Evaluation of glyphosate against weeds and phytotoxicity, productivity and soil quality parameters in tea (Camellia sinensis O. kuntze)

Glyphosate is an effective post emergence herbicide for weed control in tea. However, dose and timing of any new formulation need to be evaluated before being its recommendation to the growers. The weed flora of the experimental field was composed of Ageratum conyzoides (21.9%), Ageratum houstonianum (21.3%), Chromolaena adenophorum (13.0%), Bidens pilosa (9.6%), Lantana camara (6.2%), Cynodon dactylon (6.0%), Fragaria vesca (5.6%), Imperata cylindrica (5.2%), Polygonum alatum (5.1%) and Erigeron canadensis (5.1%). The new formulation glyphosate 71% SG was found to be comparable to the existing formulation glyphosate 41% SL against Ageratum conyzoides, A. houstonianum, Chromolaena adenophora, Bidens pilosa, Fragaria vesca, Polygonum alatum, Erigeron canadensis, Imperata cylindrica and Cynodon dactylon in reducing their population upto 120 days after application (DAA). Glyphosate 71% SG did not show any toxic symptoms on tea crop and tea leaf yield was similar as under standard formulation used in the present study. Glyphosate 71% SG (ammonium salt) sprayed at 6 kg/ha gave highest tea leaf yield (1940 kg/ha) which was statistically similar to the Glyphosate 71% SG (ammonium salt) applied at the rate of 3 kg/ha (1895 kg/ha). It was also comparable to the market sample. Uncontrolled growth of weeds even for a one season reduced tea leaf yield by 48.5%. The bulk density, water holding capacity, moisture content, soil pH, electrical conductivity, available NPK and organic C were not influenced significantly at harvest. The test herbicide glyphosate 71% SG and the market sample glyphosate 41% SL had increased the population of total bacteria, fungi and actinomycetes at harvest over their initial population. However, there was a slight decrease in the population of this microflora immediately after the application of herbicide not due to the herbicide but owing to seasonal variation as the differences between treatments were not significant.