Objective To observe the molluscicidal effect and the cost of molluscicides: 25% niclosamide ethanolamine salt (SCN), 26% suspension of metaldehyde and niclosamide ethanolamine salt（MNSC）, and 50% niclosamide ethanolamine salt (WPN) used in combination with glyphosate, in order to evaluate their application value. Methods The SCN, MNSC and the glyphosate were prepared into effective doses of 2 μl/L (for laboratory immersion test), 2 ml/m3 (for field immersion test) and 2 mL/m2 (for spraying test), and the wettable powder of 50% WPN was prepared into effective doses of 2 mg/L (for laboratory immersion test), 2 g/m3 (for field immersion test) and 2 g/m2 (for laboratory and field spraying test). There were 5 experimental groups in this study: SCN, SCN in combination with glyphosate (1 : 1), MNSC, MNSC in combination with glyphosate (1 : 1), and WPN in combination with glyphosate (1 : 1). WPN was used as a drug control. Glyphosate and water control groups were also set. In the laboratory immersion experiment, 30 snails were deposited in each group, and in the field immersion test, 9 bags of snails were deposited, each containing 30 snails. At 24 h, 48 h and 72 h after drug administration, 3 bags of snails were taken back to calculate the snail death rate. In the laboratory spraying test, 100 snails were deposited in each group and the snail death rate was calculated on days 1, 3 and 7 after drug administration. In the field spraying test, a 100 m2 area of snail-containing ditch was administered with drugs, and on days 1, 3 and 7 after drug administration 10 boxes of snails were selected to calculate the snail death rate. The cost-benefit was analyzed based on the cost of molluscicides, labor cost, and herbicide labor cost. Results In the laboratory immersion experiment, the snail death rate reached 100% in all the experimental groups at 24 h, 48 h and 72 h, except for the SCN in combination with glyphosate group at 24 h, in which the death rate was 96.7% (29/30). There was no significant difference between experimental groups and the drug control group. In the laboratory spraying test, the snail death rate reached 100% in all the experimental groups on days 3 and 7, except for the SCN in combination with glyphosate group on day 1 (91.0%, 91/100) and on days 3 and 7(≥95%) at 24 h. There was no significant difference between experimental groups and the drug control group. In the laboratory immersion experiment, the snail death rate reached 100% in all the experimental groups and the drug control group at 24 h, 48 h and 72 h, except for the SCN in combination with glyphosate group (>95%). There was no significant difference between the groups (P > 0.05). In the field spraying test, the snail death rate reached 100% in MNSC in combination with glyphosate group on days 1, 3 and 7, higher than those in the drug control group (91.8%, 258/281; 95.4%, 206/216; 94.5%, 147/155) (P < 0.05). There was no significant difference between the other 4 experimental groups and the drug control group (P > 0.05). The costs of SCN, MNSC and WPN without glyphosate per 100 m2 were 101.00 Yuan, 101.80 Yuan and 103.90 Yuan due to the need of more labor input, while the costs of SCN compounding form, MNSC compounding form and WPN compounding form per 100 m2 were 69.50 Yuan, 70.30 Yuan and 72.40 Yuan, all less than the former.Conclusion On consideration of molluscicidal effect and the application cost, 2 g/m2 or 2 ml/m2 compound drugs of the three types of molluscicides are recommended in field snail control by the method of spraying.
