Spraying process for rice in the flowering — ripening stage

The flowering — ripening stage is when you need to protect the flowers, seeds and leaves, but you must pay close attention to the isolation time. Guidance on deciding to spray cotton collar blast, grain smut, panicle spiders, stink bugs and leafhoppers according to IPM.

Summary: From flowering to ripening, the rice plant has entered the stage that determines grain quality. Correct spraying can reduce cotton collar blast, grain smearing, panicle spiders, stink bugs and leafhoppers; Spraying incorrectly can increase residue, burn leaves or waste quarantine time. This article guides the process of checking and deciding to spray according to field conditions, not spraying out of habit.

Applies to: Rice in the stage of preparation for flowering, flowering evenly, hydrated with milk, firm and green until ripe.
Duration: About 25-35 days at the end of the season depending on the variety.
Difficulty level: Medium. It is necessary to determine the correct flowering stage and pay attention to the isolation time.
Estimated additional costs: 300-800 thousand VND per acre if you have to spray to prevent cotton diseases or treat pests at the end of the season.

Target stage of flowering — ripening

At this stage, protection is needed:

Pong leaves.
Cotton collar.
The flowers are blooming.
The seeds are holding milk and are firm.

Injury at this stage directly affects rice yield and quality. But this is also the period near harvest, so every spraying time must consider the isolation time.

Objects to monitor

Cotton-neck rice blast

The cotton neck is dark, the cotton is dry, and the seeds are flat.
There is a high risk when there has been leaf blast and the weather is humid and dew.
The best prevention is 5-7 days before flowering if the field is at risk.

Small grain

Seeds change color, brown/black, loose.
Increases strongly when it rains, high humidity when flowering.
Need to prevent about 7 days before and after flowering if the field is at risk.

Spider mites and stink bugs

The spider mite makes the sheaths purple and flat.
Stink bugs suck on young seeds, causing flat seeds and bad rice.
It is necessary to directly check the cotton and leaf sheaths.

Brown planthopper at the end of the season

The hoppers accumulate from the beginning of the season, easily causing a hopper fire at the end of the season.
Spraying must pay attention to isolation time and location at the root.

Checklist before spraying

[ ] The rice is just before flowering, does it flower evenly or is it full of milk?
[ ] The main target is cotton disease, spider mites, stink bugs or leafhoppers?
[ ] Has the disease density/prevalence exceeded the threshold?
[ ] Is there any forecast of rain, dew, or high humidity in the next 3-5 days?
[ ] How long is the drug expected to be quarantined?
[ ] Do I need to spray the entire field or just spray clusters?

Close to harvest, one wrong spray can cause a loss of safety standards.

Spraying to prevent cotton diseases

Consider spraying when:

The field has a history of rice blast or grain stains.
Weather is humid, lots of dew, rain at flowering time.
The rice is green and dense due to excess nitrogen.
There are spider mites or other pests causing wounds.

Usually used time:

5-7 days before flowering for rice blast.
About 7 days before and after flowering to allow the seeds to spread if the risk is high.

Choose medications according to labels and local recommendations. Do not mix too much active ingredient in one spray.

Treating insects at the end of the season

Stink bugs

Check early morning or late afternoon.
Concentrated in fields with uneven flowering, near grass edges.
Only treat when the population is high and causes damage to young seeds.

Spiders

Check the leaf sheaths for purple stains.
If the rate of symptomatic sheaths is 5-10 percent, consider treatment.
Before spraying water into the field at the right level for spiders to move up.

Brown planthopper

Counting at the rice base.
Spray low, do not spray on cotton.
Choose a drug with an appropriate quarantine period.
Do not spray if you are about to harvest but the population does not pose a risk of leafhopper fire.

Spraying technique during flowering — ripening stage

Spray in the cool afternoon.
Avoid when rice is drying in full color if the drug has the risk of affecting pollination.
Do not spray before rain.
Use enough water to evenly cover the leaves and cotton if spraying for cotton disease.
Spray low at the base if treating leafhoppers.
Read the quarantine period carefully.

A common mistake is using the same spray method for every object. Cotton disease requires covering the cotton/field leaves, while brown planthoppers stay at the base.

When not to spray

Rice is about to be harvested and treatment does not guarantee quarantine.
Diseases/pests are below the threshold, the field is recovering well.
It's about to rain heavily.
The tree is suffering from heat shock and severe water shortage.
The harmful object cannot be identified.

Not spraying is sometimes the best decision, especially at the end of the season.

Post-injection monitoring

[ ] Will the disease stop spreading after 5-7 days?
[ ] Will the cotton bloom?
[ ] Is the ratio of flat/half-sized seeds increasing?
[ ] Are there still high populations of leafhoppers/bugs/spiders?
[ ] Does the expected harvest date still warrant quarantine?

After spraying, do not automatically spray again if the field is fine.

Common mistakes

Spraying too close to harvest date: easy to violate quarantine period.

Spraying hopper crop-protection product on cotton: hoppers are at the base, low efficiency.

Spraying for cotton diseases after the seeds are heavily stained: damage has already occurred.

Mixing multiple chemicals to "make sure": increases the risk of leaf burn, reduces safety.

Don't check the weather at flowering time: rain and dew determine the risk of cotton disease.

Take notes

The day blooms smoothly, blooms evenly, and sucks milk.
Spray target.
Active ingredients, dose, isolation time.
Weather during spraying.
Estimated harvest date.
Ratio of loose/firm seeds at harvest.

Write clearly to help you know whether the field really needs to be sprayed to prevent cotton disease in the next crop.

References

*Spraying process for rice in the flowering — ripening stage* — Hainong technical document.
*IPM Integrated Pest Management Guide* — Hainong technical document.
*Rice IPM Handbook* — FAO Vietnam.