Why Golden Apple Snails Cannot Be Eaten, What Harm They Cause, and How to Control Them, with Farming Techniques Included
The Golden Apple Snail, also called the large apple snail or apple snail, looks extremely similar to the river snail, with a large body, broad diet, strong adaptability, fast growth and reproduction, and high yield.So why can't Golden Apple Snails be eaten? What harm do they cause? How are they controlled? What farming techniques are there?According to Mr. Wang, a restaurant owner in Changsha, the flesh of the Golden Apple Snail is edible, but the texture is poor, and eating Golden Apple Snails that have not been thoroughly heated may cause parasites such as Angiostrongylus cantonensis to infect the human body.
What harm do Golden Apple Snails cause?
1. Golden Apple Snails have a large appetite and eat a wide variety of foods, and can damage the growth of grain crops, vegetables and aquatic crops.
2. Golden Apple Snails have mixed feeding habits and harm lotus roots. Young snails can gnaw from the underside of leaves on lotus leaves floating on the water surface, causing holes or notches in the leaves; in severe cases the leaves are eaten full of holes and find it hard to rise above the water surface. Golden Apple Snails also harm various aquatic plants such as narcissus and orchids, and have become a major pest in the waters of southern China.
3. The Golden Apple Snail is also an intermediate host of a zoonotic parasitic disease, and can very easily bring health problems to nearby residents.
How are Golden Apple Snails controlled?
1. Agricultural measures
① Eliminate overwintering snail sources. Golden Apple Snails mainly overwinter in streams, rivers, canals and low-lying waterlogged ditches, so before spring ploughing the ditches beside rice fields should be cleared, silt and weeds removed, and the overwintering sites of Golden Apple Snails destroyed to reduce the survival rate of overwintering snails and the number of remaining snails after winter. At the same time, chemical control should be used for ditches and low-lying waterlogged areas.
② Block transmission: in downstream areas of heavily affected regions, install barrier nets at irrigation canal entrances or rice field water inlets to prevent Golden Apple Snails from entering the fields with the water.
③ Manual capture and killing: during the spring peak egg-laying period, combine field management with removing egg masses from fields and ditch edges, carry them away from the rice fields to feed ducks, or crush the egg masses. When fields are dried, adult snails mainly gather at water inlet and outlet openings and in seedling field ditches, so collect snails by hand in the morning and afternoon. Manually remove egg masses and collect adult snails in conjunction with farming activities. When fields are dried, adult snails mainly gather at water inlet and outlet openings and in seedling field ditches, and manual collection can also control the damage.
④ Manual trapping and killing: after the rice field is flooded, insert bamboo strips (wooden sticks, rapeseed straw) 30-100 cm high into the rice field to attract Golden Apple Snails to lay eggs concentrated on the bamboo strips (wooden sticks, straw), and remove and destroy the egg masses once every 2-3 days. The quantity should be 30-80 bamboo strips (wooden sticks, straw) per mu, with appropriately more inserted near the field edges to make egg mass removal convenient.
2. Biological control
Biological control mainly uses ducks to eat the snails. The duck release period is from 7-10 days after rice transplanting to the late booting stage of rice. Each morning and at around five or six o'clock in the afternoon, release ducks (15-30 per mu) into rice fields and canals to peck at young snails, reducing snail numbers and damage.
3. Chemical control
① Control thresholds: during the rice seedling stage, 1-2 snails per sq m, 1 egg mass per sq m at field edges; during the tillering stage, 3-4 snails per sq m, 1-2 egg masses per sq m.
② Control agents: 10% Woju granules, 6% Mida molluscicide granules, 50% niclosamide ethanolamine salt wettable powder, 70% niclosamide wettable powder, 45% triphenyltin acetate wettable powder, etc.
③ Application timing: two applications: 1. Apply at the 2-leaf 1-heart stage of rice in the seedling field. 2. Apply at transplanting. If snail damage is severe, apply once more after 10 days.
④ Application method: 10% Woju granules at about 400-500 grams per mu, evenly broadcast in the field or mixed with 5-10 kg of fine soil and broadcast. 6% Mida molluscicide granules at about 400-550 grams per mu, evenly broadcast in the field or mixed with 5-10 kg of fine soil and broadcast. 70% niclosamide ethanolamine salt wettable powder at 60 grams per mu, diluted with 20 kg of water and sprayed.
4. Precautions: when applying, the field water layer should be 1-3 cm, and water should be retained for 7 days. If heavy rain falls within 24 hours after application, one supplementary application is needed. Molluscicides are toxic to fish; within 7 days after application, field water must not be drained into fish ponds, and ducks must not be released.
Appendix: Golden Apple Snail farming techniques
Golden Apple Snails are feed for some valuable aquatic animals, and farming them can provide live bait for aquatic animals.
1. Choose a suitable farming environment. Golden Apple Snails require fresh water quality, so the farming water surface should have convenient drainage and irrigation, with a water depth of 0.3-1 m being suitable. A large area can be 3-5 mu, while a small one can be just a few sq m. Aquatic plants should be planted in the farming water surface to provide the snails with an environment for escaping heat and light and for perching, while also providing natural feed. Generally, the density of aquatic plants can occupy 30%-35% of the water surface. To facilitate feeding and management, bamboo poles can be used to divide the water surface into several sections. In adult snail ponds, insert more bamboo and wooden strips to provide egg-laying sites for female snails. Carp, tilapia and soft-shelled turtles all eat young snails, so some silver carp fingerlings can be stocked; therefore, before releasing snails, drugs should be used to eliminate pests. Water inlets and outlets should be blocked with fine-mesh nets to prevent snails from drifting away with the water.
2. Snail stocking. Stocking density should be determined according to water source, feed, management conditions, and the size of seedlings and planned harvest specifications. Generally, about 5,000 newly hatched young snails can be released per sq m; when they grow to about 3 g at 20 d, they can be thinned to about 2,000; afterwards they can be further thinned as the snails grow; or they can be stocked all at once and gradually harvested large while leaving small as individuals grow. Snails of different sizes have different feeding abilities, and where conditions permit, snails of different sizes should be raised separately so that they feed evenly and grow in sync.
3. Feed provision. The total daily feed amount is generally about 10% of the total snail weight, of which concentrated feed is more than 0.5% of the total snail body weight, while green feed is determined by the need to satisfy their feeding. Feed should be fresh and not spoiled or deteriorated. When green feed and concentrated feed are fed at the same time, green feed can be fed first, and once it is basically eaten up, concentrated feed can then be fed. Golden Apple Snails avoid direct light; during the day they sink to the bottom or hide in dark places, and at night they float to the water surface to move and feed. Therefore, feeding should be carried out in the evening.
4. Water quality management. Golden Apple Snails eat a large amount and produce a lot of excrement, and pond water easily spoils and deteriorates, so water quality management is very important. To ensure the snails can continue to grow quickly, water should be changed frequently to keep the water quality fresh. When water quality deteriorates, snails grow more slowly or even die. Where conditions permit, keeping the farming water body with slight water flow gives the best effect. In static water farming, change the water about once every 7 d.
5. Centralized egg mass hatching. The method is to set up a bamboo mat (with many small holes) horizontally 20-30 cm above the water surface of the hatching pond (or young snail rearing pond), and spread the egg masses flat on the mat. Cover the egg masses with shade material (such as tree branches, etc.) to prevent exposure to strong sunlight. After hatching, the young snails fall into the water and begin feeding and growing.
6. Eliminate pests and prevent escape. Rats and yellow weasels cause relatively serious harm to Golden Apple Snails, and rats are especially good at eating snails near the water, so measures should be taken to guard against them. At the same time, the firmness of the fine barriers set at water inlets and outlets should be checked at any time to prevent snails from leaving with the water.