Symptoms and control countermeasures of orchid anthracnose

The pathogen of orchid anthracnose mainly harms the leaves and fruits of orchids. At the initial stage, the damaged leaves appeared yellow-brown slightly sunken spots, and gradually expanded into dark brown round or semicircular spots. If the pathogen invades from the leaf edge, the disease spot is mostly semicircular or irregular; if it occurs from the leaf tip, the disease spot extends downward and withered, and the dead part can reach the leaf 1, 5, 3, and 5; if it is damaged from the leaf base, the diseased leaf dries up rapidly, and the serious whole plant dies. In the later stage, the disease spot is dark brown, gray and white in the center, sometimes in the shape of a wheel, with many small black spots, that is, the conidium disk of the pathogen. The size and shape of disease spots vary with different varieties of orchids. The disease spot on Jianlan mostly occurs at the tip of the leaf, which is large and long in shape; the disease spot on Han orchid and hundred-year-old orchid mostly occurs at the leaf edge, and the diameter of the disease spot is more than 20 mm; in the varieties of Heding and Yingchun butterfly around the world, the disease spot is scattered and small, about 1 mm in diameter. The disease spot on the fruit is irregularly long and dark brown. Orchid anthracnose is caused by anthracnose of Colletotrichum, Coelospora, Colletotrichum, Colletotrichum. The conidia of the pathogen are cylindrical and occur in the conidia disk, thus infecting the pathogen. The most suitable temperature for the growth and development of the pathogen is 22 mi 26 degrees Celsius, and the growth stops when the temperature is below 15 degrees Celsius or above 38 degrees Celsius. Colletotrichum gloeosporioides overwintered on diseased leaves or diseased leaves with mycelia and conidia, mainly from wounds and directly in young leaves. Spread by wind and rain, the incubation period is 14 ~ 20 days. The disease can occur from March to November, and the peak period is from April to June. Factors such as high humidity and muggy heat, sunny and rainy weather, poor ventilation, stagnant water in flowerpots, excessive density of plants and serious damage caused by scale insects will aggravate the occurrence and spread of the disease. Almost all orchid varieties are damaged by anthrax in varying degrees. Generally speaking, cymbidium, cold orchid, primrose orchid, cymbidium, cymbidium and Jian orchid are more resistant to disease. Prevention and control measures: 1, remove the diseased body, cut off the diseased leaves and spots in time and burn them in time during the growing season of orchids. 2. Watering or drip irrigation on the edge of the basin to control the leaf humidity and avoid watering at the head, so that water droplets splash to spread pathogen spores. 3. During the onset of the disease, fungicides such as 75% chlorothalonil, 20% tricyclazole, 50% Rebis and 50% Dysen zinc can be sprayed once every 10 seconds for several times in a row, and the effect is better.