Pesticide usage pattern in tea ecosystem, their retrospects and alternative measures.

Tea is a perennial plantation crop grown under monoculture providing favorable conditions for a variety of pests. The concept of pest control has undergone a considerable change over the past few decades. In recent years there has been a greater dependence on the use of pesticides (7.35-16.75 kgha(-1)) with little importance laid on other safe control methods for the management of tea pests. Due to this practice, the tea pests showed a higher tolerance/ resistance status due to formation of greater amount of esterases, glutathione S-transferase and acetylcholinesterase. Thus, over reliance on pesticides end up with pesticide residue in made tea (DDT - 10.4-47.1%; endosulfan - 41.1-98.0%; dicofol- 0.0-82.4%; ethion - 0.0-36.2%; cypermethrin - 6.0- 45.1%). The growing concern about the pesticide residue in made tea, its toxicity hazards to consumers, the spiraling cost of pesticides and their application have necessitated a suitable planning which will ensure a safe, economic as well as effective pest management in tea. At present it is a global concern to minimize chemical residue in tea and European union and German law imposed stringent measures for the application of chemicals in tea and fixed MRL values at < or = 0. 1 mgkg(-1) for the most commonly used pesticides which will not be met out in the real practice and has been a major constraint to tea exporting countries like India. In order to regulate the situation of the Indian market at global level, central insecticide board and prevention of food adulteration regulation committee have reviewed the MRL position for tea and has recommended 10 insecticides, 5 acaricides, 9 herbicides and 5 fungicides for use in tea and issued the tea distribution and export control order 2005 which will help the country to limit the presence of undesirable substances in tea. This review attempts to provide the readers with a comprehensive account of pesticide use in North East in tea, surveillance report of the European community regarding the residue level in Assam and Darjeeling tea, recent amendments by international and national regulatory bodies, revised MRL values of pesticides in tea, an update about the current strategies for the management of tea pests with more focus on the use of biological control agents and a possible beneficial role or judicious use of chemical pesticides in complement with other alternative measures to achieve optimum effects in terms of limiting agricultural input, lowering production costs, reducing environmental contamination and the effect on non-target organisms, delaying the development of resistant pest biotypes and above all minimizing the pesticide residues in tea to increase the exports.

Influence of chemical profiles of host plants on the infestation diversity of Retithrips syriacus.

The onset of biotic stress in the host plants as a result of increased insect population size leads to enhanced levels of secondary metabolites and associated phenolic enzyme activity· Of the three host plants examined, viz. Ricinus communis (castor), Eucalyptus globulus (eucalyptus) and Manihot utilissima (tapioca), castor was the host most preferred by Retithrips syriacus· Despite the fact that tapioca had the highest levels of secondary compounds, thrips infestation persisted· However, fecundity and growth were reduced because of the relatively high levels of primary metabolites. Gallic acid was found to be the most toxic of the phenolic acids, followed by pyrogallol, resorcinol, phloroglucinol and vanillic acid· The less toxic phenolic acids and flavanoids were detected in leaves that harboured thrips, while the preponderance of gallic acid was found in uninfested hosts. Thus the interaction of Retithrips syriacus with the hosts is governed essentially by the biochemical profiles of its hosts, which tend to be altered subsequent to infestation, thus manifesting induced resistance through enhanced production of phenolics.