Anthracnose Leaf Spot Fungus -- Harvest to Table

Anthracnose—also called leaf spot fungus–is a catch-all name to describe several diseases caused by fungi that flourish in wet weather.

Anthracnose causes small, dark spots with yellow halos to develop on leaves. The spots become sunken lesions. Lesions may also form on stems and fruits. Leaf spots grow larger, become angular, and then dry until the centers of the spots fall out leaving holes in the leaves. Infected leaves often drop prematurely. Spore masses that look like pink slime may ooze from the lesions. Diseased stems and twigs die back.

Disease range: Eastern and Central United States, southeastern Canada, seldom seen in arid climates.

Scientific name: Colletotrichum spp., Gloeosporium spp.

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Anthracnose lef spot target plants

Plants that can be attacked by anthracnose leaf spot include beans, cucumber, peppers, potatoes, melons, tomatoes, watermelons, gourds (usually not a problem on peas, squash, or pumpkin), and bramble fruits. Trees: dogwood, ash, elm, maple, oak, sycamore, and other trees.

Anthracnose leaf spot damage

Beans

Bean leaves develop dark red or black spots on the undersides; spots are often elongated dark brown and may follow veins. Spots may appear on the upper surface of leaves.
Bean pods develop spots or lesions that may be filled with pink masses of spores. Seeds in pods may have dark spots.

Chinese cabbage

Chinese cabbage leaves develop small, round gray spots on leaves; elongated spots develop on stems.

Cucumbers

Cucumber leaves develop yellow, water-soaked spots on leaves; the spots turn brown
Cucumber stems may develop pink, jelly-like lesions; when stems are affected plants may drop leaves.
Cucumber fruits develop dark, sunken areas with pink spores.

Lettuce

Lettuce leaves develop small, round gray spots; elongated spots develop on stems.

Melons

Melon leaves develop light brown spots that turn to reddish brown on muskmelons and black on watermelons. Spots enlarge. The leaf may shrivel and die.
Melon stems develop water-soaked and elongated; leaf stems become sunken and brown.
Melon and cucumber fruits develop dark, sunken lesions.

Peppers

Pepper fruits develop small, circular, water-soaked spots as fruit approaches maturity; as spots darken and deepen they develop concentric circles; in warm weather, the spots soon penetrate and spoil the fruit.

Potatoes

Potato stems develop lesions just below the soil surface.
Potato tubers develop black dots on the skin.

Radishes

Radishes develop small, round gray spots on leaves; elongated spots develop on stems.

Raspberries

Raspberries (black) purplish circular sunken spots develop on lower canes; spot centers turn gray; berries ripen unevenly.

Rhubarb

Rhubarb stems and petioles develop water-soaked spots

Strawberries

Strawberry stems girdle before they can root.

Tomatoes

Tomato fruits develop tan spots that become dark depressed spots; concentric rings are often visible in the spots.
Tomatoes fruits develop small, circular, water-soaked spots as fruit approaches maturity; as spots darken and deepen, they develop concentric circles; in warm weather, the spots soon penetrate and spoil the fruit.

Turnips

Turnips develop small, round gray spots on leaves; elongated spots develop on stems.

How Anthracnose spreads

Fungi spores are spread by wind, rain, insects, and gardeners handling wet plants. Spores can enter plants through wounds or through leaves when plants are wet. Spores may also be carried in infected seeds. Spores germinate only in a water film. Spores grow at temperatures between 59°-77°F.

Anthracnose life cycle

Fungi overwinter as mycelium in seed and in garden debris. Spores formed in the spring are splashed on host plants where they germinate. Ne fungi form a peg at the end of the hyphae which can mechanically invade plant tissue.

Anthracnose organic controls and prevention

Wetness encourages Anthracnose fungi. Here are ways to control or prevent Anthracnose:

Grow resistant varieties. Use certified disease-free seed grown in the western United States.
Avoid overhead irrigation. Avoid wetting foliage.
Grow crops on trellises or poles to encourage good air circulation.
Mulch around plants to decrease splashing from rain or sprinkler irrigation.
Trim overhead trees or shrubs to increase sunlight to sun-loving plants.
Avoid working among wet plants.
Prune out infected branches or twigs.
Remove infected plants from the garden.
Burn or dispose of diseased plants.

Anthracnose non-organic controls

Fungicides include lime sulfur, Bordeaux mixture, and chlorothalonil. These fungicides may be harmful and toxic to humans, animals, beneficial insects, bees, and aquatic animals when not applied properly. Consult your cooperative extension for application information.