Influence of unrefined corn oil and surface-active agents on the germination and infectivity of Alternaria helianthi

A dew immediately after inoculation is normally required for the mycoherbicidal activity of Alternaria helianthi on common cocklebur. The formulation of A. helianthi conidia in an emulsion of unrefined corn oil enabled the pathogen to infect the weed, regardless of whether dew was immediate or delayed for 24 h. Corn oil emulsion and the surface-active agents Tween 20, 40, 60 and 80 maintained the germination ability of 14-day-old conidia to some degree for up to 4 days in suspension. Both the corn oil emulsion and Silwet stimulated the germination of A. helianthi on common cocklebur leaves, but Silwet did not enhance infectivity when dew was delayed. Unrefined corn oil enhanced mycoherbicide efficacy by protecting the conidia during a dew-free period and by stimulating germination when a dew occurred, Corn oil emulsion, Silwet and Tween 20, 40, 60 and 80 reduced the dew period required for disease activity. Unrefined corn oil emulsion has potential as a formulation for the application of this mycoherbicide in the field because it maintained the germination ability and virulence of conidia oil the weed during a dew-free period.