Anthracnose
Also known as Colletotrichum, Discula
In short
Anthracnose is a name for a group of fungal diseases, caused by various species that each usually attack particular hosts, that produce dark dead lesions on leaves, stems and fruit. The spores are spread by splashing water, so the disease needs wet conditions and cannot spread in dry weather.
How it looks
Dark, irregular dead lesions on leaves; on some trees, such as sycamore and oak, they run along the main veins. On houseplants, leaf tips often discolour progressively from yellow to tan to dark brown. On bean pods, lesions can be large brick-red to brown blotches.
Signs
Leaf spots and blotches, premature leaf drop and, on woody plants in severe cases, damage to twigs and branches.
Life cycle
The fungi survive on infected leaves, twigs and debris. In wet weather they release spores that are spread by splashing rain or irrigation water onto new growth.
What favours it
Prolonged wet weather after new growth appears, irrigation or misting that wets the foliage, and crowded canopies that stay damp.
Prevention
- Water at the base and avoid misting foliage of susceptible plants.
- Space plants and open up dense growth so leaves dry quickly.
- Grow resistant cultivars where available.
- Clear fallen leaves and twigs, which carry the fungus.
Treatment
Start with the first step and move down only if the problem persists.
- Remove and dispose of infected leaves; prune out infected twigs when the plant is dry.
- Keep foliage dry while the plant recovers.
- Fungicides only protect healthy tissue and do not cure existing lesions; copper-based and systemic products are used as protectants. Follow the product label.
Pros and cons
Cons
- Existing lesions cannot be cured, only prevented from spreading to new growth.
- Repeated defoliation weakens woody plants.
Look-alikes
- Fungal leaf spot
- Leaf spots are usually discrete round spots, often with yellow margins or rings; anthracnose tends to form larger, irregular dead blotches or tip dieback.
- Sunburn
- Sunburn appears suddenly on the most exposed leaves and does not spread in wet weather.
- Bacterial leaf spot
- Bacterial spots are often angular, water-soaked and bounded by veins, with yellow halos.
- Salt and fertilizer burn
- Fertiliser burn browns tips and edges of many leaves at once and relates to feeding.
Affected plants
Many trees (ash, dogwood, elm, maple, oak, sycamore, walnut), vegetables such as beans, some flowers and many foliage houseplants.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.