Determination of the Economic threshold of the rice stem borer (chilo suppressalis) in early and late maturing using biological and chemical control methods.

Due to the importance of rice in the economical, political and food security situations in country especially Northern provinces which have agriculture as its main economical base, paying attention to reduce pests damages especially rice stem borer as the main pest of rice is very important. Though there is enough information on the pest biology, physiology, ecology and natural enemies ,there has not been enough work done on integrated pest management (IPM). IPM is a system in which all the possible suitable techniques and methods are being used to decline the pest population below the economic injury level. Therefore, threshold and economic injury level is considered as the base for decision making in IPM. To establish the best control method in two provinces of Gilan and Mazandaran two varieties of rice were chosen: biological and chemical control methods. The research included two treatments, one under the cage and the otherone outside the cage (without any control measures) by factorial statistical methods using completely randomized block designs. Under the cage pest population and number of generations in each treatment and region was considered. Treatments included one cluster to five clusters of pest eggs per square meter and a control with four replications for determination of the relation between the pest population and yield reduction on the basis of regression and threshold of profitability using Pedi go and Stone equation. To make the Economic threshold of various varieties applicable national parasitism coefficient was considered and showed in the final table. Economic injury level was determined by using two methods: observed prices and predicted prices using econometric method. There was not significant difference observed between them. Economic injury threshold level calculated in the biological and chemical methods showed that biological control method stays at a lower level.control criteria calculated in Gilan province for first and second generation of pest on Hasani variety in chemical control method was 2.01 and 1.73 larva in square meter respectively and in biological control method was 1.65 and 1.21 . For Sepidrod variety in first and second generations of pest was 2.28 and 2 in chemical control method and 2.20 and 1.92 in biological control method. for Mazandaran province in Taroom variety was 2.09 and 1.62 in chemical control method and 1.96 and 1.42 in biological control method and finally in Nemat variety for first,second and third generations was 1.99, 1.2 and 1.97 for chemical control method and 1.82,1.1 and 1.83 for biological control method respectively . Keywords:Threshold,Economic injury,Rice,control management,Pest,Gilan province,Mazandaran province,Chemical control,Biological control ,stem borer : Abstract