Objective: To investigate the distribution of snails in a nursery stock park in the middle region of Zhejiang Province and assess the risk of snail output via the mud balls of transplanted seedlings, to provide scientific data for making strategies for snail control.
Methods: We selected three species of seedlings including Osmanthus fragrans (a large tree), Camellia sasanqua (a small tree), and Purpus privet (a type of shrub) in a nursery stock park in a snail-positive middle region of Zhejiang Province during 2014-2016 to calculate the areas of regions with snails and the density of living snails. In 30 trees of each species, the distribution of snails within the seedlings ground diameter (radius of investigation, 100 cm for Osmanthus fragrans; 30 cm for Camellia Sasanqua and Purpus Privet) and in different soil layers (surface and superficial layers, 0-3 cm; deep layer, 3-10 cm) was assessed. In addition, the presence of snails in mud balls of 50 trees of Photinia fraseri (a small tree with high density of snails) was investigated to assess the risk of snail output.
Results: In the planting areas of Osmanthus fragrans（3 930 m2）, Camellia sasanqua（2 000 m2）, and Purpus privet （1 700 m2）, the areas of snail-positive regions were 200, 900 and 800 m2, respectively, with the density of living snails being 0.08, 0.56 and 0.55/0.1 m2. For Osmanthus fragrans, Camellia sasanqua and Purpus privet, 238, 654 and 645 snails were detected respectively within their seedlings ground diameter, including 159（66.8%）, 461（70.5%） and 376 （58.3%） snails in the surface layer, respectively, which were significantly higher than those in the superficial and deep layers（P＜0.01）. Snails were found in all the 50 trees of Photinia fraseri（3 726 snails, 706 adult snails and 3 020 immature snails, 75 snails/tree on average）.
Conclusion: There is a high density of snails in the nursery stock park in the middle region of Zhejiang Province. The snails are distributed mainly in the surface layer, suggesting a risk of snail output through mud balls.