Treating & Preventing Botrytis (Gray Mold)
Because Botrytis cinerea spreads through airborne spores and needs only humidity and dead or damaged tissue to take hold, treatment has two parts: stopping the current outbreak, and making your growing conditions permanently inhospitable to it. Skipping the second part is the #1 reason gray mold keeps coming back.
Immediate Treatment Steps
- 1
Isolate the affected plant from others immediately — spores travel on air currents and can infect neighbours within hours.
- 2
Cut out all visibly infected tissue with clean, sharp shears, including 2–3 cm of healthy-looking tissue beyond the visible lesion.
- 3
Bag and remove cuttings from the growing area immediately — do not shake, brush, or compost them, as this releases a new spore cloud.
- 4
Disinfect your shears with 70% isopropyl alcohol or a 10% bleach solution between every cut to avoid spreading spores yourself.
- 5
Drop ambient humidity below 60% RH and increase airflow with a fan — this halts new sporulation even on lesions you haven't found yet.
- 6
Apply a fungicide appropriate for Botrytis (see below) to the remaining plant as a protective measure.
- 7
Re-inspect daily for 10–14 days — new lesions can appear from spores that were already airborne before treatment began.
Treatment Options
Organic / Biological
Bacillus subtilis or Trichoderma-based biofungicides applied preventively
Potassium bicarbonate sprays on remaining healthy foliage
Diluted hydrogen peroxide (food-grade) wipe on hard surfaces and tools
Cinnamon or chamomile compost tea as a mild preventive spray for hobby growers
Chemical Fungicides
Fenhexamid or fludioxonil — labeled specifically for Botrytis on ornamentals/edibles
Copper-based fungicides for early-stage protection on outdoor plants
Rotate active ingredients between applications — Botrytis develops resistance quickly to repeated single-mode-of-action use
Always check the product label for your specific plant/crop and local regulations before applying
Long-Term Prevention
Keep relative humidity below 60% and run fans continuously for airflow, especially around dense foliage and flower clusters
Space plants so leaves and flowers aren't touching — Botrytis spreads fastest wherever surfaces stay in contact and stay damp
Remove spent flowers, yellowing leaves, and fallen debris promptly rather than letting them decompose in place
Water at the base rather than overhead, and water earlier in the day so foliage dries before evening humidity rises
Disinfect pots, trays, and tools between uses — sclerotia and spores can persist on surfaces for months
Avoid excess nitrogen fertilization, which produces soft, lush tissue that Botrytis infects more easily
Quarantine and inspect new plants for 1–2 weeks before placing them near your existing collection
Frequently Asked Questions
Can a plant recover from Botrytis?
Yes, if caught early. Removing infected tissue promptly and correcting humidity/airflow stops the spread, and the rest of the plant usually recovers fully. Once Botrytis has girdled a main stem or consumed a fruit/bud cluster, that specific part cannot be saved — but the plant itself often can.
What is the single most effective way to stop Botrytis?
Lowering humidity below 60% RH and improving airflow around the plant. Botrytis cannot sporulate or spread effectively in dry, well-ventilated conditions — this single change often does more than any fungicide.
Are fungicides necessary?
For a hobby plant or two, sanitation and environmental correction are usually enough. For dense plantings, greenhouses, or high-value crops, a preventive fungicide rotation is recommended because Botrytis develops resistance quickly to any single active ingredient used repeatedly.
How do I stop Botrytis from coming back next season?
Remove and destroy (don't compost) all infected plant debris, since sclerotia can survive in soil and decaying matter for years. Rotate crops where possible, disinfect tools and pots between uses, and space plants for airflow from the start.
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