Anthracnose

Colletotrichum spp. and allied anthracnose pathogens

Anthracnose is an umbrella name for numerous host-specific diseases caused mainly by Colletotrichum species complexes and, on some woody hosts, other fungi historically called anthracnose pathogens. Depending on the host, disease may appear as leaf spots, shoot blight, cankers, blossom blight, fruit rot, or latent postharvest decay. A single generic diagnosis is insufficient for management because strawberry crown rot, mango anthracnose, sycamore anthracnose, bean anthracnose, and apple bitter rot have different biology and controls. The record should guide triage until the host and pathogen are resolved. Warm wet weather favors many Colletotrichum diseases, while some tree anthracnoses are most severe in cool wet springs.

Identification

Begin with exact host identity, tissue affected, and timing. Colletotrichum diseases may show dark sunken lesions, orange or salmon spore masses, black acervuli, setae, or concentric fruit rot. Tree anthracnoses can produce vein-associated leaf necrosis, twig dieback, and cankers without orange spores. Collect fresh lesion margins, symptomatic fruit, stems or crowns as appropriate, plus healthy comparison tissue. Laboratory diagnosis may combine microscopy, isolation, and multilocus sequencing because morphology and ITS sequencing alone often cannot resolve species complexes. Do not infer host range or fungicide sensitivity from the word anthracnose. Differentiate from Botrytis, Alternaria, bacterial blights, sunscald, chilling injury, and other fruit rots.

Symptoms / Signs

Expression varies by pathosystem. Leaves may develop irregular tan to black spots or necrosis following veins. Stems and petioles can carry dark sunken lesions that girdle shoots. Flowers may blight before fruit set. Fruit lesions are often circular, sunken, and dark, with orange, pink, or cream spore masses under humidity; latent infections may remain invisible until ripening. Crown infections can cause sudden wilt without conspicuous foliar spots. The host and infected organ therefore belong in every diagnosis.

Life Cycle / Process

Many Colletotrichum species survive in infected perennial tissue, mummified fruit, crop debris, seed, transplants, or asymptomatic host tissue. Conidia spread mainly by splash and handling, while some species produce wind-dispersed sexual spores. Infection may be quiescent until tissue ripens or becomes stressed. Temperature and wetness optima differ. Woody-host anthracnose fungi may overwinter in twigs and attack new growth during cool rains, whereas tropical fruit anthracnoses intensify in warm humidity.

Prevention

Replace the umbrella diagnosis with a host-specific record whenever possible. Start with tested seed, certified transplants, and clean propagation stock. Remove mummies and infected debris, prune diseased twigs in dry weather, reduce splash, and shorten wetness duration. Protect fruit from wounds and cool harvested produce promptly using host-appropriate conditions. Select resistant cultivars where validated. Preventive fungicide timing must follow the particular crop and pathogen; a generic anthracnose spray program is scientifically unsafe.

Management / Control

Quarantine high-value propagation lots until the affected organ and pathogen complex are identified. Remove severely infected plants, fruit, or twigs without scattering spores. Improve ventilation and irrigation practices. Submit samples before applying broad-spectrum fungicides, since treatment can suppress diagnostic signs and different Colletotrichum populations may be resistant to different FRAC groups. Once identified, follow the canonical host-specific disease record and current local crop recommendations. Existing necrosis cannot be cured; management protects new growth and prevents postharvest spread.

Procedure Steps

1. Identify host, cultivar, tissue, production stage, and whether symptoms appeared before or after harvest. 2. Photograph lesion margins and any orange, salmon, or black fruiting structures under humid conditions. 3. Collect active margins and the relevant whole organ, keeping fruit or crowns cool but not waterlogged. 4. Request host-specific laboratory identification and differentiation from Botrytis, Alternaria, bacterial disease, and abiotic injury. 5. Move the case to a canonical host-specific record and implement its sanitation, cultural, and resistance-management actions.

Safety Notes

Most plant-pathogenic anthracnose fungi are not routine human pathogens, but moldy fruit and spore-laden debris can irritate susceptible workers. Wear gloves, avoid aerosolizing dry cultures, and follow food-safety disposal rules. Observe crop labels, preharvest intervals, and reentry restrictions.