The rate of dissipation of pesticide varies with the nature of the pesticide, dosage, formulation and the application methods (Montemurro et al., 2002), crop variety (Fan et al., 2013; Wang et al., 2014), weather conditions (Garau et al., 2002) and frequency of pesticide applications. All the above factors influenced the residues of pesticide. Though, in the current study, the commercial formulation, dosage and application method was similar, the residue levels still varied in polyhouse and field conditions. This may be because, in polyhouse, the volatilization and wind drift losses of pesticides are much less in plant and soil. Since most of the pesticides are UV-degradable, in controlled condition there is likelihood that pesticides persist for a longer duration in absence of UV (IIHR, 2011) compared to open field conditions. Longer time for insecticide degradation on capsicum fruits in polyhouse condition compared to open field was also reported in other insecticides like, chlorantraniliprole, triazophos, spinosad, flubendamide, spiromesifen and thiamethaxam, chlorpyriphos, ethion, triazophos and profenophos (Kavitha et al., 2016). In a multi-location supervised field trials conducted on chillies (Pandher et al., 2012), the dissipation kinetics of deltamethrin 10 EC @ 17.5 and 35 g a.i./ha showed that the initial deposits of 0.21–0.49 mg/kg @ 17.5 g a.i./ha and 0.37–0.69 mg/kg @ 35 g a.i./ha reached BQL in 5 and 7 days. Similarly, residues of deltamethrin reached BQL of 0.01 mg/kg on the 7th day on tomato (Premchand et al., 1999) and 10 days on brinjal (Sen and Choudhary, 1999).
It was obvious that the initial deposits were directly proportional to the dose/ concentration of the sprayed chemical means the deposits of double the recommended dose was higher than that of the recommended dose. However, in the present study slight variation in initial deposits on capsicum fruits was recorded in polyhouse and open field. This might be due to the application method, and other abiotic factors. Dissipation studies of deltamethrin were also reported on tomato (Singh et al., 1989) and found initial residues of 0.07–0.09 mg/kg in single and 0.08–0.23 mg/kg in double the recommended dose. In cauliflower (Singh et al., 1990), maximum initial deposits recorded were 0.12 to 0.32 mg/kg, where as in cabbage (Singh et al., 1992) and brinjal (Das and Mukherjee, 2012) they recorded initial deposits of 0.08 to 0.30 mg/kg and 0.430 to 0.900 mg/kg, respectively.
The soil samples analysed at harvest of the capsicum fruits (40 days after 2nd spray) recorded no residues at both the growing conditions i.e., polyhouse and open field neither @ 150 ml (15 g a.i./ha) nor 300 ml (30 g a.i./ha) dose. This pesticide degradation in soil may depend on the organic matter content of the soil, soil pH or microbial fauna (Das and Mukherjee, 2012). Light is also a reason for pesticide degradation (photo-degradation), light also influences the soil characteristics (Gavrilescu, 2005). Studies also revealed that the higher moisture content of soil and soil microorganisms speed up the process of flubendamide degradation in soil (Das and Mukherjee, 2012; Katagi, 2004; Narenderan et al., 2020). In general, while applying the insecticides, insecticide release from the sprayer, drift of the chemical due to application procedures and wind was common, it may be the reason for insecticide to reach soil. Since, the capsicum vines are robustly grown and the foliage coverage was good, it is that likely higher absorption of insecticides on plant occurred surface than the accumulation in soil.