In-water activity of glyphosate, 2,4-D, and diquat on waterhyacinth (Eichhornia crassipes)

Waterhyacinth is an aggressive floating macrophyte that has been traditionally managed using foliar applications of 2,4-D and diquat. Recent research suggests that 20-25% of herbicide is lost to the water column. Here we evaluate the relative efficacy of subsurface applications of 2,4-D, diquat, and glyphosate to determine if spray loss from foliar applications provides additional efficacy through absorption from roots and submersed leaves. Plants were established in mesocosms and treated with diquat at rates of 100, 200, 400, 800, 1600, or 3200 lg L-1. Both 2,4-D and glyphosate were applied at rates of 125, 250, 500, 1000, 2000, 4000, or 8000 lg L-1. Total plant biomass was harvested after 28 days of static exposure. Results suggest that subsurface diquat applications are effective at water hyacinth control, with total plant death observed at 3200 lg L-1 and biomass reductions of 92% at 1600 lg L-1. Neither 2,4-D or glyphosate was effective at reducing waterhyacinth biomass regardless of application rate. Results suggest that spray loss from glyphosate and 2,4-D applications represents wasted product and cost, whereas spray loss from diquat may provide additional efficacy on waterhyacinth.