STUDIES ON COMPATIBILITY OF PESTICIDE COMBINATIONS AGAINST MAJOR LEPIDOPTERAN PESTS AND SHEATH BLIGHT IN RICE”
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Date
2024-03-27
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Acharya N G Ranga Agricultural University
Abstract
The present study was carried out at Agriculture Research Station, Nellore
during late kharif, 2021 with an objective to determine the physical
compatibility, bioefficacy and phytotoxicity of the novel pesticides used against
major lepidopteran pests and sheath blight disease in rice.
Based on the physical compatibility of the pesticides viz.,
chlorantraniliprole, flubendiamide, cartap hydrochloride, azoxystrobin +
tebuconazole, azoxystrobin + difenconazole and their combinations they were
categorized into three classes viz., moderately acidic, neutral and slightly
alkaline. Cartap hydrochloride and its combination with fungicides resulted in
moderately acidic pH. Flubendiamide as a straight pesticide has slightly alkaline
pH and its combinations with fungicides resulted neutral pH. The rest of the
pesticides and combinations falls under the category of neutral pH along with
control (distilled water). All the treatments were found to be physically
compatible with no foaming, sedimentation and agglutination reactions.
Bioefficacy of the pesticides were determined by imposing the treatments
twice, one at 40 and other at 55 Days After Transplanting (DAT). Third spraying
at 70 DAT was not taken up as the pest status reached below Economic Threshold
Level (ETL). Per cent dead hearts and white ears were computed to study the
efficacy of pesticides against stem borer and per cent leaf damage against leaf
folder. To study the efficacy of combinations against sheath blight, Per cent
Disease Index (PDI) was calculated and then effect of these combinations on
natural enemies was recorded. Observations were recorded at one day before
spraying, 5 and 10 Days After Spraying (DAS). Chlorantraniliprole was found to
be equally effective against the stem borer followed by cartap hydrochloride,
flubendiamide and their combinations with fungicides. For leaf folder both
chlorantraniliprole and flubendiamide were found effective followed by cartap
hydrochloride and their combinations with fungicides. Sheath blight was not
prominent during the late kharif season at ARS, Nellore. So, artificial inoculation
xv
of the sheath blight (Rhizoctonia solani) was done. Pure culture of Rhizoctonia
solani was done on Potato Dextrose Agar and mass multiplication on the Typhal
grass bits.
The treatments azoxystrobin + difenconazole and its combination with
chlorantraniliprole were highly effective against sheath blight, followed by
azoxystrobin + tebuconazole. Rest of the combinations were on par in their
efficacy. These treatments have not shown negative impact on the survival of the
natural enemies and they found to have a striking increase rate of population
during first spray and second spray. Phytotoxicity experiment was conducted by
including double doses as treatments at 50 DAT, data was recorded at pre spray,
1, 3, 5, 7 and 10 DAS regarding the phytotoxicity symptoms like chlorosis,
yellowing, epinasty, hyponasty, leaf tip drying, leaf scorching and wilting.
Results concluded that no phytotoxicity symptoms were recorded.
Studies revealed that all the pesticides were physically compatible with
safe pH and bioefficacy of the pesticides holds good both as straight and
combination treatments. Thus, it is concluded that the efficacy of one pesticide is
not affected by the other pesticide. All these treatments were found safer to the
natural enemies and did not affect their survival. These pesticides don’t possess
any phytotoxic symptoms even applied at double doses.
Overall efficacy of the pesticide combinations is more which resulted in
higher yields in combination treatments compared to the straight treatments as it
controls both pests and diseases. Among the combinations, chlorantraniliprole
+ azoxystrobin + difenconazole resulted in 4992 Kg/ha, rest all other pesticide
combinations and straight insecticides resulted in equal bioefficacy with a yield
range of 3624 - 4408 Kg/ha. Lowest yield was recorded in untreated control
(2349 Kg/ha).