Study On The Regularity Of Occurrence And Control Techniques Of Pear Scab On Baozhu Pear

With the fine quality and high yield, Baozhu pear is known as an excellent variety in Yunnan province. However, due to serious disease caused by pear scab (in past certain years the rates of infected leaves and fruits were up to 100% and more than 60% respectively), both the quality and yield of this variety of pear are not as excellent as they used to be. The negative influence of the scab on Baozhu pear is apparent.During investigating the occurring incidence of pear scab in Baozhu pear orchard, we analyzed the occurring pattern, and set up a linear model to demonstrate the relationship of different aerial moistures and the degree of occurring in field. Also a spatial distribution pattern of pear scab in Baozhu orchard was studied by using the means of three indices of aggregation(C, I.,k), Lloyd's mean crowding and index of patchiness, Iwao's patchiness and Tayor's law. And the model of sampling number was set up by Iwao's patchiness. Field trials of using fungicides were carried out as well to determine the effects of the fungicides used on pear scab and periods last for controlling pear scab on Baozhu pear cultivar. The following are the results of theses studies:1. The original occurring of pear scab took place in the. period of from middle of April to the early of May. Pear scab prevailed from July to September and ceased in October. There was no apparent difference of occurring on top, middle and lower layers of pear trees, so not as in all directions of pear trees.2. The occurring degree of pear scab was influenced by aerial moisture and rainfall. the linear model of different aerial moistures and the occurring degree in field was: y=0.3975x+68.146. The range of temperature was wide.3. In the mass, the spatial distribution of pear scab was well-proportioned distribution. The spatial distribution of pear scab was aggregated distribution in initial stages, and tends to well-proportioned distribution along with the ascent of density of pear scab.4. The model of sampling number was n=21.52/m-2.12. We can calculate the sampling number in different density.5. Field fungicide trials demonstrated that the control efficacies of 10% difenoconazole at 1: 3000 dilution, 40% flusilazole at 1:3000 dilution, and 50% kresoxim-methyl at 1: 4000 dilution were 87.52%, 83.16%, and 81.48% respectively. The control efficacies of 62.25% myclobutanil+80% mancozeb, 50%sulfur,and 50% carbendazim+sulfur were middle. The control efficacies of 10% polyoxinB and 50%iprodione were lower.6. The period of using fungicide was important for controlling pear scab, it is strongly recommanded in initial stage.