The effectiveness of Trichoderma atroviride, T. asperellum, T. harzianum, against targeted tea disease causing pathogen, Fusarium solani (dieback), Beauveria bassiana against tea mosquito (Helopeltis theivora), and Metarhizium anisopliae against the red spider mite, Oligonychus coffeae Nietner, and the live wood eating termite (Microcerotermes beesoni Snyder), respectively were evaluated under laboratory and field conditions. The Trichoderma isolates showed effective control of F. solani (64.6 to 71.7%) under laboratory conditions, while the wettable powder (WP) formulation could reduce dieback disease incidence (57.1 to 77.7%) over control, under field conditions. The post prune application of Trichoderma asperellum on light pruned (LP) and application of T. asperellum as well as T. harzianum on deep skiffed (DS) tea fields showed a significant growth promotional response. The treated bushes could produce an average number of 421.2 and 398.4 shoots when it was applied 7.5 and 5.0% (w/v), respectively, which was higher than the number of shoots recorded in the control plots (259.4). The antagonist also induced comparatively higher shoot length (6.85-7.99 cm) than the untreated control plots (5.13-6.38 cm). The B. bassiana isolates (2 × 10 9 conidia/ml) exhibited 71.5 to 93.0% control of 2nd instar nymphs of H. theivora under in vitro conditions. However, addition of different adjuvants resulted in enhanced mortality. Under field conditions, the highest reduction of tea mosquito population of 52.3% was noted when B. bassiana (1 × 10 9 cfu/ml) was sprayed along with Tween 20 plus and crude sugar. However, the wettable powder formulation of this EPF along with jaggery reduced the insect incidence. The M. anisopliae effectively controlled the red spider mite to the tune of 46.3 to 63.8% under laboratory conditions, while the wettable powder formulation of this isolate was more effective against the termite, resulting in the reduction of infestation to the tune of 84.2% under field conditions.

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A b s t r a c t A r t i c l e I n f oThe grey blight, caused by Pestalotiopsis theae is a serious problem in almost all tea growing regions of India. A large number of tea cultivars were found to be susceptible to this disease. Evaluation of four selected fungicides (carbendazim 12% a.i + mancozeb 63% a.i., hexaconazole 5 EC, copper oxychloride 50 WP and copper hydroxide 77 WP) have been found effective in suppressing the pathogen to the considerable degree under in vitro conditions. Results indicated that, maximum control (70.8%) was achieved in the case of combi fungicidal formulation (carbendazim 12% a. i. + mancozeb 63% a. i.) followed by hexaconazole 5 EC and copper hydroxide 77 WP and copper oxychloride 50 WP, respectively. Effort has been made to evaluate the effectiveness of the indigenous Trichoderma viride (KBN-24) and T. asperellum (KBN-29) in inhibiting the mycelial growth of P. theae in dual culture method and the results indicated significant inhibition of the pathogen. Results on the compatibility study indicated that the tested fungicides adversely affected the growth of T. viride to varying degree. The maximum inhibition (79.0%) was noted in case of combi fungicide formulation followed by copper oxychloride (75.8%) and hexaconazole (70.4%). Thus the results of this current investigation highlighted the fact that the local Trichoderma isolates were found effective in controlling the targeted phytopathogen. However, use of such fungicides soon after the application of Trichoderma formulation, should be discouraged to have a better control of the disease.

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Background: The dieback disease of tea caused by Fusarium solani is one of the major constraints in determining its production and quality. Genus Trichoderma is a promising biocontrol agent to control the dieback without any residual effect and is the most suitable option for integrated disease management approach. A few local Trichoderma spp were isolated from tea rhizosphere of the Dooars zone and preliminary identified. Based on dual culture bioassay, the most efficient isolate got re-identified from well reputed national institutes and its liquid formulation (2% Aqueous Suspension) was prepared. Different concentrations of this formulation, T. harzianum and Hexaconazole were evaluated for the control of dieback disease and other parameters for two seasons in three zones under field conditions. Results: The fungal antagonist (KBN-29) was identified as T. asperellum based on characteristics such as regular mycelial branching, typically paired conidiophores with straight phialides and globose to sub-globose shaped conidia. It had the maximum control of dieback pathogen in lab experiment. Spray of T. asperellum formulation at 1200 and 1000 ml/ha concentration conferred comparatively better disease control and enhanced the yield of green tea leaves. The formulation was safe to non-target beneficial insects in all three zones without any phytotoxicity to tea leaves at 4, 8, and 16ml/L concentrations.ConclusionsThe present study confirms that T. asperellum 2% AS formulation was significantly superior in managing the dieback disease of tea plantations in Darjeeling, Dooars, and Assam zones at concentration of 1200 followed by 1000 ml / ha during both seasons. The maximum made tea yield was achieved in plots treated with T. asperellum at 1200 followed 1000 ml/ha. This formulation was safe to beneficial insects viz., C. carnea, O. javanus, and S. gilvifrons, furthermore it was not phytotoxic to tea leaves at 4 to 16ml/L concentrations.