Instructions for preventing golden apple snails in paddy fields

Golden apple snails destroy young rice, losing seeds in the first 7-10 days of sowing. Room guidance focuses on three aspects — soil preparation, water schedule, mechanical and biological measures — instead of relying solely on drugs.

Summary: Golden apple snail is the most common early-season pest in the Mekong Delta. A heavy wave of snails can bite all the young rice overnight, losing all the sown seeds. But using too much snail crop-protection product also harms wild fish, shrimp and crab. This article guides how to prevent aggregation, prioritizing mechanical measures and water management — only use drugs when the density is too high.

Applies to: Winter-spring and summer-autumn rice crops in the Mekong Delta, crops in the Central and Northern regions. Snail destruction is strongest in areas with low-lying fields and inner-field canals.
Duration: Room from before sowing to 25-30 days after sowing.
Difficulty level: Basic. It's important to follow the basic steps correctly, don't skip them.
Estimated additional costs: 150-400 thousand VND per pole (1,000 square meters) for general room.

Characteristics and reasons why golden apple snails are dangerous

The golden apple snail (*Pomacea canaliculata*) is an alien creature introduced to Vietnam in the 1980s, initially as a pet and then escaped into the wild. Features:

Eating is very healthy. An adult eats 1-2 young rice plants every night.
Rapid reproduction — a female lays 200-500 eggs per clutch, can lay multiple clutches per season.
Eggs are laid on rice stumps, fence posts, and field edges in the form of easy-to-identify pale pink clusters.
Can live in short-term dry environments — burying oneself in mud for 3-6 months waiting for water to return.

Young rice under 25 days old is the most sensitive stage. After 25-30 days when the tree is hard, it becomes more difficult for snails to bite, but it is still affected if the density is too high.

Unlike pests that have a clear cycle, golden apple snails are continuously present in the field. If this duty is low, then the following obligations will also be low.

General room — four layers

Before sowing

[ ] Plow the soil carefully, dry it for 7-10 days before pouring water. The sun kills snails and eggs in the mud.
[ ] Harrow thoroughly and flatten the field. The low water area is where snails gather.
[ ] Collect large snails and egg clusters by hand when harrowing. It takes a little effort but it's effective.
[ ] Place the net at the mouth of the water channel into the field. Mesh mesh of 1-2 millimeters prevents snails from entering water.
[ ] Cleaning grass from field edges. Dense grass is where snails stay during the day.

When sowing and the first 7 days

This is the most critical stage. Young rice is not yet hard, snails attack the hardest.

Keep the field dry for 5-7 days after sowing. Snails need water to move and eat. Shallow fields = snails have difficulty working.
Place a small irrigation channel in the field to collect snails. Early in the morning at 5-7 o'clock, snails gather in the grooves — collected by hand.
Release ducks into the field if there are any. Ducks eat small snails and eggs very well. About 30-50 ducks per hectare is enough.
Place bait with papaya leaves and taro leaves in the evening. Early in the morning, collect bait and attached snails.

From day 7 to day 25 after sowing

Start adding water to the field gradually when the rice is 5-7 centimeters tall, hard enough to make it difficult for snails to bite.
Still continue to collect the snails by hand in the morning if the density is still high.
Ducks can continue to be released but reduce the number — many ducks trample and break rice seedlings.
Monitor the density of screws in the guide groove. More than 3-5 fish per square meter is high density, requiring stronger intervention.

After 25-30 days

The rice is hard, the snails have difficulty biting. The main thing to prevent this stage is to maintain:

Keep the field edges clean of grass.
Continue to use a net to block snails when changing water.
Watch for egg clusters on the rice base — mark by hand if you see them.

When density is high and mechanical measures are not enough

Sometimes areas with severe snail outbreaks require necessary medication. Principle:

Only spray when the snail density is above 5 snails per square meter in the first 5-7 days after sowing.
Spray locally in areas with concentrated snails, do not spray the entire field.

Recommended active ingredients (select 1 active ingredient):

Niclosamide — kills snails quickly, has little residue. Safer than metaldehyde for fish and shrimp.
Metaldehyde — common but toxic to fish and shrimp. Avoid if the field has grafted fish.
Saponin (pine seed or neem leaf extract) — biological, safest. 60-80 percent effective, needs to be repeated.

Important note: snail crop-protection products are deadly to fish, shrimp, crabs, and frogs. Areas with polyculture or near canals with natural fish should not use metaldehyde.

Monitoring the beginning of the season

[ ] Snail density in the field (snails per square meter) — counted at 3-5 points.
[ ] Proportion of rice plants bitten (count 100 plants in 5 points).
[ ] Egg clusters on rice stumps and field edges.
[ ] Effectiveness of the measures taken — how much the ducks eat, how much the treatment reduces density.
[ ] Condition of water entering the field — are there snails following the stream?

Troubleshooting

Last night the snail bit me badly, and in the morning I saw many trees bitten off:

Drain the field within 24-48 hours — the snails cannot move and will retreat to the canal.
Pluck snails by hand early in the morning.
If density remains high after drainage, use topical medication.

Ducks were released but there were still many snails:

Young ducks cannot eat large snails yet. Wait until the ducks are 2-3 months old to eat a lot of snails.
Add hands in the morning — ducks and people work in parallel.

Snails recur after thinking they're gone:

Eggs hatch after heavy rain — check the cluster of eggs on the field edge.
Water entering the field can bring new snails — check the canal gate net.

Common mistakes

Complete dependence on drugs: waste of money, harmful to the environment, snails gradually become resistant to drugs. Mechanical measures and water management are more effective in the long run.

Let the soil dry before sowing: snails and eggs are still in the mud, breaking out as soon as water is added.

Sowing immediately after plowing without flattening the field: low-lying areas that accumulate water = natural snail nests.

Do not collect egg clusters: a few seconds per cluster, discard. Skipping this step will allow the snails to produce new generations.

No coordination with neighboring households: snails move between fields along canals. A well-protected household will still suffer if the other household does nothing.

Take notes

Each case records:

Density of snails at the beginning of the season (snails per square meter).
Measures taken — how many kilograms of snails were collected, how many ducks were released, and treatment used if any.
Proportion of bitten plants after 10 days of sowing.
Yield at the end of the season.

After 2-3 crops, you will know the level of natural snails in your field, and then refine your measures.

References

*Managing golden apple snails in the field* — Plant Protection Department, 2021.
*Integrated pest management manual for rice* — Food and Agriculture Organization of the United Nations (abbreviation FAO) Vietnam, 2020.
*Recommendations for preventing golden apple snails in the Mekong Delta* — Mekong Delta Rice Institute, 2022.