Abstract
Farmer's perceptions of pesticide usage in controlling yellow stem borer, Scirpophaga
incertulas (Walk.) in three rice growing districts, efficacy of some new generation
insecticides against the pest with compatibilities with natural enemies were carried out
during March 2013 to January 2016. A demographic survey showed that almost all the
farmers know the symptoms of stem borer and its control. Insecticide was found as a
common control practice where 19 brands were in use twice in a growing season with
recommended dose. Farmers are in the opinion that control of stem borer with
traditional insecticides is quite difficult. A few farmers followed IPM practices with a
little idea on the adverse effects of insecticides on natural enemies. Advices of pesticide
use are mainly from pesticide dealers or retailers and a very few farmers contact
government extension worker for this purpose. Three new insecticides namely
Chlorantraniliprole 0.4%G, Dinotefuran 20% SG and Methoxyfenozide 24% SC and two
commonly used insecticides such as Carbufuran 5G and Quinalphos 25 EC were tested
in the lab and field for their efficacy and compatibility with natural enemies. In lab test,
Chlorantraniliprole 0.4%G @ 27.88 mg/plant, Dinotefuran 20% SG @ 0.38 mg,
Methoxyfenozide 24% SC @ 1.0 µL, Carbufuran 5G @ 27.88 mg and Quinalphos 25 EC
@3.0 µL /hill gave above 80% mortality of YSB larvae. The field trial showed that
Chlorantraniliprole 0.4%G gave the maximum reduction of YSB infestation (dead heart
and white head) and maximum increase of yield over control followed by
Methoxyfenozide 24%SC, Dinotefuran 20%SG, Carbufuran 5G and Quinalphos 25EC.
In terms of comparative efficacy against target pest, different insecticides under
treatments showed ranking order as Chlorantraniliprole 0.4%G> Methoxyfenozid
24%SC> Dinotefuran 20%SG> Carbufuran 5G> Quinalphos 25EC. Application of
insecticides in different frequencies and times in the cropping season showed that all
the insecticides were found cost effective with twice spraying in the growing season at
the critical time of early vegetative stage and booting stage when 1-2 YSB moth and/1-2
egg mass found in the plot. Insecticides showed high persistence effect up to 5 days
after spraying (DAS) and then after certain time the reduction capabilities of infestation
exhausted. The new granular insecticide, Chlorantraniliprole 0.4%G was found the
most persistent than other new foliar spray insecticides. The selected doses of different
insecticides found effective against YSB caused the mortality of its two predators; lady
bird beetle and wolf spider as below 40% in the potted experiment and all the
insecticides reduced the individual number of predators viz., lady bird beetle, wolf
spider, carabid beetle, earwig, green mirid bug, damselfly and egg parasitoids viz.,
Trichogramma sp., Telenomus sp. and Tetrastichus sp. significantly over untreated control
plot. In all cases of field trial, Chlorantraniliprole 0.4%G was found least toxic and
Quinalphos 25EC was found high toxic on the natural enemies showing ranking order
as Chlorantraniliprole 0.4%G <Carbufuran5G <Dinotefuran 20%SG <Methoxyfenozide
24%SC <Quinalphos 25EC. On the basis of infestation reduced, grain yield increased,
long lasted persistence effect and least harmful effect on natural enemies;
Chlorantraniliprole 0.4%G proved the best of all the insecticides in YSB management
system although the study suggested minimizing its retail price for the enhancement of
cost effectiveness in the farmers' level among the different insecticides in the same line.