing under a magnifier
Raised corky bumps on the underside only	Edema	Wet soil plus cool, humid air

How to treat brown spots

1. Isolate the plant if the spots look fungal or bacterial, so splashing water and touching hands do not carry it to neighbors.
2. Remove affected leaves. Cut any leaf that is more than a third damaged, or any leaf with spreading spots, at the stem with scissors wiped in 70% isopropyl alcohol. Bin them; do not compost. Clean the scissors between plants.
3. Keep the foliage dry. Stop misting, water the soil rather than the leaves, and water in the morning so any splashes dry quickly. Increase airflow with a small fan or by spacing plants further apart.
4. Treat fungal spot. Spray all leaf surfaces with a copper-based fungicide or a neem oil solution of 5 ml per liter of water with a few drops of dish soap, in the evening or out of direct sun. Repeat every 7 days for 3–4 weeks and watch new growth. For bacterial spot, copper sprays slow the spread but rarely cure it, so removing infected leaves quickly matters more.
5. Fix sunburn by moving the plant. Shift it 1–2 m (3–6 feet) back from the glass or hang a sheer curtain. Acclimate plants to brighter light over 2 weeks. The burnt patches stay; new leaves will be fine.
6. Flush salts. Run water through the pot equal to two or three times its volume and let it drain completely. Repeat monthly if you feed often. Feed at half the label strength every 2–4 weeks in the growing season only, and use rainwater or filtered water for fluoride-sensitive plants. Brown leaf tips that persist point to the water rather than the food.
7. Treat cold damage by moving the plant to a spot that stays above 15°C (59°F) and trimming tissue that has gone soft or black. Hold fertilizer until new growth appears.
8. Correct the watering if the soil stays wet. Let the top 2–3 cm (1 inch) dry between waterings, empty saucers, and repot into a chunkier mix if the soil stays soggy for days.
9. Treat pests with a thorough wipe-down followed by neem oil or insecticidal soap on every surface, repeated every 5–7 days for 3 weeks. Dab scale with a cotton swab of 70% isopropyl alcohol.

Prevention

Water the soil, not the leaves, and give plants enough space that air moves between them. Skip misting for anything prone to leaf spot; a humidifier raises humidity without wetting the foliage.

Introduce plants to brighter light gradually, and pull tropicals back from the glass in midsummer and midwinter. Flush pots every 2–3 months if you use tap water or feed regularly.

Quarantine new plants for 2 weeks and check the undersides of leaves when you water, so pests and the first spots are caught while one leaf is affected rather than ten.

When to use AI diagnosis

Fungal, bacterial and watering-related spots can look nearly identical in the early stages, and treating a bacterial infection like a sunburn costs you weeks. If the spots have halos, are appearing on new leaves, or are spreading to nearby plants, photograph a spotted leaf up close in the AI Plant Doctor app for an instant diagnosis and a treatment plan matched to the actual cause.