UPASI Tea Research Institute, Nirar Dam BPO., Valparal Coimbatore District, Tamil Nadu, India 842 127

Background and objectives
Blister blight incited by Exobasidium vexans Massee is the most important leaf disease affecting both the quality and productivity of tea. The pathogen infects only the economically important, tender shoots which leads to enormous crop loss, estimated upto 50% depending on the severity of infection. In order to generate information on triazoles against the blister blight pathogen, the present study was carried out at UPASI Tea Research Institute., Valparal, India.

Materials and methods
Conventional and third generation fungicides including triazoles were evaluated for their fungitoxic property in replicated field trials using blister susceptible seedling teas. A microplot trial has also been conducted between 1995 and 1997 to generate information on phytotonic effect of triazoles in clonal tea, UPASI-3. The treatments were imposed with air blast spraying machines with a spray volume of 70 l/ha covering two rows of tea bushes on either side. The triazoles, bitertanol (Baycor 25 WP at 200 glha) and propiconazole ~lt 25 EC at 250 mi/ha) were tried besides the conventional fungicides, copper oxychloride and nickel chloride, 210 g each/ha, as standard. Standard procedures were adopted for physiological and biochemical parameters.

Results and conclusions
Laboratory studies revealed that, at 2 ppm concentration, pmpiconazole and bitertanol suppressed the germination of basidiospores and the per cent inhibition was 70 and 45, respectively. Under field conditions, bitertanol and propiconazole were equally effective in controlling the disease [1]. The protection achieved was 68% as against 78% in standard. However, the triazoles recorded about 6% crop increase over the standard. The suppressive effect of triazole fungicides on spore formation and their germination have already been studied extensively.
Results on microplot trial revealed that triazoles had enhanced the photosynthetic rate, significantly. Radioactive carbon isotope studies confirm the enhanced photosynthetic rate and the increased mobilization of assimilates towards growing shoots. The increase was 7.6% and 7.3% in response to bitertanol and propiconazole, respectively. Triazoles have an edge over the conventional standard in certain biochemical constituents like chlorophyll, amino acids and proteins which are responsible for metabolic functions and quality of commercial black tea. The increase obtained was 5%, 13% and 3% in total chlorophyll, amino acids and protein, respectively, overthe standard. The results obtained in the present study confirm the earlier st~dy on growth regulating properties of triazoles [2]. HPLC analysis of bitertanol applied leaf samples indicate that two to four hour rain-free period is adequate for about 60% of absorption.
Based on the data obtained, spray schedules on these chemicals were recommended to the south Indian tea plantations for adoption. Triazole schedules are advantageous because of their low active ingredient and longer residual action which enables cost effective blister blight management in tea.

1. Premkumar R, Baby UI, 1998. UPASI Sci. Bull. 49: 47-54.
2. Fletcher RA, Hofstra G, GaOJG, 1986. Plant Cell Physiol. 27: 367-371.