ANTHRACNOSE CONTROLAnthracnose is a general term for a variety of different plant diseases, characterized by common appearance of dark tissue spots on stems, leaves or fruit. This disease is caused by a large variety of organisms, including fungi, bacteria, mycoplasmas and viruses.
HOST PLANTS: Common in many different types of plants. Apples, Butternut Squash, Grapes, Mulberries, Roses, Elm, and Oak are especially susceptible.
SYMPTOMS: Anthracnose symptoms vary with the host plant, weather, and time of year infection occurs. This disease develops on shoots and expanding leaves. Small tan, brown, black, or tarlike lesions appear on infected leaves of hosts. Dead leaf areas may be more irregular on other hosts such as ash. Sycamore anthracnose lesions commonly develop along the major leaf veins. If leaves are very young when infected, they may become curled and distorted with only a portion of each leaf dying.
Generally, mature leaves are resistant to infection, but when conditions are favorable, they may become spotted with lesions. Heavily infected leaves fall prematurely throughout the growing season, and sometimes trees are completely defoliated. Early leaf drop is usually followed by production of more leaves. Twigs and branches also may be attacked and killed, resulting in a tree with crooked branches.
On some trees, cankers (infected areas that may or may not be surrounded by callus tissue) are another symptom of anthracnose infection. Cankers develop on twigs, branches, and the trunk, occasionally resulting in girdling and dieback. If defoliation, branch dieback, or cankering does not occur every year, anthracnose will not seriously harm plants. In California, anthracnose rarely causes permanent damage to plants except for elm trees.
FAVORED ENVIRONMENT: Anthracnose overwinters in and on soil, seeds and garden waste. Cool moist weather promotes its development, and the optimum temperature for continued growth of the spores is between 75-85 degrees F. Moisture is required for development and germination of the fungus as well as for infection of the plant. It is spread by wind, rain, insects, and garden tools.
ANTHRACNOSE CONTROL: Choose resistant plant varieties when possible and use western grown seeds, which have not been exposed to the disease. If anthracnose is a common problem, do not save your own seed from plantings. To avoid spreading the disease, keep out of gardens when plants are wet and make sure to disinfect all garden tools (one part bleach to 4 parts water) after use. Do not compost infected leaves, fruit, or stems and thoroughly clean up garden areas in the fall, after harvest, to reduce over wintering sites for the fungal spores.
Sulfur or copper powders/sprays should be applied weekly to infected plants starting when the disease is first noticed and continuing throughout the growing season. These organic fungicides will not kill the disease, but prevent the spores from germinating. Seeds may also be treated prior to planting.