How to Identify Botrytis (Gray Mold)
Catching Botrytis cinerea in its first 24–48 hours is the difference between removing one leaf and losing an entire plant. Because the fungus attacks whichever tissue is weakest — a dying flower, a bruised leaf, a shaded lower branch — symptoms show up in different places depending on the plant and the stage of growth. Use the checklists below to scan your plants systematically.
Symptoms by Plant Part
Flowers & Buds
Petals turn translucent/water-soaked, then brown at the edges first
Fuzzy gray-brown mold forms on spent or damaged petals
Dense flower clusters (roses, buds) rot from the inside out — often invisible until you part the petals
A musty, damp smell before any visible mold appears
Leaves
Irregular brown, water-soaked lesions, often starting at the tip or a damaged edge
Concentric tan/brown rings ("target spot" pattern) as the lesion expands
Gray-brown fuzzy spore growth on the underside in humid conditions
Lower, shaded leaves affected first — airflow is worst there
Stems & Crowns
Water-soaked, sunken brown lesions girdling the stem
Stem snaps or collapses above the lesion under light pressure
White-to-gray mold visible at the base in soil-level infections
Black, hardened sclerotia (irregular seed-like lumps) inside split stems on severe cases
Fruit
Soft, sunken brown spots that expand rapidly, often starting where fruit touches soil or another fruit
Fuzzy gray mold coating within 2–3 days of the first soft spot
Fruit collapses into a mushy, watery mass with continued humidity
Concentric rings under the mold in early-stage lesions
How Symptoms Progress
- Day 0–1
Small, water-soaked, slightly translucent lesion. No visible mold yet — easy to miss or mistake for physical damage.
- Day 1–2
Lesion browns and expands. Tissue feels soft/mushy to the touch rather than dry or crisp.
- Day 2–4
Characteristic fuzzy gray-to-gray-brown mold layer appears on the lesion surface — this is the fungus sporulating.
- Day 4+
Spores disperse to neighboring tissue and plants. Left untreated, the lesion fully consumes the affected part, and new infections appear nearby.
Don't Confuse It With
Powdery mildew: White-gray, dry, powdery coating on leaf surfaces — no rotting or mushy tissue underneath, and it doesn't need high humidity to spread.
Downy mildew: Yellow blotches on top of the leaf with gray-purple fuzz only on the underside, following leaf veins — Botrytis attacks any tissue, not just leaf undersides.
Bacterial soft rot: Slimy, foul-smelling collapse with no fuzzy mold at all, and it spreads faster in warm conditions rather than cool ones.
Sunscald / physical damage: Dry, papery, tan patches with a defined edge and no expansion over time — Botrytis lesions are soft, spread daily, and eventually sprout mold.
Frequently Asked Questions
What does Botrytis look like at first?
The earliest sign is usually a small, water-soaked, light-brown lesion on a petal, leaf edge, or stem — often where two surfaces touch or moisture collects. Within a day or two under humid conditions, this develops the tell-tale fuzzy gray-brown mold coating.
Does Botrytis always look gray?
The mold itself is gray to gray-brown and dusty in appearance, but the underlying tissue damage can look tan, brown, or almost black depending on the plant and how far the infection has progressed. Young lesions may show no visible mold at all yet.
How is Botrytis different from powdery mildew?
Powdery mildew forms a white-to-gray powdery coating on the leaf surface without rotting the tissue underneath, and it thrives in dry conditions with high humidity only at night. Botrytis causes soft, water-soaked rot with a fuzzier gray-brown mold, and needs sustained high humidity to develop at all.
Can I confirm Botrytis without a lab test?
In most home and hobby settings, the combination of water-soaked tissue turning brown, followed by fuzzy gray-brown sporulation, in cool humid conditions, on damaged or dying plant parts, is diagnostic enough. A lab test is only needed for commercial operations confirming fungicide resistance.
