Identification of a retardant dose of glyphosate with potential for integrated control of water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach

Water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae) has a negative impact on aquatic ecosystems in South Africa. Attempts to use biological control against the weed have been hampered by low temperatures, with slow development of biocontrol agents, and excessively eutrophic waters which enable the plants to proliferate and grow at greater rates than the agents. The failure of biological control has encouraged the use of herbicides which also hinder the biocontrol agents, predominantly by destroying their food source. This study tested a broad spectrum herbicide, glyphosate, to identify whether there is a dose which will retard vegetative growth (production of ramets and leaves) but not kill the water hyacinth plants. A concentration of 0.8% achieved this goal while having no direct detrimental effects on two water hyacinth biocontrol agents, Neochetina eichhorniae and N. bruchi. The results show that application of retardant doses of herbicide might be used for integrated control of E. crassipes and this needs to be tried under natural field conditions.