Cause
- El Nino dry spells in Malaysia (2015-16, 2019, 2023) with rainfall below 100 mm/month for 3+ months.
- Sandy or shallow soils with poor water-holding capacity.
- Slope aspect on hilly blocks (west and south faces dry faster).
- Immature blocks (year 0 to 3) with shallow root systems and open canopy.
- Over-tapping compounds drought stress by depleting stored photosynthates.
Effect
Field signs:
- Wilting of young leaves in immature blocks
- Premature leaf yellowing and drop out of wintering window
- Latex “pre-coagulation” in the tapping cup (latex clots before collection)
- Reduced latex flow duration (drying up within 1 to 2 hours instead of 3 to 4)
- Bark shrinkage and cracking on the tapping panel
Satellite signals
NDWI and CWSI lead NDVI by 2 to 4 weeks on closed rubber canopies. NDVI saturates on mature rubber; use it only for immature blocks or catastrophic drought.Action
1
Confirm the pattern
Cross-check NDWI/CWSI with local rainfall records. Walk the block using the Field Walk Protocol and look for wilting, pre-coagulation, and panel cracking.
2
Immature blocks: irrigate or mulch
Ring-mulch young trees with legume cuttings or EFB. If irrigation is available, prioritize year 1 to 2 blocks. Expect 20 to 40% mortality on unwatered year-1 blocks after 3 months of severe drought.
3
Tapped blocks: reduce tapping intensity
Switch from d/2 (every 2 days) to d/3 or d/4 during severe drought. Suspend stimulation (ethephon) until refoliation. Continued heavy tapping under drought is the top cause of TPD in the following season.
4
Cover the ground
Maintain legume cover crops on immature blocks. On mature blocks, leaf litter is the main mulch; do not rake or burn.
5
Monitor recovery
After rain returns, expect 4 to 8 weeks for NDWI/NDRE to recover. Latex flow recovers within 2 weeks. If flow does not recover on individual trees, suspect TPD.