Instructions for preventing small leafroll pests on rice

Small leaf rollers roll rice leaves into tubes. The larvae eat the parenchyma, leaving white streaks along the leaf. Instructions on identification, spraying threshold of 20 larvae/m2 and prevention by sparse sowing, balanced nitrogen fertilization, and protection of natural enemies.

Summary: Small leaf rollers are familiar pests in paddy fields. Larvae roll leaves into tubes, located inside the green tissue, leaving white streaks that reduce photosynthesis. But you don't always have to spray when you see rolling leaves. Before 40 days after sowing, rice still has good recovery ability. This article guides you on how to count numbers and handle them correctly to avoid wasting treatment.

Applies to: Winter-spring, summer-autumn and autumn-winter rice in the Mekong Delta, Central and Northern regions.
Duration: Monitor from tillering to flowering, the most important stage is the tillering — flowering stage.
Difficulty level: Basic. You need to count the larvae, not just look at the rolled leaves.
Estimated additional costs: 200-500 thousand VND per pole if handled properly.

Identification signs

Small leaf rollers cause damage in a very specific way:

Rice leaves are rolled into tubes.
The larva is located inside the rolled leaf.
The worm scrapes the green parenchyma, leaving the white epidermis.
White streaks run along the leaf veins.
When you open the rolled leaves, you can see light green larvae.

Adult butterflies are pale yellow with brown stripes on their wings. Eggs are usually laid along leaves.

Impact on productivity

The amount of damage depends on the rice stage:

Before 40 days after sowing: rice can still produce new leaves, usually does not cause major damage if the population is low.
Stage of growing rice: damaging rice leaves and functional leaves, directly affecting cotton farming.
The flowering stage: if the leaves are severely damaged, the seeds are poorly placed, and the flat rate increases.

Therefore, the decision to spray must be based on insect population and rice stage.

Conditions for worms to thrive

Small leaf rollers often increase when:

The fields are sown thickly.
Excess nitrogen fertilization results in green rice with soft leaves.
Continuous intensive farming.
The weather is dry and humid.
Spraying too much crop-protection product causes loss of natural enemies.

Many fields are severely affected by leaf rollers, not because of lack of crop-protection products, but because of early spraying, killing ladybugs, spiders and parasitic wasps.

When to spray

Commonly used threshold:

Do not spray for the first 40 days if the population is low.
Stage of planting — flowering: treat when the population is above 20 larvae per square meter.
If worms concentrate in each cluster, spray locally according to the previous cluster.

How to count:

Choose 5 points in the field.
Each test point is 1 square meter.
Open the rolled leaves to count the live larvae.
Calculate the average for the entire field.

Just counting the leaves is not enough, because many leaves are empty or the worms have pupated.

Prevention by farming techniques

Sow sparsely, sow simultaneously

Sow according to local recommendations, avoid sowing too thickly.
Sow simultaneously in the area to cut off the worms.
Clean the soil and clean the field edges before sowing.

Moderately sparse fields help open the rice canopy, making it difficult for pests to break out.

Apply balanced fertilizer

Do not fertilize with excess nitrogen.
Supplement potassium during tillering and flowering stages.
Do not "spray more urea to make it green" when there are worms.

Rice leaves that are too green and soft are good food for leaf rollers.

Protect natural enemies

Natural enemies of leaf rollers include:

Bees parasitize eggs and larvae.
Spider catching prey.
Ladybug.
The bugs eat their prey.

Do not spray broad-spectrum crop-protection products in the early stages if the threshold has not been exceeded. This is the best way to keep natural enemies.

Spray when the threshold is exceeded

Active ingredients commonly used according to labels and local recommendations:

Abamectin.
Emamectin benzoate.
Azadirachtin.
Chlorantraniliprole.

Spraying technique:

Spray when the worms are still young.
Spray in the cool afternoon.
Spray enough water to get the treatment into the rolling leaves.
Do not spray before rain.
Change the active ingredient group if you have to spray a second time.

The worms have grown large and the leaves have become white, so spraying will only reduce the next generation and cannot restore the leaf tissue that has been eaten.

Phased treatment

Before 40 days after sowing

Tracking is key.
Do not spray.
Keep fields healthy, fertilize properly.
Protect natural enemies.

Making fields

Check the functional leaves and bamboo leaves.
Count larvae per square meter.
Handle if threshold is exceeded.

Growing — sucking milk

Limit unnecessary spraying.
If the number is high, choose the drug with the correct label and pay attention to the quarantine period.
Spray locally if worms are not evenly distributed.

Monitor periodically

[ ] Number of rolled leaves per square meter.
[ ] Number of larvae still alive in rolled leaves.
[ ] Rice stage: 40 days before, planting, flowering.
[ ] Most recent nitrogen fertilization level.
[ ] Density of natural enemies in the field.

Recording both the number of worms and the stage of rice will help make more accurate spraying decisions.

Common mistakes

If you see leaves curling, spray immediately: many leaves have no worms, spraying is not necessary.

Preventive spraying 40 days after sowing: kills natural enemies, easily breaks out pests in the next generation.

High nitrogen fertilizer after seeing worms: makes young leaves softer, making worms eat more strongly.

Not opening leaves to count worms: confusing old damaged leaves with live worms.

Using an active ingredient continuously: increases the risk of drug resistance.

Take notes

Date of discovery of rolling leaves.
Number of larvae per square meter.
Rice stage.
Active ingredients sprayed, date of spraying.
Results after 5-7 days.
Yield at the end of the season.

After a few crops, growers will know when their fields are usually affected by leaf rollers so they can monitor sooner.

References

*Instructions for preventing small leafroll insect in rice* — Hainong technical document.
*Integrated pest management for rice* — Plant Protection Department.
*Rice IPM Handbook* — FAO Vietnam.