Study On The Occurrence Regularity Of Apple Scab In Shaanxi And Hungicides Screening In Field

Apple scab, caused by Venturia inaequalis (Cooke) Wint., is one of the most serious diseases of apple in Shaanxi. Both leaves and fruits can be infected. Infected leaves may drop early and result in weakening trees with poor fruit production. Infected fruits are blemished and often severely deformed. This disease was listed as plant quarantine objective in Shaanxi in 1986. In recent years, apple scab has expanded to larger areas and severely threatening sustainable apple production in Shaanxi province. In order to persistently and effectively control apple scab, the characteristics of occurrence, damage, distribution and regularity of disease and its controlling fungicides screening were studied, and the main results obtained were as follows:1. Through investigating the occurrence and damage of apple scab in 33 counties in Shaanxi, the outbreak and distribution of this disease in main apple-growing areas of Shaanxi were fully understood. Results indicated that apple scab was very popular in most apple-growing areas in Shaanxi and the disease occurred in the north mouth of Qing-Lin Mountains and west of Wei-Bei plateau was much heavier than that in the west Guan-zhong plain and east Wei-Bei plateau, and it was found the disease least in east Guan-zhong plain. There was significant difference between the disease and cultivar. It was found that the disease on Fuji and Gala was heavier than that on Jonagold, Red Star and Qinguan.2. There was the symptom diversity of apple scab found in orchard investigation. Based on the response of apple tree and characters of pathogen, symptoms of apple scab were classified into six groups, including protuberant type, margin necrotic type, kraurotic type, chlorotic type, shuttle shape type and scab type. It showed that the symptom diversity of apple scab was close related to the pathogen infecting position of host, orchard ecological environment conditions and the resistance of apple cultivars.3. Apple scab in Xunyi county, Shaanxi province first appeared in second to third 10 days of May and there were two peaks of disease throughout apple growing seasons, one in the late June to early July and the other in second to third 10 days of September. The conditions of orchard ecological environment had great effect on disease occurrence and development, rainfall and temperature in particular.4. Based on results of fungicides applied to control apple scab in field trials, 10%difenoconazole WG, 43%tebuconazole WP, 40% Myclobutanil WP, 80%M-45 Mancozeband WP, 12.5%Diniconazole WP and 40% Flusilazole WP were found to have very good control efficiency to apple scab, among them, 10%difenoconazole WG was best.