The molluscicidal properties of Ambrosia maritima L. (Compositae). 3. A comparative field trial using dry and freshly-harvested plant material.

A comparative trial of freshly-harvested and dry forms of the plant molluscicide, Ambrosia maritima is described. The plant was grown near Alexandria, Egypt and gave a weight ratio of 4:1 for fresh: dry, mature plants. Applications of plant material were made to irrigation watercourses at dosage levels of 560 mg . l-1 fresh and 70 and 140 mg . l-1 dry in May and 280 mg . l-1 fresh and 70 mg . l-1 dry in June. Snail numbers were reduced to low levels after two weeks in all treatments. Statistically significant differences could not be detected between the molluscicidal effects of fresh and dry material or their use in May and June. The cultivated plant has a similar order of activity to that collected from the wild. The snail number reduction was maintained to the end of the year in all treatments. This confirms an earlier finding that a correctly-timed, single application of the plant is capable of controlling snails throughout the entire schistosomiasis transmission season in Lower Egypt.