Experts share ways to overcome pests and diseases that damage winter-spring rice that cannot be ignored

In the winter-spring crop, brown planthoppers, leaf rollers, rice blasts, premature yellowing of leaves, grain smearing, and powdery mildew are often encountered in the winter-spring crop. Instructions on how to visit fields, recognize early and properly handle thresholds to reduce costs and maintain productivity.

Summary: The winter-spring crop in the Mekong Delta has high productivity but is also a crop that is prone to outbreaks of many pests and diseases at the same time. From the flowering stage to harvest, growers often encounter rice blast, premature yellowing of leaves, grain smearing, brown planthoppers, leaf rollers and whiteflies. This article brings together the main subjects in an easy way to visit the field: look at symptoms, know treatment thresholds, and avoid spraying based on emotion.

Applies to: Winter-spring rice in the Mekong Delta, especially at the stage of flowering — flowering — milking — ripening.
Duration: Monitor every 5-7 days; Increase to every 2-3 days when the weather is cold at night, sunny at noon, and dew is heavy.
Difficulty level: Medium. It is necessary to examine the copper in the correct position and read the symptoms.
Estimated additional costs: 300-800 thousand VND per acres per crop if handled properly; Spraying on the wrong schedule can cost twice as much.

Why is the winter-spring crop prone to pest outbreaks

From December to March, the weather usually has:

Cold night, sunny noon.
There is dew in the early morning and evening.
High humidity in the rice canopy.
Unseasonal rain or localized drizzle.
Green rice is good due to strong nitrogen fertilization at the beginning of the season.

This condition is favorable for rice blast, grain smearing, premature yellowing of leaves and brown planthoppers. If you sow thickly, fertilize with too much nitrogen, and spray crop-protection products early, you will lose natural enemies, and pest pressure will increase.

Principle of field visit

Don't visit the fields like standing on the shore and looking at the color of the fields. Need to go into the field:

Select 5 points in an X shape.
Each point observes 10 clusters.
Check the root, middle leaves, upper leaves and flowers.
Write down the location of the disease or pest.
Compare with the next field to know if the disease is spreading or just localized.

Many diseases start where the rice is green, dense, and has excess nitrogen. This is a must-see location.

Rice blast disease

Sign

Rhombic-shaped lesions on leaves.
Dark brown or dark green border.
The middle of the lesion is gray and white.
When the weather is foggy, the disease spreads very quickly.

Cotton rice blast is more dangerous than leaf blast. When the cotton neck is black, dry, and the seeds are flat, it is almost too late.

How to handle

When you see typical lesions, stop fertilizing with nitrogen.
Spray specific blast treatment chemicals according to the label, prioritizing active ingredients such as Tricyclazole or locally recommended active ingredients.
Spray for prevention before flowering and about 7 days after flowering if the field is at high risk.
Do not spray early in the morning while there is still dew or before rain.

Early ripening yellowing disease

Sign

The disease often appears after flowering, when the rice is in milk:

The leaves near the base have orange-yellow round dots.
The yellow streak extends from the base of the leaf to the tip of the leaf.
The fields look golden in the morning in clusters.
If it's heavy, the leaves will dry quickly and the seeds will be poor.

How to handle

Check carefully the lower layer of leaves, especially where the rice is thick.
Use specific medications according to local recommendations, often with active ingredient groups such as Azoxystrobin, Mancozeb, Metalaxyl or appropriate combinations according to the label.
Fertilize with balance, avoid late nitrogen.
Keep the water stable, don't let the field dry out and crack during the milking period.

Yellow leaves due to weather

Not all yellow leaves are a disease. The winter-spring crop may experience physiological yellowing due to cold:

The tips of the leaves are slightly burned and dry.
Yellow leaves but no obvious disease spots.
Appears after a prolonged period of cold or dew.
Fields may yellow more evenly, not following clear disease spots.

How to handle:

Keep water moderately submerged to reduce cold shock.
Supplement potassium when cold is forecast.
Spray foliar fertilizer with potassium, humate or trace elements if the plant is in decline.
Don't rush to spray crop-protection products until you see clear symptoms of the disease.

Grain smudge disease

Small grain has many causes:

Fungi, bacteria on cotton.
Spider web.
Unbalanced fertilization.
Wet weather at flowering time.
The field is affected by rice blast or leaf cover burn.

The best way is to keep the plant healthy before it blooms:

Fertilize with balance, no excess nitrogen.
Stable water management.
Spray to prevent cotton diseases before and after flowering when the weather is unfavorable.
Can be combined with cotton blast prevention treatment if the label is correct and at the right time.

Brown planthopper

Brown planthoppers need to be checked at the base of the rice, not at the top.

When to process

When leafhoppers bloom.
Young leafhoppers are 2-3 years old, light yellow.
Density above 3 shrimp per shrimp in sensitive stage.
There is a risk of transmitting yellow dwarfism and leaf curling dwarfism.

How to handle

Spray low at the rice base.
Priority is given to anti-molting drugs or new generation special drugs to treat leafhoppers according to the label.
Do not add chrysanthemum root treatment to "strengthen it" because it can easily cause hoppers to flare up again and harm natural enemies.
Do not use active ingredients that are not suitable for the flowering stage if the label advises avoidance.

Leaf roller

Leaf rollers don't just spray leaves when they see them rolling.

Before 40 days after sowing, rice has good recovery ability.
Only treat when the population is high, about 20 larvae per square meter.
Prioritize spraying in clusters if pests are concentrated.
Protect natural enemies by not spraying early.

Fields sown thickly, fertilized with lots of nitrogen and sprayed with crop-protection products early are often more susceptible to leaf-rolling pests.

Whiteflies

Sign:

The white larvae are as small as pollen grains.
The larvae stick to the underside of leaves like sesame seeds.
Both larvae and adults are often found on the underside of leaves.
Insects fly slowly, prefer dense and windless places.

Because the body has a layer of powder/wax, when spraying you need to:

Spray the underside of the leaves thoroughly.
Use adhesives or additives according to label if necessary.
Choose the appropriate drainage medication.
Only treat when density is high, do not spray habitually.

Pest reduction technology

Apply 1 for 5 off.
Sow sparsely and simultaneously.
Balanced fertilization, reducing excess nitrogen.
Stay properly hydrated.
Do not spray crop-protection products in the first 40 days if the threshold has not been exceeded.
Monitor local pest forecasts.

A healthy field floor helps reduce the number of spraying times more than any "strong treatment".

Monitor periodically

[ ] Blast: diamond-shaped marks on leaves and flower necks.
[ ] Yellow early ripe leaves: orange-yellow dots, yellow streaks from the base of the leaves.
[ ] Brown planthopper: density at the base, age of planthopper.
[ ] Leaf rollers: number of larvae per square meter.
[ ] Whitefly: underside of leaves, density on rice stalks.
[ ] Small grain: weather at flowering, disease on cotton.

Common mistakes

Spraying on a fixed schedule: costs money and causes loss of natural enemies.

Add nitrogen when you see yellow rice: if yellowing is caused by disease or leafhoppers, nitrogen will make the situation worse.

Just look at the color of the field from afar: many diseases start in the lower layer or at the base.

Spraying hoppers on rice tops: hoppers at the base, high spraying with low efficiency.

Spray for leaf rolling pests 40 days in advance even if the population is low: destroys natural enemies and increases the risk of pest outbreaks later.

Take notes

Sowing date, seed, amount of seed.
Fertilization schedule.
Pests and diseases are discovered day by day.
Active ingredients sprayed and time of spraying.
Results after 5-7 days.
Yield and flat rate at the end of the season.

After a few seasons, this data helps growers know which people in their fields usually get outbreaks and at what times.

References

*Experts share how to overcome pests and diseases of winter-spring rice* — Hainong technical document.
*Integrated pest management for rice* — Plant Protection Department.
*Rice IPM Handbook* — FAO Vietnam.