The objective of this study is trying to use the easily obtained biomaterials to prevent the occurrence of diseases in crops, especially strawberry, in Miaoli area, Taiwan. The best result of biomaterial applications will be recommended to the growers. Furthermore, to reduced the usage of chemicals in agriculture production and promote te development of non-synthetic resources. This year citrus extracts were used to prevent powdery mildew in strawberry. The results showed that citrus extracts could prevent the disease effectively. The extracts of Citrus aurantium L. cv. Hutou Gan dilutes 200 times have the best result, and could reduced powdery mildew infection rate from 97% to 9.5%.