White silk disease of orchid

Symptoms of white silk disease, also known as white silk disease, Sclerotinia sclerotiorum. The disease begins from the stem of the orchid plant near the ground, showing flowing water spots from yellow to light brown at first, then browns to black brown rot, spreads on the surface of the rhizosphere soil and the base of the stem, destroys the stem and infects the young leaves and roots, and the leaf sheath and roots produce white hyphae. The injured part was waterlogged, decayed and softened, blackened, until the leaves withered, the bacteria spread to the pseudobulb, the sclerotia changed from white to reddish brown to brown necrosis, and in severe cases, the whole plant withered.

The pathogen and the characteristics of the disease are semi-known subphylum fungi. The pathogen overwintered as sclerotia in soil or fertilizer and on undecayed remains, and the hyphae could also overwintered on undecayed remains in areas with high winter temperature. the sclerotia germinated the following year, spread in the soil and invaded from the base of orchid leaves. Bacteria check has strong resistance to adverse environment and can survive in the soil for several years. It can be spread by running water, irrigation water, Rain Water sputtering and fertilization. The soil is sour and the disease is the most serious, and the disease is easy to be induced in high temperature and humid weather. The infection began from April to May, and the disease occurred rapidly during the peak period from June to August, resulting in the rot and death of the injured orchid plants.

Prevention and cure measures

1. Changing the pH of the matrix of orchid, the disease is easy to occur when the matrix is partial to acid (pH < 5.3). Therefore, mixing plant ash with a volume ratio of 10 in the substrate, or pouring 0.3% limewater to increase the pH value to about 6.5, can reduce the occurrence of white silk disease, and the effect is obvious.

2. Soil disinfection, the matrix soil is sterilized with 0.2% pentachloronitrobenzene 500 times solution and 50% carbendazim wettable powder 600 times solution, or the rhizosphere and soil can be sprayed with pentachloronitrobenzene 500 times solution or 70% methyl thiophanate 800 times solution, or 50 grams of pentachloronitrobenzene powder mixed with 4 to 5 kilograms of semi-dry and wet fine sand, sprinkled on the rhizome of diseased plants, can inhibit the spread of the disease.

3. Spread fresh plant ash to prevent, in the rainy season from May to June in the south, the soil moisture is high, and white silk disease is easy to occur on the basin surface. We should quickly move out of the orchid field to "isolate", remove the matrix infected with mycelium, cut off the diseased root, spray 1000 times of potassium permanganate solution for disinfection, or use 1500 times of methyl topiramate to spray roots and wounds, and sprinkle fresh plant ash around the orchid root. Then covered with matrix root protection, 2 to 3 days before watering, if the substrate wet can be delayed for 5 to 7 days, the control effect is good.

4. When the disease occurs, 2000 times aqueous solution of medical chloramphenicol injection is used to sprinkle the diseased plants once a day for 3 times. Once the disease occurs, the diseased leaves should be cut off, the ventilation conditions should be improved, and the whole orchid should be soaked in 10% copper sulfate solution for disinfection. To the nearby orchid plant, also want to spray comprehensively, wet the base, basin surface, spray once a day, apply twice in succession, can control the disease, the control effect is good.

5. After the new buds grow out of the soil, 0.05% chloramphenicol is sprayed once a week for 2 to 3 times. If the basin soil is dry, this medicine can be used to prevent bacterial infection. It can also be sprayed with 1500 times aspirin solution, which can enhance the immunity of the orchid plant and prevent the invasion and spread of bacteria.

6. in the period of new bud extension and leaf expansion, medical penicillin, streptomycin, chloramphenicol or penicillin can be diluted to 2000 times, sprinkle the diseased plant, and spray comprehensively, once every 3 to 4 days, twice in succession, the control effect is good.

7. Spray 50% benzoate wettable powder 1000 times, or 50% carbendazim wettable powder 500 times, or 50% thiophanate wettable powder 500 times or 70% chlorothalonil wettable powder 1000 times, every 7 to 10 days, spray 2 to 3 times, the control effect is good. It can also be sprayed before and after overcast rain or before and after rain. 50% Sukeling powder 500 times, or 50% Nongliling (ethylene sclerotiorum) powder 500 times, disinfectant alum 500 to 600 times, 5% Jinggangmycin water agent 300 times, spraying stem, leaf, basin surface, the control effect is remarkable.