Problems of golden snail infestation in rice farming
1991
Basilio, R. (International Rice Research Inst., Los Banos, Laguna (Philippines). Entomology Dept.)
The problems of golden snail infestation in rice farming systems include damage to the rice plants, rice yield losses, additional expenses, side effects of chemicals and destructive effects on native snails. The actual damage to rice crops by golden snails was first reported in 1986 from Region 2. By 1987, eight regions were infested and about 9,500 ha were damaged. This increased to about 131,000 ha in 1988, equivalent to approximately 3.6% of the total area planted to lowland rice. The most heavily infested areas were Isabela and Kalinga-Apayao in Region 2 and Occidental Mindoro in Region 4. The extent of damage to rice crops depends on snail size and population density and crop growth stage. Snails with a shell height of 6.5 cm can feed on young plants up to four weeks old. Plants at two weeks after transplanting are the most vulnerable to damage by snails. This has been shown by laboratory and field tests. Damage increases with snail density. The missing hills were 6.5% and 93% at snail population densities of 0.5 snails/sq m and 8 snails/sq m, respectively. At a density of one snail/sq m with shell height of 2-3 cm, the number of tiller may be reduced by 19% at 30 days after transplanting. This loss can be up to 98% when snail density increases to 8 snails/sq m. To avoid yield losses due to snails, farmers can retransplant but this brings additional expenses. Spot replanting of damaged hill results in non-uniform rice maturity that can also result in reduces yields and quality. Draining the ricefield is one way to control golden snail damage but this may promote the growth of weeds. Chemicals are effective against snails but most farmers cannot afford the cost. The chemicals can also be toxic to fish, frogs, and other beneficial organisms. Continuous application of chemicals decreases aquatic productivity and contaminates the environment. Some of the chemicals have adverse effects on humans working on the farms. The population of the native snail (Pila luzonica) has been reduced drastically with the increase in golden snails
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