Occurrence and Control of Phytophthora clavatus

White feather disease is one of the worldwide diseases of orchids. The disease was particularly severe during the rainy season at the turn of the spring and summer, as well as during the autumn rains, mainly affecting the roots and stem base of orchids. At the onset of the disease, a water-stained yellow lesion appeared close to the soil at the base of the orchid leaf, and then quickly spread to the roots. Afterwards, the leaves were wilting and the stalks were rotted brown and easily broken. In severe cases, orchid pseudobulbs can also be infested, producing white silky mycelium in the diseased area, extending radially and spreading on the surface of the rhizosphere. At the late stage of disease, mycelium is often interwoven to form white at first, and then gradually changes to yellow, eventually showing brown round, rapeseed sclerotia. This is the most typical symptom of the disease that distinguishes it from other diseases. Phytophthora orchidis survives with mycelium or sclerotia in diseased plant debris and potted soil. Sclerotium is extremely resistant to adverse environmental conditions and can survive in pots and soils for 4-5 years, and is transmitted through infected seedlings, diseased soils, and flowing water. After the sclerotium germinates as a mycelium, it can spread across the soil and directly invade or invade from the wound after contact with the blue plant. The sclerotia is heavier in high temperature and high humidity season or conditions, otherwise the disease is lighter. Prevention and control methods Orchid white feather disease, should take comprehensive measures to prevent the main, integrated prevention and control: First, strict selection of disease-free seedlings, flower pots and soil before exposure to high temperature sterilization, or disinfection with lime water; The mature loose and fertile humus soil is used as nutrient soil. The third is that before the orchid seedlings are planted, the soil is treated once again with 30% of the soil bacteria water-removing agent 1000 times. The fourth is that the flower pots should not be placed too densely to facilitate the cultivation. Inter-plant ventilation and light transmission, promote the growth of robust seedlings; Fifth, pay attention to water management, watering should follow the principle of “do not do not pour, pour is poured”, keep the basin soil moist and not wet. In the rainy season, special attention should be paid to the cultivation of shelter from the rain to prevent the rain from splashing directly on the blue seedlings. This is one of the important measures to prevent the occurrence of the disease. The sixth is in the season of high temperature, high humidity, and daylight sickness. A broad-spectrum fungicide thiophanate-methyl sulfate spray 800 times, can play a good role in prevention; Seven is the incidence of orchid seedlings, should grab the disease in time when the timely removal of diseased leaves, spray 500 times "Jinggangmycin" agent, or 600 times the "Tian An" agent, or 500 times the "multi-* well" suspension, or 600 - 800 times the "chlorothalonil" WP, every 7 days Once in 10 days, spray 2 - 3 times. The diseased plants must be promptly removed and centrally destroyed to prevent the disease from spreading. According to another test, the blue seedlings that have been infected with white peony disease are picked up to wash away the soil. The leaves are soaked with 1.5% edible alkali for 1 minute, then the base is soaked for 20 minutes, then washed with clean water, and dried in the shade for 12 hours. Replanting into a new pot colonization has a good therapeutic effect on the white spot disease of orchids. Interested parties may wish to try.

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