The use of oil emulsions for improving the efficacy of Alternaria eichhorniae as a mycoherbicide for waterhyacinth (Eichhornia crassipes)

Abstract

Abstract The fungus Alternaria eichhorniae isolate #5 (Ae5) is being developed as a mycoherbicide agent for controlling waterhyacinth ( Eichhornia crassipes ) in Egypt. Inoculum concentrations above 10% (mycelial wet weight) were all equally effective in controlling waterhyacinth at 100% level (weed kill). Fresher mycelial inoculum (4 weeks old) was more virulent than older inoculum (9 or 16 weeks old). Applications of Ae5 in an aqueous carrier or in nine different oil emulsions were evaluated for the biocontrol of waterhyacinth, without a post-treatment dew period, under natural outdoor conditions. The oil emulsions were developed to provide moisture and to retard evaporation from the applied fungal inoculum so that the fungal propagules could germinate and infect the weed under relatively dry conditions. All of the invert and oil emulsion formulations induced higher levels of disease on waterhyacinth plants than the aqueous formulation under dew-free conditions. Reducing the oil content in the Ae5 emulsion formulation from 30 to 5% had no effect on the formulation’s efficacy against waterhyacinth. When applied in the winter under natural conditions in Egypt, Ae5 formulated in cottonseed oil emulsion caused 100% control of waterhyacinth in outdoor field plots 7–13 weeks after application. Thus, the results confirm the utility and feasibility of oil emulsions as formulating materials that promote the bioherbicide’s activity in the absence of dew.