Anthracnose identification & organic treatment
Colletotrichum spp.
How to identify anthracnose
A group of closely related fungi that cause sunken, water-soaked spots on ripening fruit and dark blotches on leaves and stems. Especially damaging on cucurbits, peppers, beans, and tomatoes right at harvest time.
Symptoms
- Small water-soaked spots on leaves that enlarge into tan-to-brown dead patches, often angular along veins
- Sunken, circular, dark spots on fruit that develop pink-orange spore masses in humid weather
- Cankers on stems and vines that can girdle and collapse them
- Fruit rot often shows up post-harvest, after fruit looked fine in the field
Host crops
Cucumber, Winter squash, Pumpkin, Pepper, Tomato, Bush bean, Watermelon.
How it spreads
Overwinters in seed, crop debris, and volunteer plants; spread by splashing water, contaminated seed, and handling wet foliage.
Favorable conditions
Warm, wet weather (75-85°F) with extended leaf wetness; worse under overhead irrigation and in fields with poor drainage.
Progression
- Leaf infection (Early-mid season, wet spells) — Small lesions expand along veins.
- Vine/stem cankers (Mid season) — Sunken cankers can girdle stems.
- Fruit rot (Near/at ripening) — Sunken spots with pink spore ooze in humidity; spreads in storage.
Organic treatment for anthracnose
- 1. Remove and destroy infected fruit and vines · low effort
Pull affected fruit and prune infected vine sections as soon as seen; do not compost.
When: Ongoing
- 2. Copper fungicide · medium effort
Apply OMRI-listed copper every 7-10 days starting when weather turns warm and wet, especially as fruit begins to size up.
When: Preventively through fruiting
- 3. Avoid working wet plants · low effort
Stay out of the patch when foliage is wet to avoid spreading spores on hands and clothing.
When: All season
Prevention
- Use certified disease-free seed; anthracnose travels readily on seed.
- Rotate out of susceptible crops for 2 years.
- Drip irrigation instead of overhead sprinklers.
- Harvest promptly and handle fruit gently to avoid wounds that invite rot.
Easy to confuse with
- Gummy stem blight
- Bacterial spot
- Blossom end rot (on fruit, but no fungal ooze)
Terms on this page
- Spores / sporulation
- Spores are a pathogen's seeds. Sporulation is when it starts producing them, often as fuzz or powder you can see.
Sources
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