Ascochytosis is a disease of certain cultivated plants, due to one or more fungi with partitioned mycelium, of the family of Deuteromycetes (imperfect fungi) of the genus Ascochyta mainly. This disease is sometimes also called anthracnose, depending on the fungus and plant involved (in the case of peas, for example).
Description of ascochytosis
Ascochytosis can manifest itself on all the aerial organs of the plants concerned (stems, petioles and leaves, flowers and fruits). The first signs are characterized by the appearance of clearly visible spots, such as "cigarette burns", initially round, with blackish contours with a grayish center. You can fairly quickly spot flecks, corresponding to pycnidia, asexual fruiting bodies of the offending fungus. The lesions become larger then necrotize, causing defoliation of the plant, breakage of stems or even deterioration on flowers, fruits or seeds, making them unfit for consumption.
Biology of ascochytosis
The various pathogens responsible for ascochytosis are preserved in the soil, during the winter, on crop debris, and this probably for several years. They are also present in seeds if the pods have been contaminated (in the case of legumes) or on cuttings, in the case of the multiplication of parasitized chrysanthemums for example. The favorable factors for the development of the disease are high humidity and a temperature above 15 ° C. In the spring, the asexual pycnidia or fruiting bodies release a kind of jelly containing the spores. Dissemination takes place nearby and mainly by rain-related splashes. Under certain conditions, sexual fruiting bodies (perithecia) appear, producing spores capable of being transported by the wind, thus widening the area of contamination. Several cycles of contamination can occur during the year, the first being the most damaging.
Plants susceptible to ascochytosis
Among the field plants, one can cite alfalfa, faba beans, lentils, tobacco, wheat, barley, and among vegetable plants, peas and artichokes. In crops of flowering plants, the disease is found, among others, on chrysanthemums, hydrangeas and lilacs.
Prevention and control
Good cultural practices will eliminate as many pathogens as possible. Here are the main recommendations: - quickly destroy the debris at the end of the culture, - use healthy seeds, and possibly previously treated, - reduce the density of the seedlings, - take care to take cuttings from unemerged mother plants, - use substrate " new "when possible, - water at the base of the crops rather than by sprinkling. In case of attack by fungi, a copper-based preparation, for example Bordeaux mixture, will be sprayed. By C. Schutz Croué