Use of a plant molluscicide, Apodytes dimidiata, in a preliminary field trial in KwaZulu-Natal, South Africa

A preliminary field trial was carried out in KwaZulu-Natal, to evaluate the molluscicidal efficacy of Apodytes dimidiata under local conditions. Molluscicidal concentrations (LD90) were focally applied over a four-month period to a site on the Umhlanga River north of Durban. Results suggested that the plant had a limited effect in reducing snail numbers. However it is probable that abnormal flooding of the river during the trial masked its true efficacy, giving exaggerated results. Seasonal and ontogenetic variations in molluscicidal potency of the leaves, collected during the second harvest, resulted in an g-fold decrease in the material's efficacy. Consequently, large quantities of crude plant material had to be collected to obtain the LD90 dosage as determined in the laboratory. We conclude that low and unpredictable potency levels of A. dimidiata negate the use of this plant in self-help snail control programmes in South Africa. Even though the plant failed to meet the necessary criteria for effective snail control, useful experience was gained in the application of plant molluscicides to natural waterbodies.