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Location: Invasive Plant Research Laboratory

Title: In the Eye of the Beholder: Waterhyacinth Management in Florida

item Tipping, Philip
item Martin, Melissa
item Pokorny, Eileen
item Nimmo, Kayla
item Fitzgerald, D
item Dray, F Allen

Submitted to: Biocontrol News and Information
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2014
Publication Date: 6/5/2014
Citation: Tipping, P.W., Martin, M.R., Pokorny, E.N., Nimmo, K.R., Fitzgerald, D.L., Dray Jr, F.A. 2014. In the Eye of the Beholder: Waterhyacinth Management in Florida. Biocontrol News and Information. 35,12.

Interpretive Summary: Waterhyacinth is perhaps the world's worst floating weed and causes millions of dollars in damage to wetlands and waterways in the U.S. In Florida, herbicides are primarily used to keep weed populations at a maintenance level but this requires the perpetual application of these chemicals. Four host-specific biological control insects have been intentionally introduced to attack the plant and all are now present and feeding only on waterhyacinth in Florida. There has never been any attempt to actively integrate herbicides with these agents despite the high degree of damage they inflict on the plants. Although the insects reduced the biomass of the plants by half and virtually eliminated seed production, the coverage of the plant on the water was relatively unaffected. Most managers view biological control as ineffective and, as a result, there is little to no effort directed at actively integrating biological control with chemical control, despite the opportunities for cost savings and reduced environmental pollution.

Technical Abstract: In Florida, herbicides are the primary tactic employed to control waterhyacinth, Eichhornia crassipes with little to no consideration given to the presence of the three biological control agents introduced intentionally during the 1970's. Field research conducted at four Florida sites quantified the current levels of suppression provided by these agents. The larvae of Neochetina sp. played a major role in reducing plant biomass (r = - 0.22, n = 162, P = 0.004) and the number of inflorescences (r = - 0.27, n = 157, P = 0.0006). The biocontrol agents reduced biomass by 58.2% and reduced flowering by 97.3%. Coverage of the water's surface was relatively unaffected averaging 71.1 + 7.8 % in plots with biological control versus 85.5 + 5.6 % in plots without, a decrease of 16.8%. In most cases, coverage trended upward during the course of the experiments and was always close to 100% when the plots were harvested. Despite the relative arbitrary nature of this metric, it promotes a narrative that biological control of waterhyacinth is ineffective in Florida. Waterhyacinth populations have been significantly transformed by biological control but unless coverage can be reduced, the overall approach used to achieve maintenance control of the plant in Florida will probably not change.