Instructions for preventing rice shell borers

The rice sheath borer damages rice from seedlings to tillers. The larvae cut leaves to create floats on the water surface and then crawl up at night to bite and destroy. Instructions on identifying ladder damage, draining water and properly disposing of medication.

Summary: Rice caseworms often appear from the seedling to tillering stage, especially in continuously flooded fields. Larvae cut leaves and roll them into "floats", during the day they float on the water surface, and at night crawl up rice plants to scrape leaves. This article provides instructions on correctly identifying float worms, draining water promptly and using medication when needed without causing an outbreak of hoppers.

Applies to: paddy fields sown or transplanted in the Mekong Delta, Central and Northern regions, especially fields with deep water at the beginning of the season.
Duration: Monitor from seedling to end of tillering.
Difficulty level: Basic. It is important to see the leaf float on the water surface and treat the water before spraying.
Estimated additional costs: 150-400 thousand VND per acre if spraying is required; lower if treated early with water management.

How harmful is the shell borer

The float worm appears early in the rice crop. Adults are small butterflies, with bodies about 5 millimeters long, bright white, wings with black and light brown spots.

The larvae cause harm in a rather special way:

Newly hatched larvae feed on the surface of young leaves.
When they get older, the worms bite off the leaves.
Bitten leaves are rolled up into floats on the water.
Deep inside the buoy during the day.
At night, the worm crawls up the rice plant to scrape the leaves and sheaths.

The damage often leaves white cuticles on the leaves, looking like small steps.

Identification signs

Go to the fields in the early morning or late afternoon:

See many pieces of rolled leaves floating on the water surface.
Open the leaf float and you can see deep inside.
Young leaves are scraped and have white streaks.
The rice seedlings lost their leaves and developed slowly.
Fields with deep water are often more severely affected than fields with medium water.

Float worms are easily confused with leaf rollers, but leaf rollers usually roll leaves on plants, while float worms have "floats" that float on the water surface.

Deep growing conditions

Floor worms often thrive when:

The fields are continuously flooded.
The water level is deep during the young rice stage.
Transplanting young seedlings.
The field has a lot of grass and plant residue.
The rice is still weak, tillering is not strong yet.

Water management is key. If the fields are always flooded, the depths have a favorable environment for making buoys and moving.

Water management measures

When worms are detected:

Drain the field in 1-2 days if conditions allow.
Collect floating leaves floating in the wind or in the gutter.
Collect buoys and destroy them.
After the pests are reduced, bring the water back to a shallow level suitable for the age of the rice.

Withdrawing water causes the worm to lose its buoyancy and movement environment. This is a step you should do before thinking about treatment.

When to spray

Consider spraying when:

High worm density, many leaf floats.
The rice is still small and has obvious missing leaves.
After draining the water, the worms still cause harm.
The field is in the seedling stage — branching, needs to maintain bud density.

Do not spray if you only see a few floats and the rice plants still recover well.

Choose treatment and spray technique

Floor worms are quite sensitive to crop-protection products. Active ingredients are usually used according to labels and local recommendations:

Abamectin.
Emamectin benzoate.
Azadirachtin.
Other biologically active or selected ingredients suitable for rice.

Technology:

Drain water before spraying if the field is deeply flooded.
Spray in the cool afternoon.
Spray evenly on the lower leaves and the field surface where the float is located.
Do not spray before rain.
After spraying, slowly add water again for 1-2 days.

Do not use synthetic pyrethroids if not absolutely necessary because it can cause brown planthoppers to break out later.

Room from the beginning of the season

Create the land and level the fields.
Do not keep deep water for a long time when the rice is young.
Clean the grass banks and grass in the fields.
Sowing or transplanting at the right density helps plants stay healthy.
Do not spray crop-protection products early if the threshold has not been exceeded.

Fields with good water management often have fewer floods than fields that are continuously flooded.

Monitor periodically

[ ] Number of leaf floats per square meter.
[ ] Proportion of trees with leaves scraped.
[ ] Field water level.
[ ] Rice stage: seedlings, early tillering or full tillering.
[ ] Are there brown planthoppers or natural enemies in the field?

If worms appear after rain or after holding deep water, you need to review the water schedule.

Common mistakes

Only spray, do not drain water: the worms still reside in the float, reducing effectiveness.

Keeping fields deeply flooded at the beginning of the season: creates conditions for worms to grow.

Confusing float worms with leaf rollers: handled at the wrong time and in the wrong place.

Using synthetic chrysanthemum drugs indiscriminately: easily causes bedbug outbreaks.

Do not collect leaf floats: the floats still have live worms, continuing to cause harm.

Take notes

Date of discovery of buoy worms.
Field water level at time of discovery.
Number of leaf floats per square meter.
Measures taken: water withdrawal, buoy collection, spraying.
Results after 3-5 days.

Taking notes helps you know which fields are prone to deep water retention or sunken field surfaces.

References

*Guidelines for preventing shellfish borers* — Hainong technical document.
*Integrated pest management for rice* — Plant Protection Department.
*Rice IPM Handbook* — FAO Vietnam.