How to prevent Zinnia black spot
A letter from a reader from Ninghai County, Zhejiang Province asked: After planting potted Zinnia plants from the seedlings to the upper pots, the plants were flowered, and pesticides were sprayed and prevented four times. However, many plants still showed melasma and turned dark brown. Plants sprouting from a small amount of seeds that fell on the edge of the flowerbed had not been watered, fertilized, or sprayed since their growth until flowering. Is this what is the reason? How to prevent its black spot? Answer: Your potted Zinnia has been controlled by multiple sprayings. Black spot disease still occurs. The plants that naturally sprout on the ground are not disease-free and robust without control. This phenomenon may result from the following reasons: Is black spot disease is a kind of more stubborn disease, its leaves, stems, flowers can be victimized, leaves early stage of disease is dark brown spots, and soon expanded into irregular large spots, diameter between 0.2 cm to 1 cm, Reddish-brown, the center becomes grayish white necrosis, but the lesions on the center and edges of the lesion on the dorsal surface are the same. As the spots increase, the whole leaf becomes brown and dry. The onset of the stem begins with the petiole and grows longitudinally into strips of dark brown patches. When wet, a black layer of powdery mildew develops in the affected area. When the stem base of the seedling stage suffers damage, it forms a dark brown to black-brown center with ulceration of the subsidence. When severe, it can cross the base and cause erection. Based on these characteristics, it can be accurately determined whether the plant is infected with melasma. It overwinters with mycelium on damaged stems and leaves. The diseased seeds are also the primary infestation source. In the spring of the following year, conidia spread through wind and rain, invade from wounds or stomata, and occurs severely in high temperature seasons. From August to September, the incidence is high. Period, the plants are too dense, poor ventilation and light transmission, and too much nitrogen fertilizer can easily cause the disease. The second is that the timing and methods of prevention and control are not appropriate. This prevents the occurrence and spread of the disease. The diseased stems, leaves, and flower residues should be promptly removed to centrally burn them. This cannot be ignored. It is important to harvest full kernels on healthy, disease-free plants. Unripe plants growing on the edge of the flowerbed may be germinated and grown from seeds without germs. It may be a single plant that is relatively disease-resistant and may be planted for a test. Once a small number of lesions are found on the plants, the diseased leaves should be rapidly cut and burned. In a timely manner, all plants should be sprayed with 50% agent-zinc and mancozeb WP 500 times, once every 10 days, and continuously for 3 times. Up to 4 times, special attention should be paid when spraying the spray on both sides of the blade. The third is to pay attention to the preparation of potted soil, potted Zinnia soil can not be used in the second year, requiring the use of loose fertile, well-drained, sandy soil rich in humus and organic fertilizer mixed preparation. During the cultivation process, it is necessary to strengthen ventilation and light transmission, control the amount of nitrogen fertilizer, and pay attention to the balanced supply of the three elements of nitrogen, phosphorus and potassium.
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