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Gardening glossary

Anthracnose

Anthracnose is not one disease but a family of related fungal infections caused mostly by species in the genus *Colletotrichum* (with related contributions from *Apiognomonia* and *Glomerella*). The shared visual signature — dark, sunken, water-soaked lesions — gives the group its common name (from the Greek *anthrax*, "coal").

What anthracnose looks like:

- **On leaves.** Small dark spots that expand into irregular brown or black blotches, often along veins or leaf margins. Severely infected leaves yellow, curl, and drop. - **On stems.** Sunken, dark, oval lesions; girdled stems wilt above the infection point. - **On fruit.** This is where anthracnose is most damaging. On tomatoes, peppers, apples, mangoes, papayas, and strawberries, you see sunken circular spots that develop concentric rings and, in moist weather, pink or orange spore masses (the "acervuli") in the centre. On beans (Colletotrichum lindemuthianum), brown sunken lesions appear on pods. - **On woody hosts** like ash, dogwood, sycamore, plane trees, and oak — irregular brown blotches along leaf veins and sometimes shoot dieback in spring.

Conditions that favour anthracnose:

- **Prolonged leaf wetness** — 12+ hours of damp foliage. This is the single biggest risk factor. - **Mild temperatures** (18–25 °C) — the optimum range for most Colletotrichum species. - **Splash-dispersed spores** — overhead irrigation, rain, or even careless watering moves spores from sick to healthy tissue. - **Crowded plantings** with poor airflow.

Management for home gardeners:

1. **Resistant varieties.** Especially for beans and tomatoes, choose cultivars listed as resistant. 2. **Clean seed.** Beans in particular can carry anthracnose on the seed coat; buy certified disease-free seed. 3. **Water at the base, not the leaves.** Drip irrigation or soaker hoses, mornings only. 4. **Spacing and pruning** for airflow. 5. **Clean up debris.** Anthracnose overwinters in fallen fruit, infected stems, and leaf litter. Bin (do not compost) anything showing symptoms. 6. **Rotate crops.** A 3–4 year break from the affected family helps. 7. **Copper-based fungicides** (copper oxychloride, copper sulphate) applied preventatively can suppress spread during wet weather. Use according to label, and note that copper accumulates in soil. 8. **Tool hygiene.** Disinfect secateurs with a 10% bleach or 70% alcohol wipe between plants when symptoms are present.

For ornamental trees, severe anthracnose rarely kills mature plants — they leaf out again. Rake up infected leaves in autumn to break the cycle.

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Related terms

Blight

Blight is rapid, widespread browning, withering, and death of plant tissue caused by fungal, oomycete, or bacterial pathogens. Unlike discrete leaf spots, blights collapse large sections of leaf, stem, or flower at once.

Leaf spot

Leaf spot is a general term for discrete, often circular lesions on leaves caused by fungal or bacterial pathogens. Spots may be brown, black, tan, or yellow-haloed and often expand or merge in humid conditions.

Mildew

Mildew is a catch-all term for two distinct fungal-type diseases: powdery mildew (white surface dusting that thrives in dry warm air) and downy mildew (yellow leaf-top patches with grey-purple fuzz beneath in cool wet conditions).

Vascular wilt (verticillium and fusarium)

Vascular wilt diseases are soil-borne fungal infections — most commonly Verticillium and Fusarium species — that invade a plant's xylem and block water transport. Symptoms include sudden one-sided wilting, yellowing leaves, brown streaks inside cut stems, and rapid collapse. There is no cure once infected.

Damping off

Damping off is a soil-borne fungal disease that kills seedlings within days of germination, caused by Pythium, Rhizoctonia, Fusarium, and Phytophthora species. Seedlings collapse at the soil line with a pinched, water-soaked stem. Prevention is the only real cure — by the time you see symptoms, intervention is usually too late.