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Black stripe (also called black thread or panel Phytophthora) is caused by Phytophthora palmivora or P. meadii attacking the tapping cut. Wet, warm weather combined with poor tapping cuts creates the entry point. Once established, vertical black streaks propagate down the panel, destroying the cambium and permanently reducing yield.

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Cause

  • Wet weather at tapping (rain within hours of tapping)
  • Deep or ragged tapping cuts (bark wounds beyond the cambium)
  • Dirty tapping knives (pathogen spread from tree to tree)
  • Tapping in the early morning during wet season (spore-rich conditions)
  • Poor panel hygiene (mud splash, no wound protectant)

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Effect

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Satellite signals

None. Black stripe is a tree-level disease diagnosed at the panel during tapping rounds.

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Action

1

Scout every tapping round

Tappers should visually inspect the panel below the cut on every round. Any vertical dark streak should be flagged immediately.
2

Suspend tapping on affected trees

Stop tapping the affected panel. Continued tapping spreads the pathogen down the panel and to neighboring trees via the knife.
3

Apply wound protectant fungicide

Paint the panel with metalaxyl (Ridomil) or fosetyl-Al paste around the cut. Repeat weekly for 4 weeks.
4

Sanitize tapping knives

Dip knives in fungicide or bleach between trees during outbreaks. Train tappers on proper cut technique.
5

Panel switch

On severely affected trees, rest the panel and switch to the next tapping panel segment at the next tapping cycle.
6

Prevent in wet season

Do not tap when trees are wet (rain within 4 hours). Prophylactic fungicide painting during monsoon on high-risk blocks.