Strategies for Controlling the Apple Snail Pomacea canaliculata (Lamarck) (Gastropoda: Ampullariidae) in Japanese Direct-Sown Paddy Fields

Abstract

The apple snail Pomacea canaliculata becomes a much more serious pest in direct-sown rice fields than in transplanted fields. In south Japan, it represents an important constraint on the implementation of direct seeding. Described here are possible measures to control the snails and suggestions for its management in Japanese direct-sown rice fields. Crop rotation with upland crops is a practical way with the lowest extra cost. The apple snails were often not eradicated by growing an upland crop in the previous summer. However, snail densities always decreased below the control threshold in direct-sown fields (0.5 snails/m 2 ). Longer drainage period after sowing greatly reduced snail damage. Thus, draining fields for 10 to 20 days after sowing is a basic practice to control snails in direct seeding. Tillage and puddling have a function to crush snails and, thus, reduce snail densities. Intensive tillage, in which a field with compacted hard soil is tilled shallow with faster cultivator rotation, achieved higher snail mortality. It is recommended to lower the risk of snail damage after unexpected heavy rain. An application of bait type metaldehyde showed enough control effects to avoid rice damage by snails even in heavy rain conditions. The stable effects seemed to be due to the active ingredient in the bait type which is dissolved slowly. Improving techniques for weeding and for draining fields effectively are necessary for better snail management in direct seeding.