Predicting damage to rice by the apple snail Pomacea canaliculata (Ampullariidae) using snail biomass
2002
Yusa, Y. | Wada, T. (National Agriculture Research Center for Kyushu Okinawa Region, Nishigoshi, Fumamoto 861-1192 (Japan))
The apple snail Pomacea canaliculata is a major pest on rice, and especially on direct-seeded rice, as the snail eats young seedlings voraciously. In southern Japan, it is advised to drain water for 7-10 days after seeding to enhance plant growth, and snail infestation does not occur during the period if the draining is perfect. However, in practice snail damage frequently occurs because fields are sometimes ill-drained and heavy rain often falls during the seeding season (early-to mid-June). Duration of submergence and growth stage of rice are important factors influencing the degree of damage, but snail density and their body size are also important. The purpose of this study is to predict damage from snail density and body size, at given rice growth stage and submergence period.Young rice seedlings (from sprouts to 5-leaf stage) were planted at 100/sq m in containers (0.2-1.2 sq m) both under the laboratory (25?) and semi-natural (no rainfall) conditions. Then 1-4 snails per sq m of various body size were released and counted the number of seedlings damaged after 1 or 2 days. At a certain leaf stage, the number of rice seedlings eaten by the snail was proportional to its body size. When the total weight of snails per sq m (biomass) was fixed, snail density did not affect the damage. These results indicate that snail biomass can predict damage to rice seedlings more accurately than snail density. In addition, damage was much smaller when seedlings were large. Duration of submergence affected damage almost proportionally. Based on these results, a dynamic threshold for snail control was proposed incorporating snail biomass and the timing and duration of submergence
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