A case study of waterhyacinth (Eichhornia crassipes) control in Puerto Rico using glyphosate and hand removal

Abstract

Waterhyacinth is an aquatic invasive plant that is widespread in Puerto Rico where it negatively effects estuaries, freshwater wetlands, potable water reservoirs, and wildlife refuges. Specifically, the tropical estuary San Juan Bay Estuary (SJBE) has been impacted with the presence of waterhyacinth. Infestations have led to a reduction of water circulation in the system as well as facilitating the establishment of invasive fauna. Therefore, a field study was conducted in a cove between Laguna San Jose and Peninsula Cantera to assess the use of glyphosate and hand removal as a management tool for waterhyacinth control. Aquatic macroinvertebrates and water quality were also monitored as a measure of environmental impact due to management activities. Results indicated that two weeks after glyphosate application, waterhyacinth biomass was significantly reduced to 0.27 kg DW m−2 at the treated plot as compared to untreated plot that yielded 0.62 kg DW m−2. Fresh weight of waterhyacinth decreased more than 90% when hand removal was used as compared to glyphosate treatment. Dissolved oxygen and water pH were not significantly different between sites however, water salinity increased to 8-9 ppt at both plots caused by tidal activity. The order Hemiptera followed by Sarcoptiformes were common at the aquatic macroinvertebrate community. Macroinvertebrate species found associated with waterhyacinth and considered natural enemies were: Orthogalumna terebrantis, Neochetina eichhorniae, Niphograpta albiguttalis. The use of glyphosate to manage waterhyacinth at the Laguna San Jose was useful as a short-term control method and its efficacy may be enhanced over time with follow up applications in combination with hand removal.