Anthracnose is a parasitic disease that is widespread on many plants.
Anthracnose (anthrax from Greek and Latin roots) is a cryptogamic disease. The signs are characterized by the appearance of well-defined round or elongated spots, reddish-brown to black-brown in color, on various organs of the plant. These spots see their centers gradually lighten towards a lighter, white, gray or pinkish color. The tissues dry out, wilt and eventually die during growth. The fungus responsible for the lesions enters the plant and develops there, in wet weather, at around 16-17 ° C minimum. This yeast infection can appear on annual plants as well as on the leaves of trees or on their fruits. The damage is particularly severe on annuals, such as corn and other vegetable plants. Affected trees in their foliage or fruit survive the cryptogamic attack. As described above, the symptoms are comparable from one species to another. It is important to know that each plant is the victim of a specific fungus, which belongs to many genera of pest fungi, of which Colletotrichum and Gloeosporium are perhaps the most frequent. Anthracnose parasites are kept in the soil in winter, in the form of organs called sclerotia, fixed on plant debris. The spores, whose contaminating role is essential, also remain in the winter on dead leaves, in the interstices of the bark ... Sometimes the seeds have been contaminated since the previous harvest, hence their difficulty in emergence (melting of seedlings) .
Plants susceptible to anthracnose
Among the field crops, we can mention alfalfa, corn, flax, and among vegetable plants, beans, peas, tomatoes, melons, lettuce ... In trees and shrubs, walnut, hazel, almond, cherry, plane, raspberry, currant, rose, not to mention the vine, are also affected.
Prevention and control
Severe preventive measures must accompany crops. The parasitic fungus keeps for several years in the soil, hence the need to practice long rotations of sensitive plants (5 to 6 years). Also choose seeds for varieties recognized as more resistant, or seeds previously treated with fungicides. Knowing that the contamination is done mainly by the propagation of spores, which favor the wind, the rain, the runoff, the small animals, it is also necessary to avoid during the vegetation, in wet period, all unnecessary contact like friction by the walking or handling cultivation tools. Avoid excess fertilization favoring the development of tender and vulnerable young shoots. Ensure good ventilation, respect the correct planting distances. If in spite of everything the parasitic attack occurs, quickly tear off the affected subjects and burn them to limit contamination. A preventive biological control is possible by a decoction based on horsetail or garlic, or with comfrey or nettle manure, sprayed every two weeks. Chemical control is carried out using simple fungicides, such as mancozeb for example. We also recommend the preventive use of copper sulphate, Bordeaux broth. But all this before the symptoms appear, the curative treatment being illusory. By C. Schutz-Croué