Instructions for preventing grain blemish disease on rice

Smudging causes rice grains to change color, shrink, become sterile or flat, reducing rice quality. Instructions for prevention from clean seeds, balanced fertilization, insect management during the flowering — ripening stage and timely spraying before/after flowering.

Summary: Smearing is not a single disease. It is the result of many factors: fungi, bacteria, sucking insects, spider mites, unbalanced nutrition and humid weather during the flowering period. This article provides instructions on how to prevent each stage, especially about 7 days before and after flowering, when seeds begin to form and are very susceptible to the disease.

Applies to: Winter-spring, summer-autumn, fall-winter rice crops; The field has rainy and humid weather at flowering time or has a history of loose seeds.
Duration: Room from seeding to flowering; The most important is 7 days before flowering and 7 days after flowering.
Difficulty level: Medium. Need to combine nutrition, pests and weather.
Estimated additional costs: 300-700 thousand VND per acre if cotton disease prevention must be sprayed.

What is grain lem

Smudging of seeds often appears on seeds during the ripening stage. Expression:

Husk has dark brown or black spots.
Seeds change color to red, yellow, orange, pink or black depending on the severity of the disease.
Rice grains become dark and lose quality.
Seeds are shriveled, sterile or flat.
Cotton has a lot of bad seeds, the seeds don't go in well.

The disease reduces both yield and selling price because of bad seeds and poor color rice.

Common causes

Small grain has many causes at the same time:

Fungi and bacteria cause diseases on cotton and seeds.
Continuous rain during the flowering period.
Cloudy weather, high humidity.
Excess nitrogen fertilization during the flowering stage.
The panicle spider damages leaf sheaths, panicles and seeds.
Aphids, stink bugs or sucking insects on cotton.
Sensitive varieties or seeds that are not disease-free.

For many reasons, one-way processing is often not enough. Must be in a general room.

Disease conditions thrive

Grain smearing pressure increases when:

The rice blooms and meets the rain.
The fog persisted early in the morning.
The fields are fertilized late with nitrogen, the rice canopy is densely green.
Water and nutrient levels fluctuate strongly.
The field has rice spiders, stink bugs, leafhoppers or cotton blast disease.

The flowering stage is an important gateway. If the weather is bad at the time of flowering, you need to monitor more closely than usual.

Prevention from breeding

Use disease-free seeds.
Do not take seeds from fields that are heavily soiled.
Remove flat and bad seeds before soaking.
Treat seeds according to local recommendations if seed disease is present in the area.

Clean varieties do not guarantee that the field will not be contaminated, but they reduce the initial source of disease.

Apply balanced fertilizer

Principle:

Do not over-fertilize with nitrogen during the budding-flowering stage.
Increase potassium at the right time to harden plants and firm seeds.
Use the rice leaf color chart to decide whether additional nitrogen fertilizer is needed or not.
Do not fertilize nitrogen when the field is sick or the weather is cloudy for a long time.

Late nitrogen makes the rice canopy green, moist and soft, creating conditions for cotton disease.

Managing insects and spiders

Before and during the flowering stage, it is necessary to check:

Spider spider: purple leaf sheaths, flat flowers.
Stink bugs: suck young seeds.
Brown planthopper: root density and virus risk.
Leaf roller: seriously damaged rice leaves, reducing cotton production.

Do not spray crop-protection products indiscriminately. Only handle when the threshold is exceeded, for the right object, at the right stage.

Spraying to prevent cotton diseases

Consider spraying just in case:

The field has a history of grain stains.
The weather forecast is rainy/humid at flowering time.
Dense green fields due to excess nitrogen.
There are spider mites or other diseases on the sheaths and flowers.

Usually used time:

7 days before blooming.
7 days after flowering.

Active ingredients refer to labels and local recommendations:

Kasugamycin.
Ningnanmycin.
Oxolinic acid.
Propiconazole.
Difenoconazole.
Active ingredients suitable for cotton diseases.

Do not mix too much treatment in one bottle. It is necessary to read the label regarding mixing capacity and isolation time.

Follow up after flowering

[ ] Rate of flower blooms.
[ ] Does cotton seeds change color prematurely?
[ ] Are there any spiders or stink bugs?
[ ] Will it rain/damp for a long time during flowering?
[ ] Proportion of flat seeds and badgers after suckling milk.
[ ] Spraying schedule before/after flowering.

Monitoring after flowering helps evaluate whether spraying is at the right time.

Common mistakes

Only spray when the grain is clearly smeared: by this time most of the damage has been done.

Late nitrogen fertilization to "raise cotton": easily causes disease and increased flatness.

Ignore spiders and stink bugs: insects create wounds and flatten seeds.

Mixing multiple chemicals in one spray session: increases the risk of leaf scorch, reduces effectiveness.

Don't pay attention to the quarantine period: you have to be very careful near harvest.

Take notes

The day the rice blooms.
Weather 7 days before and after flowering.
Active ingredients sprayed, date of spraying.
Condition of spiders, stink bugs, and leafhoppers.
Ratio of smudged/flaky seeds at harvest.
Rice yield and quality.

After a few crops, growers will know which fields need to be sprayed to prevent cotton diseases, and which fields only need to be monitored.

References

*Instructions for preventing grain blemish disease in rice* — Hainong technical document.
*Integrated pest management for rice* — Plant Protection Department.
*Rice IPM Handbook* — FAO Vietnam.