MSc

ABSTRACT

The study entitled “Botanicals for the management of pests of brinjal, Solanum melongena L. was undertaken in the Department of Agricultural Entomology at College of Agriculture, Vellayani during the period 2018-2020 with an objective to manage the pests of brinjal using botanicals including formulation of cashew nut shell liquid (CNSL).

Laboratory evaluation of CNSL was done taking epilachna beetle (Henosepilachna vigintioctopunctata (F.)) and mealybugs as test insects of chewing and sucking type respectively. Cashew nut shell liquid (CNSL), a potential insecticide and a cheap by-product of cashew industry containing a mixture of phenolic compounds which was formulated into an emulsifiable concentrate formulation in Department of Agricultural Entomology, College of Agriculture, Vellayani was evaluated at different concentrations viz., CNSL @ 0.25, 0.5, 0.75, 1, 2, 3, 4 and 5 % against H. vigintioctopunctata and CNSL @ 0.05, 0.075, 0.1, 0.25, 0.75, 1 and 2 % against mealybugs. Emamectin benzoate 5 % SG @ 0.04 % and thiamethoxam 25 % WG @ 0.015 % served as the chemical check for epilachna beetle and mealybugs respectively.

Higher concentrations of CNSL (5 %, 4 %, 3 %, 2 % and 1 %) was found to be superior with mortality ranging from 53.33 to 80 per cent at 2 and 3 DAT when tested against H. vigintioctopunctata. At 5 and 7 DAT, 100 per cent mortality was recorded in chemical check, emamectin benzoate 5 % SG @ 0.04 % which was on par with CNSL 4 % and 5 %. CNSL 1 %, 2 % and 3 % also was on par, though inferior to the chemical check. CNSL at higher concentrations (1 - 5 %) produced high mortality ranging from 66.67 to 93.33 per cent of epilachna beetles under laboratory conditions.

Against mealybugs, at 2 and 3 DAT all the CNSL treatments were on par with each other with mortality percentage ranging from 0 to 26.67. At 5 and 7 DAT, CNSL treatments produced superior mortality over control. However, when tested against mealybugs, the chemical check thiamethoxam 25 % WG @ 0.015 % produced superior mortality at different intervals after treatments. At 7 DAT, higher concentrations of CNSL (1 % and 2 %) produced mortality comparable to chemical check.

Probit analysis was performed to find the dose mortality response. The LC50 and LC90 values of CNSL against H. vigintioctopunctata were 0.26 and 4.35 % respectively and that against mealybugs were 0.37 and 7.64 % respectively.

CNSL at different concentrations viz., 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2, 3, 4 and 5 % was applied on to brinjal plants and the phytotoxicity symptoms were scored as per CIB RC protocol where in no phytotoxicity was noticed at lower concentration ranging from 0.05 to 1 %. Slight (negligible) and moderate phytotoxicity were noticed in plants exposed to CNSL @ 2 and 3 % respectively. Plants treated with 5 % exhibited severe phytotoxic symptoms with severe necrosis and subsequent leaf fall.

Based on the results of laboratory and phytotoxicity evaluation, CNSL concentrations 0.25 % (LC50 value), 0.5 %, 1 % and 2 % were selected for further laboratory evaluation using H. vigintioctopunctata as test insect. Commonly used botanicals viz., neem oil 2 % and pongam oil 1 % and chemical emamectin benzoate 5 % SG @ 0.04 % were also tested. All the CNSL treatments except 0.25 % produced superior mortality over control at 2 DAT. At 3 DAT, CNSL 1 % and 2 % recorded significantly superior mortality than rest of the treatments and was on par with chemical check. At 5 and 7 DAT, all the CNSL treatments and neem oil 2 % produced mortality superior over control though inferior to chemical check. Pongam oil 1 % was found to be ineffective at all intervals.

A pot culture experiment was carried out in brinjal (Vellayani local) with effective CNSL concentrations selected based on the laboratory experiments. Combination treatment with neem oil (CNSL 0.25 % + neem oil 1 %, CNSL 0.5 % + neem oil 1 % and CNSL 1 % + neem oil 1 %) were also tested. Emamectin benzoate 5 % SG @ 0.04 % and thiamethoxam 25 % WG @ 0.015 % served as the chemical checks. Two rounds of application one each at vegetative and reproductive phase were administered.
In vegetative stage, there was no major pest incidence. In reproductive stage CNSL 1 % and chemical check emamectin benzoate 5 % SG @ 0.04 % found superior with lowest pest (H. vigintioctopunctata) population at 2 DAT. All other CNSL treatments and the combination treatments found superior over control though inferior to chemical check. At 3 and 5 DAT, CNSL alone (0.5 % and 1 %) was found to be superior and equally effective as that of chemical check. All combination treatments of CNSL with neem oil 1 % were also found to be effective. There was no significant difference between the treatments in managing mealybugs and the crop yield was also not significant among treatments. Phytotoxicity evaluation in pot culture studies had recorded no phytotoxicity. Analysis of biometric parameters (plant height, internode length, number of leaves and yield) did not exhibit any adverse effect on plant growth upon treatment with CNSL. CNSL treatments @ 1 % or below neither produced phytotoxic effect nor affected the growth characteristics of brinjal. Thus CNSL @ 1 %, can be used as a botanical pesticide against pests of brinjal.