Anthracnose

Anthracnose is caused by several fungal species in the genus Colletotrichum, along with a few related fungi grouped under the same common name. On affected plants you'll see dark brown to black, sunken lesions on leaves, stems, flowers or fruit. Within these lesions, especially in humid weather, tiny raised black fruiting bodies appear, often oozing pink, orange or cream spore masses in concentric rings. On fruit such as mango, avocado and pawpaw, lesions start as small dark spots that enlarge and sink as fruit ripens. On lawns, the disease shows as irregular patches of thinning, yellow to reddish-brown turf, with tiny black spore-producing structures (acervuli) visible at the base of the grass blades under close inspection.

Anthracnose affects a very wide range of hosts across Australian home gardens, including vegetables (beans, cucurbits, brassicas, lettuce, onion), fruit trees (mango, avocado, pawpaw, guava, olives), ornamentals (violets, roses), grapevines and berries, and turf grasses such as couch and kikuyu.

The disease is most active during warm, wet or humid conditions, typically spring through to autumn in most of Australia, and tropical/subtropical regions can see it year-round. Spores spread by splashing rain or irrigation water, on tools, and on infected plant debris or seed. Extended leaf wetness and poor air movement favour infection.

Management relies on reducing humidity and leaf wetness around plants: improve airflow through spacing and pruning, water at the base rather than overhead, and avoid watering late in the day. Remove and dispose of infected leaves, fruit and prunings rather than composting them, and practise crop rotation for vegetables. In turf, avoid drought stress and excess nitrogen, and maintain a balanced fertility and mowing program, as anthracnose often follows plant stress.