Innundative biocontrol of water hyacinth (Eichhornia crassipes (Mart.) Solms. Laubach) using zonate leaf spot (Acremonium zonatum Sawada Gams) fungal agent

Abstract

Innundative (tactical, bioherbicidal or mycoherbicidal) approach of biocontrol involves culturing spore inoculum in artificial media, harvesting, concentrating and formulating it in order to withstand storage and handling so that it can be applied to the weed in the same way as a chemical herbicide. A trial was set up in Maseno University green house to test the effect of concentrating and formulating A. zonatum spores in vegetable oil, mineral oil, pure commercial grade glycerol and tween 80 for use in water hyacinth biocontrol. Acremonium zonatum was isolated from infected plants collected from Winam gulf of Lake Victoria. The isolates were cultured on PDA under aseptic conditions. Microscopy, Olga's Identification keys and Koch's Postulate were used to identify the isolates. The isolates were multiplied on several PDA plates and spores harvested when mature. Using a counting chamber, the spores were concentrated into four levels; 10 5 , 10 6 , 10 7 and 10 8 spores/ml and formulated in mineral oil, corn oil, tween 80 and glycerol. Healthy water hyacinth plants with five fully expanded leaves were collected from Winam gulf, placed in 7.5 cm diameter plastic basins and taken to the green house to acclimatize for 4 days. The plants were injured and inoculated. They were set up in a RCBD experiment within the glasshouse. Data on disease incidence was collected and analyzed using excel's QI Macros 2013 version statistical package. The results showed that concentrating and formulating A. zonatum in oil emulsion makes it possible for the pathogen to be used innundatively as a mycoherbicide against water hyacinth. There was extensive leaf infection but new leaves continued to form, an indication that A.zonatum formulated in oil emulsion can be used in the control of water hyacinth but in an integrated approach with other control methods.