Language English Botrytis blight. Photo: IRIIS Phytoprotection (C. Malenfant - MAPAQ) OngletsDescriptionSummary The fungus responsible for botrytis blight or grey mould grows quickly in cool, damp weather. The infection may appear on almost all plant species, on both dead tissues and living parts. The first sign of the disease is a greyish downy substance, after which the infected parts dry out or rot. The disease frequently strikes greenhouses, fruit and vegetable warehouses and nurseries. Signs and symptoms The fungus first attacks weakened, injured or dead plant parts before spreading to healthy parts, especially the tender parts of young leaves, flowers and fruit; lower foliage is often more vulnerable. The damage may appear slightly different on different hosts, but the infection usually causes affected parts to gradually dry out or rot. At first, leaves are spotted with irregular water-logged lesions. Later, the lesions become brittle and are sometimes ringed with a paler band of dark concentric circles. In cool, damp weather, infected tissues are covered with thick greyish down. At an advanced stage, the leaves, flower buds and flowers dry out and drop, fruit fall off or rot, and cankers surround stems, causing them to dry out and die. A thick whitish, weblike mat may form on the ground and potting soil. Latin name (genus)Botrytis cinereaHost plants The fungus has no specific host. It can infect most plant species (deciduous and coniferous) and almost all plant parts (leaves, flowers, fruit and stems), regardless of whether the tissues are dead or living. Development cycleDescription and life cycle Botrytis cinerea is a microscopic fungus belonging to the Deuteromycetes family, imperfect fungi, which have no known sexual form. It produces greyish thread-like chains of mycelia. Depending on the climate, it also forms conidia, asexual spores, and sclerotia, compact masses of mycelia that are able to survive in the soil for several years. The fungus survives the winter and dry spells in the form of mycelia, on plant litter, or of sclerotia. As soon as the weather warms up, the overwintering mycelia become active and the sclerotia germinate, forming more mycelia. The pathogen is spread by the wind and rain to new tissues. This is the primary infection period. During cool, damp weather in the growing season, the mature mycelia produce large quantities of fructifications and spores that quickly form a thick greyish down. The spores are dispersed and quickly form fructifications, causing secondary infections, as long as weather conditions remain favourable. The fungus becomes inactive with the first frost in fall. Prevention and controlFavourable conditions The fungus is able to grow at temperatures of 1 to 28°C, but spreads faster in damp, cool weather (12 to 20°C). Other factors may also promote the disease, including a lack of light and air circulation, over-watering or fertilizing, poor soil drainage, drastic pruning, injuries to plants and infected plant litter left lying on the ground. Identification Keep a close eye on your plants for any suspicious spots or grey mould, especially during favourable weather and when plants are weakened by poor growing conditions. Prevention Choose an appropriate site and maintain adequate spacing between plants. Keep plants vigorous by fertilizing them properly and watering them during dry spells. It is best to water early in the day and to avoid wetting the foliage. To allow air to circulate and sunlight to penetrate, prune plants that are too bushy. Divide crowded perennials. Avoid heavy feeding with high-nitrogen fertilizers and drastic pruning, both of which promote the growth of vulnerable, tender shoots. Keep the garden free of plant litter; remove dead leaves and faded blooms from plants. Physical control Cut off and dispose of affected parts; destroy severely affected plants. Regularly disinfect tools with a 70% isopropyl (rubbing) alcohol solution. Never compost infected plant litter. Biological control None available Chemical control In case of a serious infection in the previous year or years, as a preventive measure, apply a low-impact pesticide with QST 713 strain of Bacillus subtilis as the active ingredient. Read the product label carefully and follow the manufacturer's recommendations.