Effect of drainage on damage to direct-sown rice by the apple snail Pomacea canaliculata (Lamarck) (Gastropoda : Ampullariidae)

抄録

Damage to direct-sown rice by th apple snail, Pomacea canaliculata, was investigated in two semi-field experiments using rain-free experimental plots (each 2 m² in area). Four snails (2 snails/m²), with shell heights of approximately 19 mm or 24 mm, were released in the plots at the time of sowing When the plots were irrigated soon after sowing (0 or 4 days after sowing), the snails fed avidly on young seedlings and no plants became established Drainage after sowing greatly reduced snail damage. Eighty seven to 94% of plants as compared to the control plots without snails were established when plots were drained for two weeks. Three weeks of drainage could almost prevent damage by snails (95-99% of plant establishment) when the plant age was at about the 5.0 leaf stage. Snail damage was more severe when herbicide was applied. Water management after sowing in direct-seeded rice is discussed in view of reducing snail damage.