How to prevent citrus, litchi, longan, ulcer disease?

How to prevent citrus, litchi, longan, ulcer disease?
Citrus ulcer disease symptoms: Leaves, yellow oil-like spots appear on the back of the leaves at the beginning, and gradually expand into nearly round shape later. The lesion penetrated the blade slightly on both sides, and the tissue was corked and rough. The central depression was cracked like a gray-brown crater. There are yellow halos around the lesion, with a diameter of 3- to 5-mm, and sometimes several lesions are linked together to form an irregularly shaped large lesion and the diseased leaves fall off earlier. Branches and lesions on branch shoots are similar to those on diseased leaves. They are nearly round, oval, or combined into irregular shapes, light yellow or yellow-brown, with prominent protrusions but no yellow halos around them. The lesions can reach deep into the phloem, and when the lesions surround the entire foliage, the shoots will die. The Fruit, lesions and leaves and shoots on the similar, the surface of corky protrusions and the central gap is more pronounced, when serious, causing fruit drop.
Ulcer disease is one of the most important diseases of fruit trees. It harms citrus, litchi, longan, and other fruit trees and poplars. The disease damages the leaves, shoots and fruits, often causing fallen leaves and dead branches, and even dead seedlings. The damage of orange fruit of mature horses caused serious fruit drop, light disease, and quality, resulting in economic losses. Citrus canker disease causes wounds from late March to November, especially high-temperature, rainy weather, and damage caused by pests such as leaf miners, which mainly damage new shoots and fruits.
The pathogen of ulcer disease is a kind of bacteria. The pathogen can survive in the host tissue for several months. The pathogenic bacteria latent in the diseased tissue overwinter. During the spring rains the following year, the bacteria spilled out of the disease and spread through wind, rain, insects, and foliage contact. Bacteria fall on young shoots, young leaves and young fruit, and are invaded by stomata, lenticels or wounds. In the case of high temperature and rainy conditions, the bacteria can be repeatedly infested and continue to expand. Tender shoots are 3–12 cm long, which is the period of invasive germs. Damage caused by leaf miners is an important way to infect the disease.
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. 100 times liquid or 1000-1500 mg/kg streptomycin or 0.5% equivalent Bordeaux mixture can be used. 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. Focus on grasping shoot stage and young fruit expansion period to protect young tissues and achieve control effects. (Author: Huai Bi)

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