VIEW ARTICLE

Disease Control and Pest Management

Biocontrol Efficacy of Cercospora rodmanii on Waterhyacinth. R. Charudattan, Professor, Department of Plant Pathology and Center for Aquatic Weeds, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611; S. B. Linda(2), Marjan Kluepfel(3), and Y. A. Osman(4). (2)(3)(4)Biological scientist, research assistant, and visiting scientist, Department of Plant Pathology and Center for Aquatic Weeds, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611. Phytopathology 75:1263-1269. Accepted for publication 28 June 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-1263.

Increased disease intensities and faster epidemic development rates of leaf spot caused by Cercospora rodmanii occurred on waterhyacinth after one application of inoculum compared to naturally occurring endemics. Leaf production on waterhyacinth was stimulated after inoculation with C. rodmanii; but, due to higher leaf mortality on inoculated plants, the net effect of disease stress was a lower number of live leaves relative to controls. The overall rate of leaf production for uninoculated and inoculated original ramets increased as nutrients increased, to a maximum at 50% Hoagland's solution and then decreased at higher nutrient concentrations (the nutrient effect was significant, P<0.01). On secondary ramets, however, the rate of leaf production increased as nutrient concentration increased (the nutrient effect was significant at P<0.01), which resulted in lower disease severity on the secondary ramets than on the original ramets and a diminution of the level of disease stress on the whole plant. On inoculated plants, lowest disease-progress rates occurred at the highest nutrient concentrations, indicating that the biocontrol efficacy of this pathogen is conditioned by the rate of leaf turnover and the compensatory host growth. For practical levels of control of waterhyacinth by C. rodmanii, the fungus should be used under conditions that favor low to moderate host growth rates or in combinations with other biotic and abiotic agents, such as insect biocontrols and sublethal rates of chemical herbicides, that retard host growth.