Apart from fungal and physiological diseases, rubber plantations in Vietnam often suffer from environmental, climatic, and chemical stresses such as sun scorch, lightning strikes, cold injury, storm damage, and chemical toxicity.
These factors cause significant economic losses and reduce the productivity and lifespan of rubber trees if not managed properly.
1. Sun Scorch (Cháy nắng)
Table of Contents
Causal Factors
Caused by excessive heat and solar radiation, particularly when:
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Young trees are transferred suddenly from shade to full sunlight.
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Soil moisture is low and daily temperature variation is high.
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Improper mulching or basin construction increases heat reflection from lateritic soil.
Distribution
Occurs mainly during the dry season in nurseries, young plantations, and pre-tapping trees (KTCB).
Symptoms
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Leaves show patchy burns, turning silvery-white to brown, then wilt and drop.
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Young shoots wither and die due to dehydration.
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On young trunks (0–20 cm above ground), lance-shaped sunken lesions appear, bark dies, and the damage usually faces west or southwest.
(See Figure IX.13)
Treatment
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Maintain sufficient irrigation during cool hours in nurseries.
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For young trees: construct basins and mulch carefully, keeping mulch 10 cm from the trunk.
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Whitewash trunks with 5% lime solution in areas prone to sun scorch.
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If shoots die: cut diagonally 10–20 cm below the dead tissue and apply vaseline to seal the wound.
2. Lightning Strike Damage (Sét đánh)
Causal Factor
Caused by high-voltage electrical discharge during thunderstorms.
Distribution
Occurs randomly during rainy seasons, especially at the transition between dry and wet periods.
Symptoms
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Damage is instantaneous: foliage wilts rapidly as if scalded by boiling water.
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Leaves fall while still green, bark becomes dry and dark brown.
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The latex coagulates, leaving white fibrous streaks under the bark.
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Wood beneath the cambium turns black-streaked, and within 1–2 weeks, borer dust (yellowish powder) appears.
(See Figure IX.14)
Treatment
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Detect early; cut 20–30 cm below the affected section and apply vaseline.
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Whitewash damaged trunks with 5% lime solution.
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Suspend tapping on affected trees until full recovery.
3. Cold Injury (Rét hại)
Causal Factor
Prolonged exposure to temperatures below 10°C.
Distribution
Common in northern highlands or valleys, especially north-facing slopes during winter.
Symptoms
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Young leaves deform and die, mature leaves dry up.
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The apical bud turns black and necrotic, extending down the stem.
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Cracks appear on the trunk with yellow sap oozing, later turning into latex streaks.
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Prolonged frost may kill entire trees.
(See Figure IX.15)
Treatment
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Avoid growth stimulants or foliar fertilizers during cold periods.
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Apply mulch around roots to improve cold tolerance.
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On young trees: cut below dead tissue (10–20 cm) and seal with vaseline.
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Remove necrotic bark and apply vaseline on exposed wood.
4. Wind, Storm, or Mechanical Damage (Thiệt hại do gãy đổ)
Management Steps
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After storms or typhoons, promptly:
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Assess and record damage, classify by severity (leaning, uprooted, broken trunk, snapped branches).
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Report to the corporation for recovery planning.
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Treatment Based on Tree Condition
| Condition | Recommended Action |
|---|---|
| Young plantations (KTCB) | Firm soil around the roots to stabilize the tree. |
| Broken or split stems | Cut diagonally 20 cm below the wound and apply vaseline. |
| Bent or leaning trees | Prune affected branches to balance canopy; support or straighten if possible. |
| Heavily damaged or uprooted trees | Remove and replant (salvage logging if necessary). |
Safety and Recovery Notes
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Ensure worker safety during clearing.
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Remove debris promptly to prevent fire hazards.
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Mark and record trees designated for removal to avoid confusion during felling.
5. Chemical or Fertilizer Toxicity (Ngộ độc thuốc BVTV, phân bón)
Causal Factor
Overexposure to pesticides or fertilizers at concentrations exceeding safe limits.
Symptoms
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Mild cases: leaf distortion, wrinkling, wavy edges.
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Severe cases: burned spots (necrosis), yellowing, leaf curling, defoliation, shoot dieback, and emergence of abnormal basal shoots.
(See Figure IX.16)
Treatment
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For pesticide or foliar fertilizer burn:
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Rinse foliage thoroughly with clean water.
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For fertilizer toxicity:
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Flush the soil heavily with water to leach out excess salts.
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If shoots die: cut diagonally 10–20 cm below the damaged area and apply vaseline to the wound.
Conclusion
Non-pathogenic stresses like sun scorch, lightning, frost, and chemical toxicity often cause as much damage as fungal diseases in rubber plantations.
Proactive prevention — through proper care, balanced fertilization, and early intervention — remains the best way to protect tree health and maintain latex yield.