[Field experinence of the molluscicide "Frescon" in the control of fascioliasis (author's transl)].

The effectiveness of the molluscicide N-tritylmorpholine (Frescon, Shell) in the control of fascioliasis was tested in various field conditions. The effect was not only measured by the study of populations of L. truncatula but its use in prevention was also determined by turning tracer lambs out to grass in treated and control field. The studies showed that Frescon applied at the recommended dose rate is a reliable agent, even in the prevention of acute outbreaks of fascioliasis. The preventive effect was found to be most marked on treatment in the spring (preferable to single treatment during the summer), which is of particular importance in view of the fact that infections may occur in the southern Netherlands during the early grazing season.