Instructions for preventing two-spotted rice stem borers

The two-spotted rice stem borer causes dead buds in the growth stage and silvery flowers when rice blooms. Instructions on identifying egg nests, treatment thresholds above 2 egg nests/m2 and how to prevent them by sparse sowing, balanced nitrogen fertilization, and timely field visits.

Summary: The two-spotted rice stem borer can cause damage from seedling to maturity. In the early stages, worms kill the buds; During the flowering stage, worms produce silver flowers and flat seeds. The important point is to check the egg nests and butterflies during the blooming stage until the end of flowering, because once the worms have entered the body, spraying is difficult to be effective.

Applies to: paddy fields in areas where stem borers appear every crop, especially fields sown thickly, with excess nitrogen fertilization or late sowing.
Duration: Monitor from tillering to flowering, most important before and during the flowering stage.
Difficulty level: Medium. You need to check the eggs, not just the silver flowers.
Estimated additional costs: 250-600 thousand VND per pole if handled properly.

How harmful is the two-spotted rice stem borer

Adult butterflies lay eggs on the tips of rice leaves. The eggs are often covered with fluff. When the eggs hatch:

The larva burrows into the rice stem.
During the growth stage, the caterpillar destroys the growth tip, causing the bud to die.
During the flowering stage, cotton worms cannot feed the seeds, creating silver flowers.
The worm is located in the body so it is difficult for the treatment to reach if treated late.

This is the reason why stem borer prevention must rely on monitoring egg nests and when new worms hatch.

Identification signs

Deadhead

At the seedling — tillering stage:

The middle bud withers, turns yellow and dies.
Gently pull the bud and it can be pulled out easily.
The base has holes or deep segments.

However, during the seedling stage there is usually no need to spray if the population is low, because the plant still has the ability to branch out to compensate.

Silver

At the flowering stage:

The rice is silvery white, not sure.
The cotton stands upright, not bowed like healthy cotton.
Flat seeds or no seeds.
Cut the stem and you may see worms or chiseled lines.

Once you see a lot of silver flowers, the damage is almost done. Need room sooner.

Egg nest

Usually located on the tip of the leaf.
There is a layer of down.
If the egg nest density is high, the risk of larvae hatching and boring into the stem is very high.

Checking the nest is a better way to make decisions than waiting to see silver flowers.

Deep growing conditions

Stem borers are often worse when:

Thick sowing.
Excess nitrogen fertilization.
The seeding of the fields is late compared to the region.
There are many stages of rice around the area.
After harvest, there are still a lot of stubble and broken rice.

Mass sowing and field cleaning help cut the life cycle of pests better than single spraying.

Processing threshold

There is no need to spray stem borer insecticide at the seedling stage if the population is low and the plant is still capable of recovery.

Need to consider treatment when:

There are more than 2 egg nests per square meter.
The stage of rice from early flowering to the end of flowering.
The field has a history of heavy cotton.
Butterflies appear in abundance and eggs are hatching.

How to check:

Choose 5 points in the field.
Each test point is 1 square meter.
Count the eggs on the leaves.
Add the proportion of silver flowers if they have bloomed.

Prevention by farming

Sow sparsely, sow simultaneously

Sow at reasonable density according to variety.
Sown with the same regional schedule.
Avoid late sowing seeds to make the field a place where pests gather.

Apply balanced fertilizer

Do not fertilize with excess nitrogen.
Increases potassium during tillering and flowering stages.
Do not apply nitrogen late when the field already has worms.

Dense green rice with soft stems is a favorable environment for worms.

Post-harvest cleaning

Plowing and burying stubble.
Kill rice.
Cleaning field edges.
Cut the crop if the area has high deep pressure.

The stubble and rice stubble are where worms exist between crops.

Spray when necessary

Active ingredients are usually used according to the label and local recommendations:

Chlorantraniliprole.
Emamectin benzoate.
Carbosulfan or other suitable active ingredient according to registration.

Spraying technique:

Spray when eggs are about to hatch or larvae have just hatched.
Spray in the cool afternoon.
Spray enough water so that the treatment reaches the sheath and stem.
Do not spray when the worms have burrowed deep into the stem and there are no new eggs left.
Change the active ingredient group if you have to spray again.

Spraying late after deep penetration into the body is much less effective.

Follow-up by stage

Branches

Deeply observed.
Check to see if the tree can produce compensatory branches.
Don't rush to spray if the population is low.

Making the field — flowering

Check the nest every 5-7 days.
Pay attention from the beginning of flowering to the end of flowering.
Handle when threshold is exceeded.

After flowering

Record the percentage of silver cotton.
Evaluate the effectiveness of this department to adjust the next one.

Monitor periodically

[ ] Number of eggs per square meter.
[ ] Bud mortality rate.
[ ] Ratio of silver cotton.
[ ] Rice stage.
[ ] Sowing schedule compared to region.
[ ] Amount of nitrogen fertilized.

This information helps distinguish whether fields are damaged by real stem borers or by other causes causing flat cotton.

Common mistakes

Wait until you see silver cotton before spraying: damage has been done.

Spraying at the seedling stage when population density is low: wastes crop-protection products and harms natural enemies.

Not checking the eggs: missing the moment when the new worms hatch.

Excess nitrogen fertilization: dense plants, easy to grow worms.

Sown late alone: the field becomes an attraction for butterflies and caterpillars.

Take notes

Date of nest discovery.
Number of eggs per square meter.
Date of spraying and active ingredients.
The rate of death of buds and silver flowers.
Yield at the end of the season.

After 2-3 crops, growers will know at what stage their fields usually need stem borer prevention.

References

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