Decrease in density of the apple snail, Pomacea canaliculata (Lamarck) (Gastropoda: Ampullariidae) by tillage and soil puddling

Mortality of the apple snail. Pomacea canaliculata, caused by tillage or soil puddling was examined in rice fields. Tillage greatly decreased the snail density with ca. 75% mortality when the mean shell height of snails was 20.3 mm (+- 4.3;S.D.). However, "intensive tillage" using a special rotary cultivator with a smaller rotary pitch, and taking more time than ordinary tillage, had no additional effect on snail mortality. Soil puddling also attained a 67% mortality rate for snails with a mean shell height of 20.4 mm (+- 5.3;S.D.). When smaller snails (mean shell height; 11.8 +- 5.4 mm) occurred in a field. 68% mortality was attained by tillage plus soil puddling. One of the examples revealed that a density of 4.5 over wintering snails per square m in a field was finally reduced to 0.3 snails per square m by tillage plus two occasions of soil puddling. Thus, tillage and soil puddling are good methods for decreasing snail density before rice planting.