How to Treat Viburnum Leaf Spot

Leaf spot is one of the most common problems in Viburnum hedges, especially Sweet Viburnum in humid parts of Australia. It appears as dark brown or black spots on the leaves, which can spread quickly through a hedge if not managed. While fungicides may help, the real key to controlling Viburnum leaf spot is prevention through correct pruning, watering, and fertiliser care.

Symptoms of Leaf Spot

Small brown or black spots on leaves, often ringed with yellow.
Leaves may turn yellow and drop prematurely.
Dense hedges with poor airflow are the most affected.

In severe cases, whole sections of the hedge can thin out, leaving gaps and reducing screening ability.

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How to Manage Leaf Spot

Leaf spot thrives in warm, humid conditions and on stressed plants. Good garden practices greatly reduce its spread:

Pruning: Trim to improve airflow and remove heavily infected sections.
Watering: Avoid wetting leaves; water at the base of the plant instead.
Hygiene: Collect and dispose of fallen leaves to prevent reinfection.
Mulching: Apply mulch to reduce splash of fungal spores from soil.

Fungicides may be used for severe outbreaks, but long-term success comes from cultural practices and strong plant health supported by fertiliser.

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Fertiliser for Disease Resistance

Well-fed Viburnum plants are far more resistant to leaf spot. Fertiliser strengthens leaves, helping them withstand infection and recover more quickly after damage. The best option is Complete Grow All Purpose Liquid NPK 20-20-20, which supplies balanced nutrients for strong foliage, root health, and resilience.

Nitrogen: Keeps leaves thick and green, reducing susceptibility.
Potassium: Improves plant defences against fungal stress.
Micronutrients: Prevent secondary yellowing and stress-related leaf loss.

Apply fertiliser every 4–6 weeks during active growth, especially after pruning away infected leaves. Feeding ensures new growth emerges healthy and resistant.

FAQ – Viburnum Leaf Spot

What causes leaf spot on Viburnum? A fungal infection that spreads in warm, humid, poorly ventilated hedges.

Can I cure Viburnum leaf spot? Severe infections require pruning and sometimes fungicides, but prevention is the most effective solution.

Does fertiliser help against leaf spot? Yes, balanced fertiliser strengthens leaves and improves resistance.

How often should I fertilise if my Viburnum has leaf spot? Every 4–6 weeks during spring and summer to maintain resilience.

Which fertiliser is best for prevention? Complete Grow All Purpose Liquid NPK 20-20-20 keeps Viburnum healthy and less vulnerable to fungal attack.