Effect of seedling age and seedling number per hill on snail damage in irrigated rice

Rice (Oryza sativa L.) seedlings are often destroyed by golden apple snail (Pomacea canaliculata Lamarck) after transplanting. Two field experiments were conducted to determine the effects of seedling age and seedling number per hill on snail damage, plant growth. and grain yield. The first experiment was unsprayed (snail-infested experiment) while the second experiment was sprayed with molluscicide to control snails (snail-free experiment). Increasing seedling age from 2 to 5 weeks resulted in significant reductions in snail damage in terms of missing hills. Increasing seedling number per hill from 1 to 8, 6, 4, and 2 for 2, 3, 4, and 5 week-old seedlings, respectively, also reduced snail damage significantly. In the snail-free experiment, grain yield was not affected significantly when seedling age was increased from 2 to 5 weeks. Increasing seedling number per hill decreased or increased grain yield depending on the season and seedling age. In general, transplanting 4-5 week-old seedlings at one seedling per hill or increasing the number seedlings per hill reduced snail damage in terms of missing hills and minimized yield losses from the snail damage. (C) 2002 Elsevier Science Ltd. All rights reserved.