RESUMO
A large-scale field trial was carried out during December 1973 to assess the effect of trifenmorph on Bulinus truncatus and Biomphalaria pfeifferi in 379 000 feddans ( approximately 159 000 ha) of the Gezira irrigation system in the Sudan. The commercial formulation used (Frescon) is an emulsifiable concentrate containing 16.5% trifenmorph. Five dispensers were used to add the commercial product to the water continuously for 7.5 days; 18 121 litres were used to treat 28.4 million m(3) of water. In addition, each minor canal was hand-sprayed from the tail to 300 m upstream of the last open field outlet pipe; 360 litres of the commercial formulation were used for this operation.A minimum concentration of 0.035 mg trifenmorph per litre of water was produced at the head of each minor canal. The use of caged snails showed that a concentration as low as 0.015 mg/litre was sufficient to produce 100% mortality in B. truncatus in 7.5 days; this is equivalent to a concentration x time product of 0.12 mg/litre days.
