Evaluation of different duck varieties for the control of the golden apple snail (Pomacea canaliculata) in transplanted and direct seeded rice

This study investigated the potential of ducks for the control of the golden apple snail in irrigated rice. The varieties of duck recommended for the biological control of snail in decreasing preference were William Siam > Taiwan > Mallard > Peking > Muscovy. Cherry Valley, a variety with a bigger body size was not suitable for snail control because of its poor adaptation to rice field conditions. A density of 5-10 ducks ha(-1) in continuous grazing for a period of 1-2 months significantly reduced the pest density from 5 snails m(-2) to less than 1 snail m(-2). This density of ducks was recommended for biological control of snails in rice. Timely release of ducks was crucial as they damaged young rice seedlings. In transplanted rice, it was appropriate to release the ducks when the seedlings were 4 weeks old. For direct seeded rice, a longer waiting period of 6 weeks was necessary. Numerically, ducks preyed on more snails in transplanted than in direct seeded rice, but the difference was not statistically significant. The increase in plant density under direct seeding probably reduced the browsing efficiency of the ducks. This difference would be expected to diminish under prolonged grazing. It is suggested that ducks were an effective biological control agent against the golden apple snail. (C) 2001 Elsevier Science Ltd. All rights reserved.