G. M. Das

Bio: G. M. Das is an academic researcher. The author has contributed to research in topics: Population. The author has an hindex of 1, co-authored 1 publications receiving 26 citations.

Occurrence of the red spider, Oligonychus coffeae (Nietner), on tea in north-east India in relation to pruning and defoliation.

Abstract: The red spider, Oligonychus coffeae (Niet.), persists in all stages of its development on a few old leaves and ‘ janams ’ (small leaves at the base of the shoot) of tea bushes during the cold weather, and this persisting population is primarily responsible for the attack in the spring.In pruning, a great many of the old leaves (including janams) are removed from bushes, and, concomitantly, the red spider. Pruned tea is, therefore, less attacked than unpruned tea or ‘ skiffed ’ tea (where just a little is cut off the tops of the shoots) in which comparatively more leaves are left on bushes.

Ecology of tetranychid mites and their natural enemies: a review iii. biology, ecology and pest status, and host plant relations of tetranychids

Abstract: The literature pertaining to the bionomics of some of the most important tetranychids is reviewed. Considerable attention is paid to the possibilities of spider mites reaching pest levels as a result of environmental factors. It is concluded that more information is needed on economic injury levels of various species on different crops and under various climatic conditions. The influences of cultural practices and their interactions as related to population development of tetranychids also need more study. Furthermore, work is needed on the influence of climatic conditions on development of tetranychid mite populations together with possible predictability of outbreak situations. Finally, we need to know more about the fundamental relations between the host-plant quality and spider mite development, and the impact of spider mites on the development of their host plants.

Insect pests of tea and their management.

Abstract: Globally, 1031 species of arthropods are associated with the intensively managed tea Camellia sinensis (L.) O. Kuntze monoculture. All parts of the plant, leaf, stem, root, flower, and seed, are fed upon by at least one pest species, resulting in an 11%-55% loss in yield if left unchecked. There has been heavy use of organosynthetic pesticides since the 1950s to defend the plant against these pests, leading to rapid conversion of innocuous species into pests, development of resistance, and undesirable pesticide residues in made tea. As a result of importer and consumer concerns, pesticide residues have become a major problem for the tea industry. Integrated pest management (IPM) may help to overcome the overuse of pesticides and subsequent residues. We review the advances made in our understanding of the biology and ecology of major insect and mite pests of tea, host plant resistance, cultural practices, biocontrol measures, and need-based application of botanicals and safer pesticides to understand the present status of IPM and to identify future challenges to improvement.

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

Abstract: 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.

The red spider mite, Oligonychus coffeae (Acari: Tetranychidae): its status, biology, ecology and management in tea plantations

Abstract: Oligonychus coffeae Nietner (Acari: Tetranychidae), the red spider mite (RSM), is a major pest of tea (Camellia sinensis) in most tea-producing countries. Nymphs and adults of RSM lacerate cells, producing minute characteristic reddish brown marks on the upper surface of mature leaves, which turn red in severe cases of infestation, resulting in crop loss. The pest is present on tea all the year round, although numbers vary depending on season. Their number increases as the weather warms up and decreases markedly once rains set in. Under optimal conditions there may be 22 overlapping generations in a year. Parthenogenesis is known to occur; consequently, all mite stages can be found at a given time. Their infestation is mainly confined to the upper surface of the mature leaves and could readily be identified by the bronzing of the leaf. There are several naturally occurring insect predators, such as coccinellid and staphylinid larvae, lacewing larvae, and mite predators, most importantly species of the families Phytoseiidae and Stigmaeidae. Integrated management has been adopted to control this mite pest, involving cultural, mechanical, physical, biological and chemical methods. This review collates the most important works carried out on biology, ecology and management of O. coffeae. Also the scope of future studies for better management of this regular mite pest of tea is discussed.

Field efficacy of a biopesticide prepared from Clerodendrum viscosum Vent. (Verbenaceae) against two major tea pests in the sub Himalayan tea plantation of North Bengal, India

Abstract: The toxicity of four concentrations (1, 5, 10 and 20% w/v) of an aqueous extract from the weed, Clerodendrum viscosum Ventenat (Verbenaceae) was investigated under field conditions of the North Bengal University, Darjeeling, West Bengal, India for managing two major pests of tea, Camellia sinensis (L), namely the tea mosquito bug, Helopeltis theivora Waterhouse, (Heteroptera: Miridae) and the tea red spider mite, Oligonychus coffeae Nietner, (Acarina: Tetranychidae). Four field trials, two for red spider mite and two for tea mosquito bug, were conducted during April–May 2008 and October–November 2009 following a Randomized Block design. The aqueous extract of C. viscosum effectively and significantly reduced the mite population as well as infestation of tea mosquito bug by 68–95% and 73–86%, respectively, and their bioefficacy is comparable to synthetic and neem pesticides. No phytotoxic effect (score 0–5% and grade 1) was observed in the tea bushes sprayed with different doses of aqueous extract of C. viscosum in the field. Made tea samples were taint free. Organoleptic test revealed leaf-infusions and liquor strength as good, scoring 6.5–7.0 on a 10 point scale. Availability and distribution of this weed (C. viscosum) in and around tea-growing areas of sub Himalayan region, along with its processing for the feasibility of including C. visosum extracts in the current IPM programme is discussed.