Instructions for preventing brown planthoppers from damaging rice

The brown planthopper both sucks the sap and burns the plant and transmits the yellow dwarf-dwarf leaf curl virus. Spray threshold, rotating active ingredients and brown plant hopper IPM combined with rice blast for the winter-spring crop in the Mekong Delta.

Summary: Brown planthopper (*Nilaparvata lugens*) is the number 1 most dangerous rice pest in the Mekong Delta. Unlike leaf rollers or thrips, brown planthoppers have two harmful effects: sucking sap and "burning" the planthopper + transmitting the yellow dwarf virus. If the orchard has a virus, crop-protection products cannot save it. This article focuses on the standard IPM spray threshold + how to rotate active ingredients to avoid drug resistance.

Applies to: OM, IR, ST, Dai Thom rice in the winter-spring crop of the Mekong Delta. Part of the Red River Delta (white-backed planthoppers are more common).

Duration: Monitor from 15 days after sowing to flowering. The most important stage is the tillering + growing stage.

Difficulty level: Medium. Need to count leafhoppers correctly + choose the right time.

Estimated additional costs: Spraying at the correct threshold is 250-450 thousand/acre/crop. Incorrect spraying = 2-3 times wasted + drug resistance.

Harmful effects + reasons why brown planthoppers are dangerous

Brown planthoppers are sap-sucking insects. 2 harmful effects:

Sucking tree sap:

• Yellow trees, "hopper burn" — dry spots starting in the middle of the field, spreading out.
• High density of 200-500 birds/m² → widespread fire in 7-10 days.

Virus transmission:

• Yellow dwarf virus (RYSV) + leaf curled dwarf virus (RGSV) is transmitted through brown planthopper saliva when sucking.
• Virus infected plants = short, have few branches, no or flat flowering. There is no cure for the virus.
• orchard has 5% dwarf yellow plants = spread in 3-4 weeks.

→ This is why controlling brown planthoppers must be prevention, not treatment. Waiting for the dwarf yellow tree to spray for leafhoppers is too late.

Leafhopper life cycle + reason for outbreak

There are 3 types of brown planthoppers:

• Eggs: laid in leaf sheaths. 5-7 days to hatch.
• Young planthoppers: 5 years old, eat continuously, at the beginning of this period they are most likely to die when sprayed.
• Adult leafhopper: winged + wingless. Long wings spread out in the fields, short wings stay and lay many eggs.

A female lays 100-300 eggs. In 25-30 days, a pair of leafhoppers can produce thousands of insects.

Outbreak occurs when:

• Thick sowing + high nitrogen fertilization — leaves are soft, abundant, hoppers eat well.
• Weather is humid + warm 25-30°C — winter-spring crop in the Mekong Delta.
• No natural enemies (due to indiscriminate spraying to kill natural enemies such as ladybugs and wolf spiders).

IPM standard spray threshold (no mist spraying)

This is the most important part. Many growers spray "rooms" periodically creating:

• Cost of money + effort.
• Destroy natural enemies → the next crop of leafhoppers will have a stronger outbreak (called "resurgence").
• Aphids are resistant to drugs.

Spraying threshold according to IPM (FAO + Plant Protection Department):

Counting method: mark the rice sheaths in 10 random clusters at 5 points in the field. Count the number of leafhoppers on each clump. Take the average.

Below threshold → DO NOT spray. Counting on next week.

Over the threshold → spray immediately, correct active ingredients + correct technique.

Room — four layers of protection

Choose resistant varieties

Priority is given to varieties with average — good resistance genes to brown planthoppers: OM5451, OM6976, OM7347, ST24, ST25. Updated list by season at the local Department of Agriculture.

Sparse sowing + balanced nitrogen fertilization

• Sowing 80-120 kg/ha (instead of 150-180 kg as usual).
• Reduce protein by 15-20%. High protein = dark green leaves = hoppers like it.
• Increase potassium in the tillering + flowering stage.

Protect natural enemies

Natural enemies of brown planthoppers in fields:

• Ladybugs, wolf spiders, parasitic wasps — eat leafhoppers every day.
• 5-year-old penguin (Cyrtorhinus) — sucks hopper eggs.

How to protect:

• DO NOT spray extensively unnecessarily.
• When spraying, prioritize active ingredients that are less harmful to natural enemies (Buprofezin, Pymetrozine).
• Plant trees on the edge of the field with small flowers (holy basil, lemongrass) as a habitat for natural enemies.

Monitor regional epidemic warnings

The Mekong Delta has an epidemic warning system of the Department of Plant Protection. When the province issues a warning about brown planthopper migration (moving from area A to area B), priority is given to field inspection + preventive spraying if necessary.

Spray correctly — choose active ingredients + technique

Active ingredients by mechanism group (rotate to avoid resistance)

Group 1 — early season priority:

• Buprofezin (Applaud, Butyl) — inhibits molting, effective for 2-3 year old leafhoppers.
• Pymetrozine — anti-injection.

Group 2 — when density is high:

• Imidacloprid — neonicotinoid, fast-acting but easily resistant.
• Thiamethoxam + Buprofezin combined.

Group 3 — late season + drug resistance:

• Pyridaben + Imidacloprid combination.
• Etofenprox.

Rotation rule: DO NOT use the same group twice in a row. Maximum 2-3 sprays per crop, each time changing active ingredient group.

Spraying technique

• Spray in the cool afternoon from 4-6 p.m. or early in the morning when the dew has just dried.
• Spray low, near the base — leafhoppers are near the base, not on the top.
• The sprayer pressure is enough to cover the leaf sheaths. Spraying from high to high = ineffective.
• After 24 hours of spraying, drain the field temporarily if the density of planthoppers is high (hoppers do not like dryness).

When you have a dwarf yellow tree

This is bad news. Steps to take immediately:

1. Pick up all diseased plants and take them away from the field — do not throw them in the field.
2. Spray to control leafhoppers immediately to reduce vectors. Fast active ingredient (Imidacloprid + Buprofezin combined).
3. DO NOT replant old varieties in empty spaces — soil/water damage.
4. If > 10% of the area is damaged → the possibility of saving is low. Consider cutting losses + preparing for the next crop with more resistant varieties.

Follow weekly

• [ ] Count hoppers at 5 points in the field (10 clusters/site), calculate the average per cluster.
• [ ] See if there are any dwarf/low/twisted yellow plants?
• [ ] Check natural enemies (ladybugs, spiders) — numbers compared to last week.
• [ ] Record the weather: temperature, humidity, wind direction (migrating leafhoppers often follow the wind).
• [ ] Compare neighboring fields: who explodes first, which direction is towards you?

Common mistakes

Spray hoppers according to schedule (spray once every 15 days even if hoppers are not seen yet): create resistance + kill natural enemies.

Spray on rice tops: hoppers near the base. Top spraying = water flows to the ground, ineffective.

Fertilize nitrogen when there are aphids: more nitrogen = more food for aphids = faster outbreak.

News "specific treatment to treat brown planthoppers" with unknown active ingredients: many different packaging products with the same active ingredient. Read the active ingredient label, not the trade name.

Ignore the province's epidemic warning: The Department of Plant Protection has data on hopper migration with the wind. The province issues a warning = there is a reason.

Take notes

• Sowing date + seed + amount of seed.
• Number of spraying sessions + active ingredients + days.
• Number of leafhoppers counted each week.
• Number of dwarf yellow trees, if any.
• Yield at the end of the season + flat rate.

After 2-3 cases, you will know the brown planthopper pattern in your area + have the ability to predict more accurately than the province's general warning.

References

• *Integrated pest management for rice* — Plant Protection Department, 2022.
• *Prevention of brown planthoppers that damage rice* — Mekong Delta Rice Institute, 2023.
• *Rice IPM Handbook* — FAO Vietnam, 2021.

Related articles

• Instructions for rice blast prevention
• Instructions for preventing yellow dwarf disease — twisted leaf stunt (rice)
• Guidelines for IPM integrated pest management for rice
• Track today's rice price and 30-day forecast