Instructions for preventing rice-damaging mosquitoes

Onion mosquitoes cause damage from the seedling stage to the end of tillering, causing rice buds to turn into onion-like tubes and not flower. Instructions for identifying and cleaning secondary hosts, monitoring light traps and rooms by 3 down, 3 up, 1 right, 5 down.

Summary: Rice onion mosquitoes are often mistaken for abnormal budding or slow growth of rice. The larvae burrow into the growth tip, causing the young leaves to not open normally but to elongate into a tube like an onion stem. Damaged buds cannot flower. This article provides guidance on early identification and prevention through field hygiene, secondary host management, light trapping and balanced farming.

Applies to: paddy fields from the seedling stage to the end of tillering, especially in areas with wild rice, wild rice and host grasses around the field.
Duration: Monitor from before sowing to the end of tillering.
Difficulty level: Medium. It is necessary to detect through the "onion stem" buds, not wait until mass loss of buds occurs.
Estimated additional costs: Mainly field cleaning; Chemical treatment should only be considered when density is high and according to local recommendations.

How harmful are onion mosquitoes

Onion mosquitoes appear and cause damage all year round, but are most dangerous from the seedling stage to the end of tillering.

Harmful process:

Adults lay eggs near the base of leaf blades or leaf sheaths.
The larvae hatch and then enter the growing tip.
The larvae secrete substances that clog young leaves.
The leaves still grow longer but roll into tubes, looking like onion stems.
Damaged buds gradually dry out and do not bloom.

A bud that has become an "onion" is no longer able to produce flowers. Therefore, early prevention is more important than late treatment.

Identification signs

Most characteristic sign:

Rice shoots grow into round tubes, light green, like onion stems.
This tube does not spread leaves normally.
There may be larvae inside.
The damaged bud then dries and dies.
The field is severely damaged and shows sparse buds and poor tillering.

Unlike leaf rollers, onion mosquitoes do not roll the outer leaves and then eat the parenchyma. It directly destroys the growth peak.

Favorable conditions

Onion mosquitoes thrive when:

Temperature is about 26-30 degrees Celsius.
High humidity 85-95 percent.
There is fog, the sky is gloomy.
The field has a lot of rice and wild rice.
Field banks and canals have host grasses such as northern grass, pipe grass, abyssal grass, and western hair grass.
Unbalanced fertilization, especially high nitrogen.

If rice mites and weeds are not treated after harvest, onion mosquitoes will have a place to survive until the next crop.

Room before the case

Plowing and drying the land

Plow immediately after harvest.
Let the soil dry for at least 15 days if conditions allow.
Bury or destroy rice flakes.
Clean the soil thoroughly before sowing.

Soil drying helps shorten pest life cycles and reduce secondary hosts.

Hygiene of secondary host

Before sowing, you need to clean up:

Rice in the field.
Wild rice in canals.
Avalanche grass, tube grass, grass around the shore.
Dense grass close to the edge of the field.

Sanitation only in the fields is not enough. Mosquitoes can survive on banks and ditches and then fly into young paddy fields.

Sow concentratedly and simultaneously

If the sowing schedule is off schedule, there will always be young rice for harmful mosquitoes. Simultaneous sowing in the area helps cut off food sources continuously.

Management in the case

Follow the light trap

Light traps help detect the peak of adult mosquitoes:

Monitor the number of insects entering the trap.
When the number increases, check the seedling and tillering fields more carefully.
Incorporate local notices if any.

The light trap is not to decide to spray immediately, but to know when to visit the field more closely.

Balanced farming

Apply 3 down, 3 up, 1 right, 5 down.
Do not sow too thickly.
Do not fertilize with excess nitrogen.
Increase phosphorus and potassium according to plant needs.
Fertilizers containing calcium, magnesium, and silicon can be added to keep plants strong and healthy.

Healthy rice and well-ventilated fields are less likely to be severely damaged.

Limit medication early

Do not spray chemical crop-protection products for 0-40 days after sowing if not absolutely necessary. During this period, it is necessary to keep natural enemies and avoid ecological imbalance in the fields.

When discovering onion stalks

If there are only a few odd buds:

Mark area.
Check 5 points in the field.
Count the percentage of damaged buds.
Clean the banks and grass around the field immediately.
Follow up for another 3-5 days.

If the rate of damaged buds increases rapidly:

Contact local agricultural extension or plant protection to determine appropriate population and crop-protection products.
Do not mix many medications yourself.
Do not use growth stimulants from the seedling to tillering stage because it can make the field green and soft, making it more susceptible to pests and diseases.

Monitor periodically

[ ] Number of "onion" shoots per square meter.
[ ] Rice stage: seedling, early tillering, late tillering.
[ ] Is there any wild rice around the field?
[ ] Number of adult mosquitoes recorded in light traps.
[ ] Amount of nitrogen fertilized.
[ ] Condition of grass on field edges and canals.

Recording by week helps know whether onion mosquitoes appear early or late compared to the sowing schedule.

Common mistakes

Do not clean the rice plants: keep the mosquito source for the next crop.

Mistaking onion stalks for regular rolled leaves: mishandling the wrong object.

Massive early spraying: harms natural enemies, not necessarily effective against larvae in buds.

High nitrogen fertilization helps rice to compensate for tillering: green plants become soft, other pests and diseases easily increase.

Off schedule sowing in the area: creates a continuous source of young rice for onion mosquitoes.

Take notes

Sowing date.
The date the first onion shoots were discovered.
Proportion of damaged buds.
Condition of rice flakes/grass around the field.
Number of mosquitoes entering the light trap, if any.
Measures processed and results after 7 days.

If a field is repeated many times, it is necessary to review post-harvest and secondary host hygiene.

References

*Instructions for preventing rice-damaging mosquitoes* — Hainong technical document.
*Integrated pest management for rice* — Plant Protection Department.
*Rice IPM Handbook* — FAO Vietnam.