What disease is the blackening of snow pear leaves and how to prevent it?

It may be pear black spot disease. Pear black spot disease is a common disease of Japanese and Korean pears and snow pears, belonging to the genus Alternaria. Harmful to leaves and fruits. The disease begins in mid to late May in the northern fruit area, and the peak period of the disease is from July to August. Generally, the disease is more severe in autumn, and it occurs earlier and more severe in years with high temperature, high humidity, and early rainfall. Prevention and control measures: prioritize the prevention and control of spring shoot leaf diseases.1. Agricultural prevention and control: timely plowing and weeding, removing dense branches, and improving ventilation and transparency. Clean the orchard after falling leaves and sweep away the fallen leaves.2. Chemical control: Focus on protecting spring shoots and leaves, while autumn shoots and leaves only need to be controlled in the early stages of growth. Excessive use of drugs is not advisable. The available pesticides include: 1.5% polyoxytocin 300-500 fold solution, 10% polyoxytocin 1000 polyoxytocin 1500 fold solution, 4% agricultural antibiotic 120 fruit tree specific 600-800 fold solution, and 5% chlorhexidine wettable powder 1000 fold solution. The above drugs can all be added 3000 times with organic silicon penetrating agents, increasing the efficacy.3. Spraying period: These pesticides should be mainly composed of antibiotics, and other drugs should be used alternately. Spray immediately after the first drop of flowers, the second in mid May, and the third in late June or early July during the early growth of autumn shoots.4. Spray protective agent: Spray twice with 1:3:240 Bordeaux liquid on sunny days in June, with an interval of 15-20 days. Continue spraying protective agent 1:3:240 Bordeaux solution 1-2 times on sunny days in July, with an interval of 15-20 days. During the rainy season, fungicides can be sprayed on trees 1-2 times, mainly with a solution of 1.5% polymycin 300-500 times and organic silicon 3000 times, and other fungicides can be used alternately.