Canker disease is a domestic and foreign quarantine object for citrus fruit trees, mainly due to the blind transport of fruit and negligence in production. It poses a major threat to base construction, commercialization of pollution-free production and fruit exports. 1. Symptoms and its incidence rules Shatian pomelo canker disease is a bacterial disease that mainly affects the leaves, branches and fruits of navel oranges and produces ulcer lesions. The leaves of the victim suffered yellowish oily spots on the back of the leaves, which in turn developed into round hazel-to-brown lesions. The lesions on the front and back of the diseased section of the leaf were thrombocytic and crater-like. There were yellow-green halos in the surrounding area. Afterwards, the center of the lesion collapsed and became ulcer-shaped. Branch lesions showed no halo, but dark brown glaze. Lesions are similar to leaves. When the damage is severe, it causes fallen leaves, fruit drop and dead branches, and the whole plant and seedling tree die. The pathogens of pomelo canker are mainly lurking in the diseased tissues and overwintering. In the following year, the diseased parts of the pomelo shed pyogenic bacteria. They are transmitted through contact with wind and rain, insects, artificial instruments and foliage, and long-distance transmission is mainly based on seedlings, scions and fruit. The disease can occur from April to November. It is the most prosperous in mid-September. It is susceptible to the onset of summer shoots, followed by autumn shoots, early autumn shoots, late spring shoots, and spring shoots and winter shoots. High temperature and humidity will promote the outbreak of the disease. The most suitable temperature for the development of pathogens is 20-30°C. When the bacteria invade the new plant tissue, the water and humidity conditions are required. In general, the water film should be kept for more than 20 minutes. The bacteria mainly invade the wound, stomata and lenticels. Seedlings and young trees are more susceptible to the disease, and the older the age, the lighter the disease. Fresh shoots, young fruit with a diameter of less than 4.5 cm, and new shoots are generally no longer susceptible to disease. In the grapefruit plantation where the varieties are mixed, the shoots are inconsistent, the nitrogen fertilizer is excessive, or the management is extensive. The damage of leaf miners also contributed to the disease outbreak. 2. Control measures (1) Strictly implement the quarantine system. It is forbidden to transfer the grapefruit seedlings, rootstocks and scions out of the ward, and to prohibit the export of sick fruits. Once the diseased grapefruit, seedlings, scion or fruit are found, they are immediately destroyed. (2) Establish a disease-free nursery. The disease-free Shatian pomelo fine seed collection garden was selected to cultivate disease-free rootstocks and breed disease-free grapefruit seedlings. The introduction of disease-free grapefruit seedlings in the new planting grapefruit in Shatian is the most effective preventive measure. (3) New planted grapefruit garden focuses on prevention. Seedlings can be sterilized with 700-1000 mg/kg of agricultural streptomycin plus 1% alcohol for 15 minutes. If a disease-free zone is found for the first time in small quantities, it should be completely excavated and burned. Since then, it has been checked frequently. Once a sporadic disease strain is found, it should be immediately cleared and sprayed. (4) The arable land grapefruit should strengthen cultivation management. 1 Timely prevention and control of leafminers, swallowtail and other pests in each stage of pomelo shoots to reduce the wounds of branches and leaves to prevent the invasion of bacteria. 2 Do a good job of controlling shoots. The result tree is to wipe out the summer shoots thoroughly, and put the autumn shoots early. The diseased trees need to control the summer and autumn shoots, leaving more mature spring shoots. The application of potash fertilizer in the early stage of new shoots promotes shoots to be robust. 3 The diseased branches, diseased leaves and diseased fruits were cut off in time and burned in a concentrated manner. During the clearing of the garden in winter, fallen leaves, fallen fruits and dead branches were burned. Each cut off one diseased branch, that is, disinfect the branches with alcohol. 4 It is forbidden to enter the orchard when it is dry on rainy days or in the morning. (5) Chemical control. 77% can be used to kill 500 to 1000 times the liquid or 50% DT fungicide (cupric acid ferric copper) 500 times, 14% copper ammonia 250 times, 40% copper oxychloride 600 times, 12% Green milk copper 800 to 1000 times liquid, 1000 to 1500 mg/kg streptomycin for agriculture or 0.5% equivalent Bordeaux mixture. Matters needing attention: 1 cut off all the diseased branches, diseased leaves and fruit before spraying; 2 master the spraying period. Young trees should be sprayed for the first time at 3 to 5 centimeters after shoots at each shoot stage, sprayed every 5 to 7 days for the second time, and the leaves should be sprayed green for the third time. Mature trees were sprayed once at 10 days, 30 days and 60 days after flowering. The shoots were sprayed once a week for the leaf shoots in autumn and once in the green period. 3 Spray once after each pruning or after heavy winds and heavy rain.
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