Department of Zoology and Entomolog, Rhodes Uniersity, PO Box 94, Grahamstown 6140, South Africa
Ray, P., Department of Zoology and Entomolog, Rhodes Uniersity, PO Box 94, Grahamstown 6140, South Africa; Hill, M.P., Department of Zoology and Entomolog, Rhodes Uniersity, PO Box 94, Grahamstown 6140, South Africa
Feeding damage by arthropods is known to render water-hyacinth plants vulnerable to diseases. During this study, six South African fungal isolates (Alternaria eichhorniae Nagraj and Ponappa, A. alternata [Fr.] Keissler, Acremonium zonatum [Sawada] Gams, Fusarium oxysporum Schlecht, F. solani [Mart.] Sacc, and Myrothecium roridum Tode ex Fr) were tested for their disease-causing potential against waterhyacinth (Eichhornia crassipes [Mart.] Solms-Laubach; Pontederiaceae). They were applied to waterhyacinth in two treatments: on plants with feeding scars of weevils (Neochetina sp.; Coleoptera: Curculionidae; treatment W+) and on plants with no insect feeding damage (W-). The W+ plants were more prone to fungal infection as compared to W- waterhyacinth. A disease index (DI) of damaged plants varied significantly with different pathogens. By 45 d after treatment, DI was significantly higher in F. oxysporum (91.8 and 46.6%) and A. eichhorniae (87.6 and 65.8%) for W+ and W- waterhyacinth, respectively, followed by A. zonatum (56.6 and 50.6%), F. solani (43.6 and 27.0%), and A. alternata (26.6 and 12.6%). Lowest DI was observed in plants applied with M. roridum (21.8 and 10.0%). This study shows that to improve the biological control of waterhyacinth in South Africa, all available agents including native fungi should be released at all sites.