Anthracnose of Orchid and its Control

Anthracnose occurs in all areas where orchids are cultivated in China, especially in Tianjin, Shanghai, Nanjing, Guangzhou, Chengdu, Lianyungang and Xi'an. When the disease is serious, it not only affects the normal growth of orchids, but also leads to the death of whole leaves. Anthracnose not only harms Cymbidium, Jian Orchid, Hanlan and other orchids (that is, Chinese orchids, orchids for short), but also epiphytic orchids such as tiger orchids and broad-leaf orchids, as well as Guangdong evergreen, violets, marigolds, mulberry, sweet-scented osmanthus and other flowers.

First, symptom characteristics.

Anthracnose mainly harms the leaves of orchids and sometimes infects stems and fruits. The disease spot on the leaf begins to be round or oval, the center is light brown or grayish white, the edge is dark brown or dark brown, and there is a greenish halo around it; black spots are produced on the disease spot in the later stage, scattered or slightly arranged in a wheel, and orange-yellow sticky matter will appear under wet conditions. With the development of the disease, the disease spot on the leaf can expand into irregular spots up to several centimeters long, or the disease spot can be connected into a piece, and finally cause the leaves to wither and yellow. The size of the disease spot on the leaf is 3-20 mm, which varies greatly. Irregular or striped black-brown spots appeared when the stems and fruits were damaged.

Second, the law of the disease.

The disease is caused by several kinds of anthrax fungi (Orchidaceae, Cymbidium and Colletotrichum gloeosporioides). The pathogen overwinters on diseased leaves, diseased leaf residues and withered leaf bracts, and spreads by wind, rain and insects under suitable climatic conditions the following year; invades the plant mainly through various wounds. The disease can occur almost all the year round, but it is serious in summer and autumn. Such as the southern plum rain season, or autumn typhoon accompanied by heavy rain, so that orchid leaves injured, or high humidity and muggy heat, placed too dense, poor ventilation, stagnant water in the basin, the disease is the most serious. Watering from the top of the plant is easy to spread the disease. Because the roots of orchids propagated in that year are easily damaged, the disease is often serious. The heavy consolidation of basin soil will also aggravate the disease.

Third, prevention and control methods.

1. Strengthen cultivation management: greenhouse should be ventilated and transparent. In winter and early spring of the following year, special attention should be paid to keeping warm so that it will not suffer frost and frost damage, so as to enhance its ability to resist diseases. After moving outside, it should be placed in the shade shed to prevent the attack of wind and rain, at the same time, there should be enough sunlight in the shed, and it is better to pour it slowly from the edge of the flowerpot or soak in the basin to irrigate, so as to reduce the spread of bacteria with water droplets caused by pouring above. Flowerpots should not be placed too tight. Orchid fertilization should pay attention to science. As we all know, orchids should be ripe rather than grown. Anthrax can easily be induced by the application of raw fertilizer. When potted, new soil should be replaced.

2. remove the source of infection: remove the diseased leaves and their remains in time, especially before entering the house in winter, burn or bury the diseased leaves on the plant and the remains in the basin thoroughly, so as to eliminate the source of infection and prevent the spread of the disease. In winter and spring, 0.5-1% Bordeaux solution was sprayed on the ground, basin and plant for 1-2 times.

3, chemical control: before the onset of the disease, 0.5-1% Bordeaux solution or 65% Dyson zinc wettable powder 600-800 times, sprayed every 7-10 days, has a better protective effect. During the onset of the disease, 50% carbendazim 800x solution or 75% methyl topiramate 1000-fold solution can control the spread of the disease.

4. Non-pesticide prevention and treatment: ⑴ vinegar. Spraying vinegar on the leaves of orchids can prevent anthracnose. Pour 1 tablespoon of vinegar into 1 kg of water and spray the orchid plant. Vinegar can also be added when using pesticides. ⑵ leek juice. The anthracnose can be treated by mixing leek juice and clear water at the ratio of 1:60 and spraying orchid plants twice a day for several days. ⑶ pig bitter bile. Anthracnose and soft rot can be controlled by mixing pig bitter bile and clear water at the ratio of 1 to 100, adding a small amount of washing powder and spraying orchid plant. ⑷ quicklime aqueous solution. First, the quicklime was weathered into powder with appropriate amount of water, then the weathered quicklime powder and clear water were put into the container at the proportion of 1:60, and the clarification solution was sprayed around the orchid plant to control anthracnose. Quicklime is alkaline and can also prevent and cure white silk disease of orchids.