Exploring novel pesticide mixtures to combat emerging pest complex in Rice (Oryza sativa L.)
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Date
2022-03-07
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Department of Entomology, OUAT, Bhubaneswar
Abstract
Two major pests, brown planthopper (BPH) and yellow stem borer (YSB) coexist in the late tillering stage of rice. Insecticide combinations are the most effective way to manage pest complex having different feeding behavior. This study investigated the compatibility of insecticide (chlorantraniliprole, triflumezopyrim, flonicamid and pymetrozine) formulations in mixtures. The insecticide mixtures were physically and chemically compatible and did not produce phytotoxic effects on rice plant. The experiment was conducted in laboratory and field of ICAR-National Rice Research Institute, Cuttack in two seasons of kharif 2019 and 2020. The toxicity of the insecticides in combination and alone against BPH and YSB was studied. The lethal doses (LD50) were 17.215, 0.059, 0.180 and 0.036 ng per insect for Chlorantraniliprole, Flonicamid, Pymetrozine and Triflumezopyrim against BPH, respectively. Similarly, LD50 were 2.737, 0.073, 0.313 and 0.061 ng per larva against YSB, respectively. The mixture of 17.215 ng Chlorantraniliprole + 0.059 ng Flonicamid per insect resulted in maximum mortality of BPH (86 %). The highest mortality of YSB was recorded in the treatment of 2.737 ng Chlorantraniliprole + 0.061 ng Triflumezopyrim per larva (86.67%). Two mixtures of Chlorantraniliprole + Triflumezopyrim (15 + 18.75 g a.i ha-1 and 22.5 g + 12.5 g a.i ha-1) were the most effective in managing BPH and YSB, respectively in field conditions. The residues of the insecticide mixtures in rice plant, soil, water, straw and grains were estimated using QuEChERs method in liquid chromatography-triple quadrupole tandem mass spectrometry. The dissipation pattern of all the mixtures (chlorantraniliprole + triflumezopyrim, chlorantraniliprole + flonicamid and chlorantraniliprole + pymetrozine) followed first order kinetics. Overall, the half-lives of chlorantraniliprole, triflumezopyrim, flonicamid and pymetrozine (both in single application and mixtures) ranged from 8.85-12.67 days in plant, 14.29-27.94 days in soil, 10.31-17.76 days in water. The residues of the mixtures in rice straw were below the detectable limit and in rice grains was below the Maximum Residue Limit (MRL). The insecticide mixtures at reduced doses were safe to the environment and the grains were safe for human consumption. Mixtures were safe to natural enemies (mirid bugs and spiders) in rice ecosystem. Pesticide combinations had increased toxicity and could reduce the quantities of individual pesticides and thereby, lowering the crop production costs. Pesticide mixtures could also be considered safe to the environment.