Marigold Blackening: Botrytis Blight Identification and Organic Treatment

Blackening marigolds in cool, wet weather (62-72°F) strongly suggests Botrytis cinerea (gray mold).

Confirmation Test

Place affected tissue in plastic bag with wet paper towel. Gray mold appears in 1-2 days if Botrytis.

Immediate Isolation

Separate affected pots immediately. Spores spread easily to neighboring plants.

Cultural Corrections

• Water at soil level only (morning)
• Bring pots in at night/rain
• Keep dew off foliage
• Bottom-water only

Organic Treatment Duo

1. Serenade (Bacillus subtilis): Beneficial bacteria consumes fungal pathogens
2. Messenger (Harpin protein): Stimulates plant's own defense responses

Apply both. Avoid copper fungicides (EPA skull-and-bones warning). Don't fertilize—stressed tissue is more vulnerable.

Why Annuals Are Vulnerable

Greenhouse-forced annuals have soft, rapid growth—perfect fungal targets. Harden them off gradually.