Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/2/2005
Publication Date: 8/2/2005
Citation: Moran, P.J. 2005. Water nutrients, plant nutrients, and indicators of biological control in waterhyacinth at Texas field sites. Aquatic Plant Management Society Meeting. p. 39.
Technical Abstract: Interactions occur under controlled conditions between the nutrient content of floating waterhyacinth plants (Eichhornia crassipes) and reporduction of waterhyacinth weevils (Neochetina bruchi and N. eichhorniae) introduced for biocontrol. Few studies have linked water nutrition, plant nutrition, and biocontrol meaures in waterhyacinth under variable field conditions. Fifteen sites in coastal Texas were sampled repeatedly in 2003 and 2004. Water samples were analyzed for total nitrogen and reactive phosphorous. Plant biomass, damage by waterhyacinth weevils, symptoms of a fungal plant pathogen (Cercospora piaropi), and leaf nitrogen (N) and phosphorous (P) contents were determined. Total water nitrogen concentration was strongly, positively, correlated to leaf N and P. Water phosphorous concentrations were more modestly associated with leaf N and P. Water collected from five sites on the Lower Rio Grande had higher nitrogen and phosphorous levels than did water from four South Texas sites off of the river. Chemical and mechanical removal of waterhyacinth from the Rio Grande in 2003 did not substantially alter water nutrient differences between on- and off-river sites. In 2004, sites with flowing water (the Rio Grande and irrigation canals) had near-significantly more water and plant tissue nitrogen than did sites with relatively low-flowing water (ponds, reservoirs), and plants growing in flowing water had more biomass. Damage by waterhyacinth weevils and leaf coverage by C. piaropi necrotic spots were higher at low-flow sites, and necrosis was negatively correlated to water and plant N levels. Water nutrients could alter biological control efficacy by influencing plant nutrient levels and plant biomass.