Corynespora Leaf Fall (CLF) in Rubber

Corynespora cassiicola: the major economic leaf disease of Malaysian rubber, especially on susceptible RRIM 2000 clones. Recognition, out-of-season detection, and fungicide protocols.

Corynespora Leaf Fall (CLF) caused by Corynespora cassiicola is the major economic leaf disease of Malaysian rubber. It has caused replanting decisions on entire estates due to clonal susceptibility (particularly RRIM 2005, RRIM 2020 series, and some PB clones). It causes out-of-season leaf fall that satellite systems can detect as a delayed or failed wintering recovery.

Cause

• Susceptible clones: RRIM 2005, RRIM 2020 series (some), some PB clones
• High humidity and warm temperature (> 25 C, RH > 80%)
• Continuous rain especially during refoliation window
• Weakened trees from drought, TPD, or over-tapping
• Adjacent infected blocks (windborne spore spread)

Effect

Stage	Symptom
Early	Small brown-black spots (2 to 5 mm) with yellow halo on leaves
Mid	Spots expand, coalesce; large brown lesions with characteristic “fishbone” or “railway track” veinal pattern
Late	Whole-leaf blight, defoliation
Terminal	Repeated leaf fall in the same season (secondary leaf fall), depleted photosynthesis, latex flow drop

On susceptible clones, CLF causes 2 to 4 waves of leaf fall per year outside the normal wintering window, seriously depleting tree reserves.

Satellite signals

Index	What to watch	Threshold
NDVI	Drop outside normal wintering window (Feb-Apr)	-0.10 sustained
Anomaly view	Delayed or failed refoliation	Compare vs prior year
Repeated dips	Multiple NDVI drops in same year on same block	Multiple crossings

CLF is one of the strongest use-cases for satellite monitoring because it manifests as out-of-season canopy loss visible from space.

Action

1. Confirm in the canopy

   Look for brown-black spots with yellow halo, and the diagnostic railway-track pattern on lesions. Send samples to MRB for confirmation.

2. Identify the clone

   Confirm clone from block records. RRIM 2005 and known-susceptible clones require aggressive spray program; tolerant clones may only need monitoring.

3. Fungicide spray program

   For young immature trees where spraying is feasible:

   • Mancozeb or propiconazole, 2 to 3 sprays at 14-day intervals during refoliation

   For mature trees, spraying is generally not economic; management shifts to clone replacement at replanting.

4. Reduce tapping intensity

   During heavy CLF episodes, cut tapping frequency to allow refoliation. Continued heavy tapping accelerates canopy exhaustion.

5. Long-term: clone replacement

   At replanting, avoid known-susceptible clones on high-CLF sites. Consult current MRB planting recommendations.

Recommended alert settings

Trigger	Condition	Severity
Out-of-season NDVI drop	-0.10 sustained 14 days outside Feb-Apr window	High
Delayed refoliation	NDVI failed to recover by 10 weeks after wintering	High
Susceptible-clone alert	Any NDVI dip on flagged clone block	Medium
Weather trigger	RH > 80% + rain > 100 mm/week during refoliation	Medium

Related

• Pestalotiopsis leaf fall
• Powdery mildew
• Rubber ecosystems (wintering baselines)
• Rubber Diagnosis