Anthracnose, also called bird’s-eye spot, is a disease caused by several similar species of fungus. These fungi affect many plants:
- Snap beans.
- Shade trees, particularly sycamore and ash.
Athracnose development is favored by wet conditions and temperatures between 75°F and 85°F. It spends the winter in dead plant matter and is spread by rain, wind, insects, and garden tools. Wounds left in plant tissue by insect pests provide the entry points.
Not surprisingly, stressed plants are more vulnerable to anthracnose than healthy plants. Stress caused by poor soil drainage is particularly problematic.
- Distorted leaves.
- Dark, sunken, water-soaked spots on leaves, stems, and fruits.
- Small, shrunken, dry spots on turnips.
- Spots with raised borders and sunken centers on bean pods.
- Black bean seeds.
- Small purple spots with light-colored centers on leaves.
- “Shotgun” holes in leaves.
- Round, sunken pits in canes.
- Split bark.
- Dry, seedy fruit.
- Winter die-back.
- Withered, blackened young leaves.
- Brown areas along veins of older leaves.
- Bud, shoot, and twig blight on sycamore trees.
- Leaf drop.
- Dark mats on lower leaf sheaths.
- Dead, black crowns.
- Irregular patches of dead turf, changing from reddish-brown to tan.
Treatment is not worthwhile in vegetables. Discard infected plants, preferably in the dumpster versus the compost pile. Do not save seeds from diseased plants.
In Kansas, fungicides to treat trees and brambles are usually unnecessary since the disease frequently runs its course with little permanent damage. However, sanitary measures, such as destroying fallen leaves and pruning out diseased tissue can be beneficial. When pruning plants affected with anthracnose, disinfect tools with bleach before using them on healthy plants.
Turfgrass is usually treated with fungicide. Steps must also be taken to reduce the stress on the turf (see below).
Keeping your plants healthy is the best way to prevent anthracnose:
- Check the light requirements of each plant.
- Practice crop rotations in your garden; do not plant vegetables that share diseases in the same place two years in a row.
- Test the soil to ensure that nutrients are in balance.
- Keep plants well watered, but ensure that the soil drains well.
- Never work with your plants when they are wet.
- Avoid using an overhead sprinkler system.
- Keep produce from coming into direct contact with moisture.
- Provide plants with support to keep fruit off of the ground.
- Prune plants as necessary to allow proper airflow.
- At the end of the season, remove dead plant matter that fungi could hide in over the winter.
If in spite of your efforts anthracnose is a recurring problem in your garden, consider purchasing plant varieties with genetic resistance to the disease.