Submitted to: Invasive Plants in Natural and Managed Systems Linking Science and Management in Conjuction with 7th International Conference
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2003
Publication Date: November 3, 2003
Citation: Moran, P.J. 2003. Environmental limitation on biological control of waterhyacinth. Invasive plants in natural and managed systems linking science and management in conjuction with 7th International Conference. (Abstract) Technical Abstract: Waterhyacinth (Eichhornia crassipes) is an invasive floating aquatic weed that is causing economic and environmental problems in the southeastern USA. Several introduced and native insects and plant pathogens can provide sustained biological control, but the efficacy of these agents varies greatly among field sites. Possible causes include variation in plant and water quality, interactions with other forms of weed control, and interactions among biological control agents. The importance of these factors was investigated at field sites in the Lower Rio Grande Valley of Texas and in controlled plant plots. Levels of nitrate nitrogen and phosphorous were positively associated with levels of these nutrients in leaf tissues, and were negatively correlated to plant leaf biomass and densities of waterhyacinth weevils (Neochetina spp.), which feed on waterhyacinth leaves. Field sites subjected to chemical herbicide control experienced reductions in waterhyacinth and insect densities. Regrowth populations of plants at these sites had lower damage levels and densities of biocontrol insects relative to sites at which plant populations were not disturbed by chemical control. Levels of leaf laminar damage by adult waterhyacinth weevils and necrotic spotting indicative of infection by a fungal pathogen (Cercospora piaropi) were positively associated at field sites. Prior weevil infestation led to increased necrotic spot formation after pathogen inoculation. Prior infection had no influence on leaf damage resulting from subsequent weevil infestation. Water nutrition, disturbance, and interactions between weevils and the fungal pathogen can all influence biocontrol outcomes for waterhyacinth.