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Acharya N G Ranga Agricultural University
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).