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Powdery mildew (Oidium heveae) attacks rubber during the refoliation window immediately after wintering. It kills young leaves as they emerge, prolonging the annual NDVI dip by 2 to 4 weeks and causing repeated flush loss. Most damaging in northern Peninsular states (Kedah, Perlis, Perak) where wintering coincides with cool, misty mornings.

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Cause

  • Cool nights (< 22 C) with misty mornings during refoliation (Feb-Apr)
  • Susceptible clones: RRIM 600, some PB clones
  • Northern states with more pronounced dry-cool wintering
  • Highland blocks (> 300 m elevation)

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Effect

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Satellite signals

A slow post-wintering recovery in northern states is the diagnostic satellite signal for powdery mildew.

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Action

1

Confirm on new flush

White powder on the underside of expanding leaves confirms Oidium heveae.
2

Fungicide sprays (timing-critical)

Begin sprays at start of refoliation (first sign of new flush). Late sprays are ineffective.
  • Sulphur dust (30 kg/ha via mist blower), 3 to 5 rounds at 7 to 10 day intervals
  • Alternative: hexaconazole or triadimefon
Northern states typically require the full 5-round program in outbreak years.
3

Adjust tapping

Do not resume tapping until the second flush is fully expanded. Premature tapping on partially-refoliated trees causes long-term yield loss.
4

Long-term: clone selection

On chronic northern blocks, favor mildew-tolerant clones at replanting.