Rubber plantations in Vietnam are facing increasing challenges from fungal and physiological diseases affecting both the tapping panel and root system. These conditions reduce latex yield, weaken tree health, and shorten the economic life of plantations.
This article summarizes three major diseases — Stripe Canker, Tapping Dryness, and Brown Root Disease— including symptoms, causes, and treatment strategies.
1. Stripe Canker on Tapping Panel
Table of Contents
Causal Agent
Caused by fungi Phytophthora palmivora (Bult.) Bult and P. botryosa Chee.
Distribution and Conditions
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Common in humid, rainy regions with low temperature and high moisture levels.
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Most severe in areas with poor drainage or prolonged rainfall.
Damage
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The fungus destroys the tapping surface, including regenerated bark and original bark, leading to loss of latex-producing area.
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In severe cases, latex yield can drop by up to 100%.
Symptoms
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Early stage: small vertical brown streaks appear slightly sunken along the tapping cut.
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Later: lesions expand into large, soft, rotting patches exuding yellowish, foul-smelling latex.
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Black stripes appear on the wood beneath, and the cambium tissue is destroyed.
(See Figure IX.10)
Treatment
Indirect control:
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Avoid tapping when the panel is wet.
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Follow proper tapping techniques to prevent bark damage.
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In rainy seasons, reduce tapping frequency or suspend tapping temporarily.
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Use rain guards or protective covers for tapping cuts.
Direct control:
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Apply Metalaxyl 0.35% (3,500 ppm) + 1.0% adhesive on tapping cuts.
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Paint a 1–1.5 cm wide strip above the tapping line after latex collection.
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Preventively apply once a month during the rainy season.
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Infected trees: treat every 10 days until lesions heal.
2. Tapping Dryness
Causal Factors
A physiological disorder, not caused by pathogens.
Triggered by:
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Over-tapping (excessive latex extraction),
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Nutrient depletion, or
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Genetic sensitivity in individual trees.
Distribution
Occurs widely in commercial rubber plantations, occasionally even in untapped young trees.
Damage
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Leads to temporary or permanent latex flow stoppage.
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Reduces productivity both immediately and long-term across the plantation.
Symptoms
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Initially, latex flow ceases on part of the tapping cut.
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Premature latex coagulation appears on the panel.
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The inner bark turns light to dark brown and becomes dry and cracked.
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Cracks spread downward or upward from the tapping line.
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Despite no external leaf symptoms, the tree canopy remains green and normal.
Two types are observed:
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Total dryness: entire panel becomes dry and cracked.
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Partial dryness: only short sections affected; trees may recover after rest.
Treatment
Prevention:
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Tap according to standard frequency and depth.
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Apply adequate fertilizer and follow stimulant use regulations.
Management:
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No effective cure currently exists.
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If over half of the tapping line produces no latex, stop tapping for 1–2 months.
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Resume tapping at reduced intensity after recovery.
3. Brown Root Disease
Causal Agent
Caused by the fungus Phellinus noxius (Corner) G.H. Cunn.
Distribution
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Common in replanted areas or former forest land rich in woody roots.
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The pathogen survives on old stumps and root debris, infecting new rubber roots.
Damage
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Causes root decay and eventual tree death.
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Particularly harmful to replanted plantations without proper soil sanitation.
Symptoms
On foliage:
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Leaves become small, pale green-yellow, drooping downward.
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Lower branches defoliate, followed by total canopy collapse and death.
On roots:
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Infected roots are covered with dense fine rootlets and thick soil coating (3–4 mm).
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After cleaning, the outer root turns yellow-brown, with black-brown wood streaks that easily crumble.
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Fungal fruiting bodies often appear near the base of the trunk — a key diagnostic sign.
(See Figure IX.11)
Treatment
Prevention:
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Remove all root debris before replanting.
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In high-risk areas, mix 100–150 g of sulfur powder into planting holes 5–7 days before planting.
Control:
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For infected trees and nearby plants:
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Drench the base with Hexaconazole 0.025% (250 ppm) solution, 3–5 liters per tree, within a 0.5 m radius.
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Repeat 2–3 times, every 2 months.
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For dead trees:
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Cut stumps 10–15 cm above ground, and paint with Triclopyr 1.25% (12,500 ppm) in diesel oil,
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or dig out and burn all roots to eliminate inoculum.
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Conclusion
Effective management of tapping panel and root diseases requires strict hygiene, balanced fertilization, and adherence to tapping standards.
Combining preventive fungicide application with environmental sanitation helps maintain sustainable latex yield and plantation longevity.