Trials on focal molluscicide application in larger irrigation canals and lakes in Mali

Schistosomiasis transmission in some irrigation schemes in Mali, appears to be very focal, and mainly occurs in human water contact sites close to villages. On this background, a strategy of focal snail control based on application of molluscicide to such sites only, was to be implemented in these areas. However, transmission often occurs in larger canals and lakes, and in these habitats focal snail control is obviously very difficult. This paper deals with experiments carried out to evaluate the effectiveness of focal application of 70% Bayluscide wettable powder in such habitats. Bayluscide was applied in two different ways depending on snail distribution within the sites. When snails were found in marginal vegetation, 2-3 ppm was applied along the shore (to various distances from the shore) from 10-40 m upstream from the water contact sites to 10 m downstream. In case snails were found in low submerged vegetation, which was very common in these habitats, the chemical was applied at 2-4 g (a.i.)/m2 directly between the plants. The results indicate that a satisfactory snail-kill can be achieved in the target area by this method of Bayluscide application. However, the method requires a thorough surveillance for snails and due supervision of the application. The time spacing of applications should probably be 4-6 weeks, but special situations may necessitate more frequent applications.