Botrytis / grey mold

📖 Overview

Grey mold, caused by the fungus Botrytis cinerea, is one of the most common fungal diseases in temperate gardens, striking everything from strawberries and grapes to roses and salad greens. You'll recognize it by its distinctive grey-brown, velvety or cobweb-like fuzz that appears on flowers, fruits, and leaves—and when you touch it, a cloud of spores puffs away. This fungus thrives in cool, humid conditions, making spring and autumn the danger seasons, though it can flare up whenever wet foliage lingers too long. The first sign is usually small water-soaked spots that quickly turn soft and fuzzy, often starting on flower petals or wounded fruit.

Why it matters: Botrytis can wipe out an entire strawberry or tomato crop in wet years, turn roses to mush before they open, and make young lettuce unpresentable within days. In vineyards and orchards, it causes serious economic loss. Even a few infected fruits or flowers left untreated can spread spores throughout your garden, especially if you brush past wet plants or move them around.

The key to beating grey mold is prevention through air circulation and moisture management. Unlike many fungal diseases that hide in soil, Botrytis spreads primarily through airborne spores during damp periods—so good ventilation, removing dead flowers and damaged fruit promptly, and avoiding overhead watering in the evening are your strongest defenses. Once infection takes hold, organic and chemical options exist, but they work best when combined with these cultural practices.

Don't confuse Botrytis with powdery mildew, which produces a white, chalky coating that doesn't puff when touched, or with downy mildew, which shows yellow patches on upper leaves with a grey fuzz only on the underside.