Corynespora Leaf Fall is, along with powdery mildew, one of the most dangerous leaf diseases affecting rubber trees.
It causes serious yield losses in both mature (tapping) and immature (establishment) plantations across major rubber-growing regions in Vietnam.
Symptoms and Identification
Table of Contents
The disease is caused by the fungus Corynespora cassiicola (Berk. & Curt.) Wei, which infects rubber trees at all growth stages and occurs year-round.
In Southeast Vietnam, two major outbreaks typically occur:
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Late May – early June
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Late August – early September
The disease is particularly severe on susceptible clones such as RRIV 3 and RRIV 4.
It can attack leaves, petioles, and shoots, causing death of nursery seedlings, lowering grafting success rates, and leading to defoliation and dieback in plantations.
When the infection is prolonged, it results in growth retardation, reduced latex yield, and in severe cases, tree mortality.
Disease Symptoms
On Leaves
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Circular gray to brown lesions surrounded by yellow halos.
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Sometimes the center of the lesion becomes perforated (holes).
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Infected young leaves curl, deform, and fall prematurely.
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On certain clones, lesions form fishbone-like black streaks along leaf veins.
Under favorable conditions, lesions expand, turning leaves yellow or orange before defoliation.
On Shoots and Petioles
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Longitudinal cracks appear on shoots and petioles, exuding latex that later blackens.
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Lesions can extend up to 20 cm, causing shoot dieback or even plant death.
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In the wood beneath lesions, black streaks are visible.
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On petioles, small black cracks (0.5–3.0 mm) appear, leading to leaflet drop while still green, even when the leaf blade shows no visible symptoms.
Prevention and Control Measures
1. Fungicide Treatment
Use one of the following fungicides and concentrations:
| Active Ingredient | Example Products | Concentration |
|---|---|---|
| Tebuconazole | Vitebu 250SC | 0.05–0.06% |
| Hexaconazole | Hexin 5SC, Anvil 5SC, Vivil 5SC, Saizole 5SC | 0.2% |
| Pyraclostrobin | Headline 250EC | 0.02% |
Add sticking agent BDNH 2000 at 0.2% concentration to improve adhesion.
2. Application Guidelines
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Nurseries, budwood gardens, and immature plantations:
Spray evenly on young shoots and leaves every 7–10 days, preferably in the morning when the air is cool and humidity is high. -
Mature (tapping) plantations:
Start spraying when the infection is light (level 1–2) or when 3–5% of young leaves begin to fall.
Focus preventive spraying during May–June and August–September in Southeast Vietnam, especially for susceptible clones RRIV 3 and RRIV 4. -
Use high-pressure sprayers to cover the entire canopy and young shoots.
Stop spraying when sunlight becomes intense (around 10:00–10:30 a.m.).
Apply 2–3 treatments, each spaced 7–10 days apart.
3. Cultural and Nutritional Management
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Reduce or suspend latex tapping during severe infection to help tree recovery.
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Fertilize adequately, following technical recommendations.
Where possible, increase potassium fertilizer by 25% to strengthen plant resistance. -
Collect and burn infected leaves and twigs during leaf fall season to destroy fungal spores.
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Inspect plantations frequently, especially during weather transitions (from rainy to dry season).
Summary
Corynespora Leaf Fall is a serious and recurrent disease in Vietnam’s rubber plantations.
Effective management requires an integrated approach combining:
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Resistant clone selection,
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Timely fungicide application, and
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Proper fertilization and sanitation practices.
By taking preventive action early — particularly during known outbreak periods — growers can maintain tree health, stable yields, and sustainable rubber production.