Effects of some insecticides and the application methods on the control of rice leaffolder,Cnaphalocrocis medinalis.

The objective of this study is to compare the effects of 31% fipronil triazophos on the control of rice leaffolder Cnaphalocrocis medinalis Guene with some common insecticides,and to compare the effectiveness of different application methods.The experimental results demonstrated that:(1) 48% chlorpyrifos EC possessed the quicker knockdown effect on C.medinalis than other insecticides tested.The optimal controlling effect(OCE) was observed at one day after treatment with chlorpyrifos and at 3 days after treatment with the mixture insecticides of triazophos,fipronil and hexaflumuron(31% triazophos,fipronil ME,21% triazophos and fipronil EC,15% hexaflumuron and triazpphos EC).(2) All treatments provided the OCE at 3 days after application with the following effectiveness order: 31% triazophos and Fipronil ME at 1.5 L/hm2 31% triazophos and fipronil ME at 1.05 L/hm2 21% triazophos and fipronil EC at 1.5 L/hm2 48% Chlorpyrifos EC at 1.5 L/hm2 15% hexaflumuron and triazophos EC at 1.5 L/hm2 15% chlorpyrifos and abamectin EC at 1.5 L/hm2.(3) All the insecticides tested provided over 91% of control to the larvae under the 1st instar(at the time of insecticide treatment).When applying to the 2nd-3rd instar larvae,31% Triazophos and Fipronil ME provided the controlling effectiveness of 90%;the effectiveness for the rest of the treatments declined remarkably.When sprayed in fine mist,31% triazophos and fipronil ME(1.5 L/hm2) still could maintain its effectiveness of 95.6% against the 4th instar larvae.In comparison,all the other treatments had lower controlling effects.(4) The application method of fine mist spray could enhance the controlling effect of 31% triazophos and fipronil ME to C.medinalis,especially for older larvae.Compared with the conventional sprayer'Gongnong 16' at 1.8 mm of nozzle diameter,the fine mist sprayer(nozzle diameter = 1.2 mm) and'Dongfanghong 18' fine mist sprayer increased by 5.5% and 7.8% of the controlling effect at 3 days after treatment,respectively.The fine mist spray with Dongfanghong 18 increased by 4.7% and 20.8% of the controlling effect to the 1st-2nd instar larvae and the 4th～5th instar larvae,respectively.