Pear ring rot is a serious disease in pear producing areas in China, especially in high temperature, high humidity and coastal fruit producing areas. The incidence of diseased plants in individual orchards is as high as 80%, and the fruits stored after harvest continue to get sick. It can also harm apple, hawthorn, peach, plum, apricot, chestnut, jujube, begonia and other fruit trees. Injury symptom: 1, injury site: mainly damage branches and fruits, leaves are rare. 2. Branch damage: Brown bumps are generated around the lenticels at the initial stage, which gradually expand to form lesions with a diameter of 0.5 ~ 3 cm (mostly 1 cm), which are nearly round or irregular, reddish brown to dark brown. The center of the lesion is tumor-like, hard in texture, and most of the edges are divided into annular grooves. The following year, the area around the lesion swelled, the crack of the lesion deepened, the lesion tissue tilted like a "saddle", and many small black spots (conidia and ascomycetes) were produced on the surface of the lesion. Sick tissue can usually be peeled off. When the branches are seriously damaged, the skin lesions are often contiguous and the epidermis is very rough. 3. Fruit disease: the fruit is damaged, and the symptoms mainly appear near maturity or storage period. At the initial stage, water-stained brown spots are formed, which are nearly round. The diseased spots spread rapidly, gradually becoming light brown to reddish brown, with obvious concentric wheel lines, and soon the whole fruit rotted. The lesion is not sunken, the diseased tissue is soft and rotten, and it often emits sour smell and brown juice flows out. On the surface of the affected area, there are scattered small black spots arranged in a wheel shape. Chinese alias: ring rot, pellagra, ring brown rot and verrucous pellagra harm crops: pear, peach, plum, apricot, chestnut, jujube, begonia and other fruit trees. Harmful symptoms: ring rot mainly harms branches and fruits, with relatively few leaves. Branches (trunk, main branch, lateral branch and twig) are diseased, and the lesions are centered on lenticels, forming oblate or oval reddish-brown lesions with a diameter of 3 ~ 30 mm The lesions are hard in texture, prominent in the center, such as warts, with cracks at the edges, and often form annular grooves with healthy tissues. In the second year, many small black spots (conidia) were produced in the center of the lesion. The crack between the lesion and the healthy part gradually deepened, and the diseased tissue tilted like a saddle. Many lesions are often linked together, making the epidermis look rough, so it is called pachydermia. Lesions generally only invade the surface layer of bark, and even invade the cortex in severe cases. After the disease occurred, the tree vigor was seriously weakened, and even the branches gradually died. Fruits are more likely to get sick than those that are close to maturity and storage. When the fruit is damaged, it also takes the lenticels as the center, producing waterlogged brown spots, which quickly expand into concentric wheel-shaped disease spots with light brown or brown alternation, and brown mucus overflows. When the conditions are right, the whole fruit can rot in a few days, often emitting a sour smell. Under the central epidermis of the affected area, black particles (conidia) are gradually scattered. The diseased fruit is rotten and juicy, and turns black and hard after losing water. Leaf diseases produce nearly round brown spots with concentric wheel lines or irregular brown spots with a size of 0.5 ~ 1.5 cm. The lesion gradually turned gray and grew small black spots. When there are many diseased spots on the leaves, it often causes dryness and early autumn. Classification attribute: The solid shell of pear belongs to Ascomycetes subfamily, and the asexual stage belongs to Hemiptera Macropora. Distribution: It occurs in Zhejiang, Jiangsu, Shanghai, Jiangxi, Anhui, Sichuan, Yunnan, Shandong, Shanxi, Beijing, Tianjin, Hebei, Henan, Liaoning, Jilin and other provinces and municipalities directly under the Central Government, especially in North China, Northeast China and East China. Pathogenic characteristics: pathogenic bacteria overwinter on the damaged branches with hyphae, conidia and ascomycetes. In spring, germs first infect branches and then fruits. Most fruits infected by pathogenic bacteria are concentrated in June-July. If the young fruit period coincides with frequent rainfall, there will be more spores and more infections. Young fruits do not get sick immediately after being infected, but are in a latent state after being invaded by germs. When the fruit is close to maturity, after physiological and biochemical changes occur inside it, the latent hyphae spread rapidly and the fruit becomes ill. The harvest period of fruit is the peak period of field diseases, and the storage period of fruit is also the main occurrence period of diseases. The incubation period of early bacterial infection is as long as 80 ~ 150 days; The incubation period of late infection is only about 18 days. The reason why the pathogen does not spread in young fruits is related to the phenol content and sugar content in fruits. When the content of phenol in fruit is above 0.04% and the content of sugar is below 6%, the pathogen is inhibited. Instead, it is conducive to the spread of latent bacteria. The peak of the disease appeared after the content of phenols dropped to the lowest and the content of saccharides rose to the highest. Epidemic dynamics: The occurrence and prevalence of ring rot are closely related to climate, tree potential and varieties. (1) In the early stage of fruit growth, there are many times of precipitation, early onset peak, more spores and more infections. If the mature period encounters high temperature and drought, ring rot will occur seriously. On the contrary, bacterial infection is less and the incidence is lighter. In Hebei Province, the annual incidence of rainy days from May to July is relatively high. On the contrary, the incidence rate is low in dry years. (2) Rhizoctonia solani is a weakly parasitic pathogen, and the weak plants, old diseased branches and young trees replanted in old diseased orchards are susceptible to diseases. Orchard management is extensive, there are too many fruits, improper fertilization, especially partial application of nitrogen fertilizer, and there are many diseases. Young trees and strong branches seldom get sick. (3) There are differences in disease resistance among apple varieties. Red star, marshal, golden crown, green banana, India and other varieties are more susceptible to disease; Guoguang, Zhuguang and other varieties have mild diseases. Prevention and control methods: apple ring rot infects both branches and fruits, and the focus of its loss is fruit damage, but the disease of branches is closely related to the disease of fruits, so the prevention and control of apple ring rot should take into account. (1) The initial infection of Rhizoctonia comes from diseased branches. Clearing the diseased tumor is an important preventive measure. Fruit trees should be sprayed with fungicides during dormancy, such as Olek-Guo Liangan of Aofeng Company, and the stock solution can be smeared. (2) Strengthen cultivation management, improve the disease resistance of trees, and pay attention to the selection of disease-free seedlings in new orchards. If a diseased plant is found, it should be eradicated in time to prevent further spread. Nursery should be located far away from the disease area to cultivate healthy seedlings without diseases. When pruning young trees, it is forbidden to use diseased branches as pillars, and it is not appropriate to pile the pruned diseased branches near the new fruit area. (3) Spray protection: Generally, spray the medicine for the first time from the end of May, and then spray it for 3 ~ 5 times in combination with the prevention and treatment of other diseases. The best medicine to protect fruits is Bordeaux mixture (1: 2: 240). In addition, 250 times diluted solution of 25% bactericidal Dan wettable powder, 800 times diluted solution of 50% carbendazim wettable powder, 50% carbendazim wettable powder 1 0,000 times diluted solution, 800 times diluted solution of 50% thiophanate-methyl wettable powder, 800-/kloc-0,000 times diluted solution of M-45 wettable powder, and 35% diluted solution. Other fungicides can be used at this time. In actual control, it is best to use more than two kinds of chemicals alternately to improve the efficacy. (5) After preventing the fruits in the field from getting sick during storage, pay attention to removing the diseased fruits and burying them deeply. When preparing fruits for storage and transportation, diseased fruits and other damaged fruits must be strictly removed. Then stored at low temperature, and stored at 0-2℃ can completely control the disease. With the help of microscope, it can be identified in the field according to its special habits, damage and morphological characteristics of female adult mites.