Abstract
In the Gezira Irrigated Area of the Sudan the results from a series of applications of the molluscicide N-trityl morpholine were used to propose a regimen for snail control. The regimen aims at reducing the snail population by at least 95% (and usually more) of the population levels in untreated canals, to reduce the transmission of schistosomiasis. Drip-feed application of N-trityl morpholine (Frescon) to a pilot area of the Gezira irrigation network failed except during Sept.-Dec. At that time water requirements were maximal but the molluscicide coverage of the system was incomplete so that each drip-feed had to be supplemented by knapsack spraying of minor canal tail ends. This was tedious and difficult. Aerial spraying was the most effective, least troublesome, quickest and cheapest application technique. Using this method blanket coverage of the whole network of canals is logistically feasible. The effectiveness of the regimen in achieving reduction of transmission and the cost effectiveness of other methods must be considered before larger scale snail control is implemented.

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