Biological based chemical integration for early control of water hyacinth

Water hyacinth (Eichhornia crassipes) is the most gregariously growing aquatic weed of India. An attempt was made to control water hyacinth from a village pond of about one hectare through integration of herbicides and bio-agents. One thousand bioagent weevils of Neochetina spp. were released as initial inoculation in the pond over an area of 3000 m2 for further population build up. Three herbicides namely 2,4-D (1.5 and 2.0 kg/ha), glyphosate (2.0 and 2.5 kg/ha) and paraquat (0.7 and 1.0 kg/ha) were applied in adjoining area after 15 days of bioagent inoculation in an area of 10 x30 m2 in three replicates for each dose. Population samples of water hyacinth and bioagent were taken after spray and release, respectively. On appearing new growth of water hyacinth in treated area, 15% of the total pond was again sprayed with the herbicides after 6 months. 2,4-D (2.0 kg/ha) proved the best herbicide to control water hyacinth (98.20%) followed by glyphosate 2.5 kg/ha (95.85%) and paraquat 1.0 kg/ha (93.48%). After initial control, highest regrowth was recorded in paraquat treated replications followed by 2,4-D and glyphosate. Population sampling of bioagants revealed spread and increase in number of the weevil in the entire pond. Bioagents also invaded re-growth rapidly resulted after herbicide spray. Neochetina spp. adult population was found increased in the adjoining area treated with herbicides. After 9 months of biological and chemical integration, the first cycle of complete control was achieved. This early collapse of weed within a period of 9 month could be possible due to integration of herbicide and bioagents which would otherwise have taken minimum 24_36 month by the bioagents alone. After some time, again water hyacienth population increased due to new germination from buried seeds or from the left stolons of water hyacinth. This second wave of water hyacinth was again collapsed in 21 months due to integration of one spray of herbicides after one month of regrowth.