Pest control for oranges

The leafminer (Phyllocnistis citrella) carves zigzag lines in young leaves, weakening the plant and creating wounds for greening disease to spread. Instructions for prevention according to fortune + biological measures for orange orchards in Ha Giang and the Mekong Delta.

Summary: Leafminer does not kill orange trees immediately but weakens them in the long term — especially young trees. More dangerously, the wound left by the worm is the door for greening bacteria to spread. This article guides the prevention according to each bud break, focusing on biological measures and spraying at the right time — not spraying according to schedule.

Applies to: Ha Giang gourmet oranges, V2 oranges, Mekong Delta diamond oranges, Cao Phong oranges. Especially 1-5 year old nursery orchards.

Duration: Monitor all year round, focusing on young buds.

Difficulty level: Medium.

Estimated additional costs: 2-3 million VND per hectare per year.

Characteristics of the spell-painting worm

*Phyllocnistis citrella* is the larvae of a small moth. Features:

• Butterflies are very small — only 2-3 millimeters. Hard to see in the orchard.
• Lay eggs on young leaves — especially developing leaves, undersides of leaves.
• The larva burrows between the two layers of leaf epidermis — creating white, zigzag lines.
• Life cycle 18-25 days — many generations per year.
• Only attacks young leaves — old leaves have a hard cuticle that cannot be penetrated by worms.

Harmful effects:

• Young leaves are cloudy — not fully photosynthesizing.
• Long-term weak young trees — especially 1-3 year old trees lose many buds in a row.
• Wound = door to greening — the most dangerous disease of citrus.
• Decreased fruit quality — weak trees produce small fruit.

Life cycle of orange and leafminer

Orange has 3-4 periods of good fortune during the year:

• Spring Loc (February-March): weak, little depth.
• Summer fortune (May-July): many, deep and strong.
• Lucky autumn (September-October): average.

Each bud phase lasts 25-40 days from budding to full maturity. Leafminers only attack during the young leaf stage — when the leaves are old (dark green, hard), the worms no longer destroy them.

Prevention strategy: spray on the right season, don't spray outside of the season.

Recognize

On leaves

• White zigzag lines on the top or bottom of leaves.
• The line is 2-10 centimeters long, extending along the veins of the leaf.
• At the end of the line are worms — small worms 2-3 millimeters long, light yellow.
• Leaves become bent and lose their natural shape.

Count to evaluate

Count the young leaves with markings in 30 young leaves per tree × 5 trees:

Room according to fortune

Discovering new fortune

• Observe the tip of the branch — the buds are starting to swell.
• Young leaves are just starting to open — lighter green than older leaves.
• When 30-40 percent of the trees in the orchard bear fruit at the same time — start a prevention campaign.

Spraying for prevention at the beginning of the lucky season

When young leaves open 1-2 leaves:

• Spray *Spinosad* (biological treatment) or *Spinetoram* — less harmful to natural enemies.
• Or *Abamectin* — highly effective against larvae.

Spray in the cool afternoon, evenly on the underside of young leaves (where worms lay eggs).

Additional spraying in batch

If the worms still appear after 10-14 days:

• Spray a second time with another active ingredient.
• *Imidacloprid* (neonicotinoid) — penetrates plants, kills feeding insects.

After the leaves are completely old

• Stop spraying — pests do not attack old leaves.
• Watch for the next lucky draw.

Biological measures

Protect natural enemies

Natural enemies of leafminers:

• Parasite wasp species *Citrostichus phyllocnistoides* — lays eggs in larvae.
• Spider near leaves — eats larvae on leaves.
• Ladybugs eat leafminer eggs.

Protect natural enemies:

• Avoid spraying broad-spectrum crop-protection products (such as *Cypermethrin*) in orange groves.
• Plant trees on the edge of the orchard with small flowers.
• Limit spraying during the growing season.

Trap with yellow sticky paper

• Place 10-20 traps per hectare, hang 1.5-2 meters high.
• Yellow sticky paper attracts butterflies and talismans.
• Monitor the number of butterflies caught — predict the density in the orchard.

Management of young trees (1-3 years old)

Young trees are especially sensitive to leafminers:

• Young trees have many consecutive blooms — each phase is a window for worms.
• The leafminer prevents the tree from developing its canopy properly.
• The wound is susceptible to greening — a disease that cannot be cured on young trees.

Caring for young trees:

• Spray the room evenly each time.
• Watch mature trees more closely.
• Cut and burn heavily infected leaves — destroy nests of larvae.

Coordinate with the greening department

Because leafminers create the door for greening (greening disease caused by the bacteria *Candidatus Liberibacter asiaticus* transmitted by citrus psyllids), preventing leafminers = reducing the risk of greening:

• Burn trees with greening symptoms as soon as discovered — do not try to save them.
• Spraying to prevent psyllids and spraying for leafminers — both effective.
• Buy varieties with clean greening certification — avoid floating varieties.

Keep track of each fortune

• [ ] Starting date of the new lucky draw.
• [ ] Proportion of leaves with markings after 10, 20, 30 days.
• [ ] Number of butterflies in sticky paper trap.
• [ ] Natural enemies observed.
• [ ] Number of plants with greening symptoms.

Common mistakes

Spraying according to a fixed schedule: wasteful when there are no worms, not timely when worms break out.

Spray outside the bloom season: worms are not present on old leaves — spraying has no effect.

Use broad-spectrum drugs: kill natural enemies, long-term orchard loss of control.

Ignore plants with greening symptoms: spread to other plants via psyllids.

Spray only the top of the leaves: leafminers lay eggs on the underside. Both sides must be sprayed.

Take notes

• Calendar of lucky events of the year.
• Proportion of infected leaves per batch.
• Active ingredient sprayed + date.
• Number of trees detected with greening every year.

References

• *Prevention of leafminer pests on citrus* — Plant Protection Department, 2022.
• *Integrated pest management on citrus* — Southern Fruit Institute, 2023.
• *Prevention of greening disease on oranges* — Plant Protection Institute, 2023.

Related articles

• IPM integrated pest management in orange orchards
• Prevention of citrus ulcer disease and scar disease
• Techniques for pruning branches and creating canopy for orange trees
• Calculate fertilization recommendations