PhD

Studies on “Dissipation and risk assessment of select insecticides used for
pest management in cabbage and cauliflower” was conducted in College of
Agriculture, Vellayani, Cardamom Research Station, Pampadumpara and farmers
field at Kalliyoor during 2015-2018. The present research work was under taken
to study the dissipation of select insecticides viz., chlorantraniliprole 18.5 % SC,
flubendiamide 39.35 % SC, indoxacarb14.5 % SC, emamectin benzoate 5 % SG,
fipronil 5 % SC, quinalphos 25 % EC, cypermethrin 10% EC, acetamiprid 20%
SP, thiamethoxam 25 % WG and dimethoate 30 % EC in cabbage and
cauliflower, to assess their potential risks to human health, to determine their
effect on soil microbial activity, to estimate the residues in cooked samples and to
evaluate the efficacy of “Veggie Wash” to eliminate residues.
Survey conducted among 25 each of farmers cultivating cabbage and
cauliflower in plain (Thiruvananthapuram) and hill (Idukki) representing two agro
climatic conditions revealed that pest infestation was more in hills when
compared with plains. Accordingly, pesticide usage was higher in Idukki (84 %
each) than in Thiruvananthapuram district (12 and 8 %) in cabbage and
cauliflower respectively.
Dissipation studies of insecticides having label claim for cabbage and
cauliflower under CIB & RC in two agroclimatic regions of Kerala viz.,
Thiruvananthapuram and Idukki showed that the degradation of insecticides
varied with crop and chemistry of the insecticides. Insecticides persisted more in
cabbage under plain were flubendiamide (20 days) followed by acetamiprid and
quinalphos (10 days each), while in hills, higher persistence was observed in
flubendiamide, cypermethrin and quinalphos (10 days each). The lowest
persistence was observed in fipronil (3 days) in cabbage under plains and
acetamiprid (3 days) in hills. In cauliflower higher persistence was observed for
flubendiamide, chlorantraniliprole and dimethoate in plains and flubendiamide,
quinalphos (20 days each) and cypermethrin (15 days) treated plots in hills. The
lowest persistence was observed for emamectin benzoate (3 days) in cauliflower
under plains and hills.
Risk assessment study was carried out in cabbage and cauliflower using
selected insecticides under plains and hills by comparing the values of Theortical
Maximum Residue Concentration (TMRC) and Maximum Permissible Intake
(MPI). The result revealed that consumption of dimethoate and fipronil treated
cabbage and cauliflower were found to be risky to the end users. However, all
other insecticides are safe even on the same day of insecticide application.
Effect of insecticides on soil microbial activity was studied in cabbage and
cauliflower through the activity of urease, phosphatase and dehydrogenase
enzymes. Lower reduction in urease activity was observed in flubendiamide,
dimethoate and thiamethoxam treated plot and higher reduction was recorded in
fipronil and quinalphos treated plots over control both in cabbage and cauliflower.
However, lower reduction in phosphatase activity was recorded in flubendiamide,
thiamethoxam and cypermethrin and higher reduction was observed in indoxacarb
and fipronil treated plots over control. Lower reduction in dehydrogenase activity
was recorded in cypermethrin, acetamiprid and thiamethoxam treated plots and
higher reduction was recorded in indoxacarb and fipronil treated plots over contol
in both cabbage and cauliflower.
Study on extent of removal of insecticides through cooking from cabbage
and cauliflower was conducted with insecticides which had more persistence
revealed that 15 min cooking removed more residues and the highest removal was
observed for quinalphos (54.79 %) in cabbage under plains and cypermethrin
(66.47 %) in hills. However, in cauliflower the highest per cent removal was
observed for chlorantraniliprole (44.78) in plains and cypermethrin (52.32 %) in
hills. “Veggie wash” technology was evaluated in the cabbage and cauliflower
after application of insecticides at recommended doses revealed that dipping of
cabbage and cauliflower in one per cent “Veggie Wash” solution for 10 min.
followed by water wash removed 12-40 per cent of treated insecticides while
water wash alone removed 9 -35 per cent.
The present study revealed that the dissipation pattern of insecticides
varied with crop, agro climatic areas, and chemistry of the molecules. Risk
assessment study shown that insecticides viz., fipronil and dimethoate posed risk
on human health even at recommended dose. Studies on effect of insecticides on
soil enzyme revealed that except fipronil and indoxacarb, all other insecticides
under present study have less impact on soil enzymes. Decontamination studies
showed that cooking at 15 min. removed 50-60 per cent of insecticides and
“Veggie Wash” removed 12-40 per cent of treated insecticides. Present study
urged the need to evaluate the new insecticides carefully, by considering safety to
environment and human health. The risk assessment studies of all insecticides
should be done before going for field level recommendations.