Attempts to eradicate snails from impounded water by the use of N-tritylmorpholine

This paper records attempts to overcome the problems of using a powerful but non-ovicidal molluscicide (N-tritylmorpholine) in eradicating snails from a dam by treating the water twice in 14 days. The first treatment was aimed at the existing snail population and the second at snails hatched from eggs that survived the first application. At each treatment an over-all concentration of 0.25 ppm was applied by spraying a 16% emulsifiable concentrate of N-tritylmorpholine from shore and boat to the water surface. The snails, Biomphalaria pfeifferi and Lymnaea natalensis, were first seen again 8 weeks from the start of the application in the region of 2 inlet furrows. When pretreatment levels of snails were again reached, a second double treatment was applied, again at an over-all concentration of 0.25 ppm but using a 50% paste formulation applied over 3 days for 3 hours per day to the inlet furrows. The snail kill was again 100% as measured by the sampling technique used but again young snails appeared 9 weeks later. The author concludes that single treatments at 5-week intervals probably represent the best means of control with N-tritylmorpholine.