Gray Mold (Botrytis)

• Gray-brown fuzzy mold coating fruit, flowers, stems, or dying leaves — the fuzzy texture is dense masses of spores
• Soft, water-soaked tissue beneath the mold that collapses when pressed
• Strawberries turning gray and fuzzy before or after harvest — the most familiar home-garden presentation
• Flowers turning brown and failing to open, or collapsing inward with gray fuzz developing at the base of petals
• Stems showing a tan, water-soaked canker at a wound site or where a dead leaf was in contact with living tissue
• Spore clouds releasing in a visible puff of gray powder when infected tissue is disturbed

Botrytis cinerea is a generalist fungal pathogen — it infects hundreds of plant species and is present in almost every garden. It overwinters on plant debris and in soil as sclerotia. Cool temperatures (55–75°F) combined with high humidity and wet foliage are optimal for infection and sporulation. The fungus typically enters through dead or dying tissue — a spent flower, a damaged leaf, a frost-killed shoot — and then spreads into living tissue from there. This makes it especially problematic in spring and fall, or in polytunnels and greenhouses where humidity stays high. Strawberries are a primary target because the fruit rests near the soil in a humid microclimate.

1. 01Remove and dispose of spent flowers, damaged leaves, and overripe fruit regularly — do not let decaying plant tissue accumulate; it is the primary entry point
2. 02Improve air circulation: thin dense plantings, remove crossing stems, and avoid planting susceptible crops too close together
3. 03Avoid overhead irrigation; water at the base of plants and water in the morning so foliage dries before nighttime temperatures drop
4. 04Mulch under strawberries to keep fruit off moist soil and reduce humidity in the canopy
5. 05For high-value crops in polytunnels: ventilate aggressively during the day and reduce humidity at night when possible
6. 06Bicarbonate sprays (potassium bicarbonate) applied preventively can suppress spore germination on fruit and foliage
7. 07Copper-based fungicides or Bacillus subtilis biocontrol products applied before periods of prolonged wet weather can reduce infection pressure on strawberries and tomatoes

If botrytis is destroying strawberry harvests or killing basil in your greenhouse every season despite reduced humidity and debris removal, a local extension specialist can advise on whether environmental management alone is sufficient or whether a preventive spray program is warranted.

• Botrytis (Gray Mold) on Vegetables— University of Minnesota Extension
• Gray Mold — Strawberries and Vegetables— UC ANR Integrated Pest Management