Plant Problem Diagnostic
Anthracnose (Colletotrichum spp.): Identification and Cultural Management
The short answer
Anthracnose is a group of fungal diseases (mostly Colletotrichum species, plus related fungi on trees) that cause dark, sunken lesions on leaves, fruit, stems, and twigs across a wide range of plants. On vegetables like cucumber, melon, and squash it makes irregular brown leaf spots whose centers may drop out for a ragged look, plus sunken fruit lesions. On shade trees such as sycamore, oak, ash, and maple it causes tan to brown blotches that follow the leaf veins, leaf distortion, and spring leaf drop.
The disease overwinters in infected debris and, for some crops, in seed, and it spreads in wet, splashing conditions. Management is cultural: clean up and destroy infected debris and fallen leaves, improve airflow and light, keep foliage dry, use clean seed and resistant varieties, and rotate vegetable families. Where a fungicide is warranted on chronic problems, use a product labeled for that plant and follow the label; consult Extension for timing.
How to identify it
- Vegetables: irregular brown leaf spots with centers that fall out, plus sunken, dark, sometimes oozing spots on fruit
- Shade trees: tan to brown blotches that follow leaf veins, cupped or curled distorted leaves, and spring leaf drop
- Twig and stem cankers on some woody hosts
- Symptoms worsen after periods of wet weather
Conditions that favor it
- Cool, wet spring weather at leaf-out favors tree anthracnose
- Warm, wet, humid weather with splashing rain or overhead irrigation favors vegetable anthracnose
- Infected plant debris and fallen leaves left in place from the previous season
- Contaminated seed for some crops
Cultural management steps
- 1Sanitize debris — Rake and destroy fallen leaves and remove infected plant residue before winter so the fungus cannot re-infect next season.
- 2Improve airflow and light — Space and prune plants to increase air circulation and light penetration so foliage dries faster.
- 3Keep foliage dry and use clean inputs — Water at the base rather than overhead, and start with disease-free seed and resistant varieties where available.
- 4Rotate vegetable families — Rotate so susceptible crops (for example, cucurbits) are not replanted in the same spot for several years.
When to escalate
Anthracnose on established shade trees is usually cosmetic and rarely kills a healthy tree, so sanitation is often enough. If a young or stressed tree defoliates repeatedly, if a vegetable crop is being ruined, or if you are unsure which leaf-spot disease you have, ask your local Extension office. Any fungicide use should follow the product label for that specific plant.
✔ For most landscape trees, healthy anthracnose leaves that drop are replaced by a new flush; focus on raking up infected leaves rather than spraying a large tree.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Minnesota Extension — Anthracnose of trees and shrubs — Tree symptoms (vein-following blotches, distorted leaves, spring leaf drop), cool wet spring conditions, sanitation of fallen leaves
- University of Minnesota Extension — Anthracnose of cucurbits — Vegetable symptoms (ragged leaf spots, sunken fruit lesions), clean seed, rotation, and resistant cultivars
- NC State Extension — Anthracnose of Cucurbits — Rotate so three years pass before replanting cucurbits; integrated cultural management with resistant cultivars