Study on Optimum Sprayed Period of Pesticide against Laodelphax striatellus in Rice Panicle Stage

To identify the proper time of protecting rice from Laodelphax striatellus in panicle stage,using rice variety Yongyou No.12 as the test material,1 125 mL/hm2 of 25% pymetrozine wettable powder and 225 g/hm2 of 40% chlorpyrifos EC were sprayed in 5 different periods of rice including 5 days before break(August 26),break stage(August 31),full heading stage(September 7),5 days after heading(September 12) and 10 days after heading(September 17).The field efficacy of different spraying stages to control Laodelphax striatellus in rice panicle stage was studied.The results indicated that there was no significant effects on reducing the insect density applied pesticides in 5 days before break and break stage,and the Laodelphax striatellus was effectively controlled applied from full heading stage to 5 days after heading.Therefore,the optimum sprayed period of pesticide against Laodelphax striatellus in rice panicle stage was within 10 days after heading when using the pesticides of 25% pymetrozine wettable powder 225 g/hm2 and 40% chlorpyrifos EC.