Non-target organism, Bioagent, Herbicides

Water hycienth is one of the worst weeds of water bodies in India. It is responsible for causing great loss to water by evapotranspiration besides blockage of water, loss to fish production and responsible for creating breeding sites for mosquitoes and other disease causing organisms. The host specific waterhyacinth weevils, Neochetina bruchi Hustache and N. eichhorniae Warner (Coleoptera: Curculionidae) are the most important biocontrol agents used against waterhyacinth with notable success in India. Bioagent if used alone takes longer time, hence integration of herbicide in the area of 15 to 25% of the weed mats at suitable interval is recommended. These herbicides may cause harmful effects on bioagent. Significant impact of herbicides was observed on the mortality of the weevils. When herbicide was sprayed on both the leaves and weevils, 3.3 % mortality was seen on all doses of glyphosate, paraquat and the lower (0.5x) dose of 2,4-D while higher dose (x) caused significantly high mortality of 20% by 24 hours. 2,4-D at a higher concentration caused 53% mortality followed by paraquat (50%) when herbicide was sprayed directly on weevils. Glyphosate caused the lowest mortality among the three herbicides tested