Bioefficacy of natural products and biopesticides against Pieris brassicae L. infesting cauliflower
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Date
2020-10-17
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palampur
Abstract
The present investigations entitled “Bioefficacy of natural products and biopesticides against
Pieris brassicae L. infesting cauliflower” were undertaken during the year 2019-20 in Department
of Entomology, CSK Himachal Pradesh Krishi Vishvavidyalaya, Palampur. Intrinsic toxicity of
Agniastra and Brahmastra, azadirachtin, Bacillus thuringiensis, Beauveria bassiana,
diafenthiuron and spinosad was worked out against neonate larvae of P. brassicae by leaf dip
method of bioassay. Based upon LC50 values, the LC50 values of spinosad was found to be
minimum (0.034 ppm), followed by diafenthiuron (0.059 ppm), azadirachtin (1.031 ppm), Bt
(5.214 ppm), B. bassiana (1.723 x 108
cfu g/lit.), Agniastra (3508.232 ppm) and Brahmastra
(3720.866 ppm). Evaluation of natural products, biopesticides and insecticides against P.
brassicae on cauliflower (var. Maharani F1 Hybrid) was carried out under field conditions.
Prophylactic sprays of natural products and azadirachtin were started 30 days after transplanting
whereas application of Bt, B. bassiana, diafenthiuron and spinosad was started with the
appearance of pest and repeated at an interval of 10 days. On the basis of 4 sprays, minimum
larval population per plant was observed in diafenthiuron (3.19), followed by spinosad (3.30),
azadirachtin (7.20), Bt (7.60), Agniastra (10.61), B. bassiana (11.16) and Brahmastra (11.39). The
highest per cent reduction in larval population over untreated check was observed in spinosad
(69.16%), followed by diafenthiuron (68.31%), azadirachtin (49.83%), Bt (47.81%), Agniastra
(37.19%), Brahmastra (35.95%) and B. bassiana (35.48%). Cauliflower curd samples were
collected from diafenthiuron (0.05%) and spinosad (0.015%) treated plots at 0 (2 hrs), 1, 3, 5 and
7 days after 3rd spray. The residues were determined by HPLC. The average recovery of
diafenthiuron was 84.61 per cent and it was 84.56 per cent for spinosad from fortified samples of
cauliflower curds. Limits of quantification (LOQ) for diafenthiuron and spinosad were worked out
to be 0.033 and 0.011 mg/kg, respectively. Initial residues of diafenthiuron were 0.5144 mg/kg
which dissipated to 0.3418, 0.2331 and 0.0339 mg/kg after 1, 3, and 5 days of application,
respectively. Initial residues of spinosad were 0.4669 mg/kg which reduced to 0.2504, 0.1207 and
0.0603 mg/kg after 1, 3, and 5 days of application, respectively. Half-life values of diafenthiuron
and spinosad were calculated to be 1.94 and 2.23 days, respectively. Safety intervals of 2 days for
diafenthiuron and 10 days for spinosad are suggested for safe consumption of cauliflower