Box Blight Treatment

Box blight can cause browning leaves and rapid dieback in box hedging. Learn how to spot it early, treat it effectively, and reduce future outbreaks in this box blight treatment guide.

By Alistair Fuller

What is Box Blight?

Box blight is a fungal disease affecting the leaves and stems of box plants, or Buxus. It is caused by two closely related fungi, Calonectria pseudonaviculata and Calonectria henricotiae, previously known as Cylindrocladium buxicola.

The disease causes brown leaves, leaf loss, black streaks on young stems and bare or dying patches. It can spread rapidly in warm, wet and humid conditions through infected leaves, rain splash, tools, clothing and newly introduced plants.

Box blight should not be confused with Volutella blight, a separate disease that can produce pink fungal growth, or box tree caterpillar, which causes chewed leaves, webbing and visible caterpillars.

Image rights: Wikimedia Commons License

Fungal pathogens, or disease spores, can take only a matter of hours to infect leaves. Disease is spread by wind and rain-splash and also carried on infected garden tools.

How to Treat Box Blight

Box blight is best treated by removing infected growth and fallen leaves, disinfecting tools, improving airflow and, where appropriate, applying an approved fungicide. Fungicides cannot restore dead leaves or branches, so they should form part of an integrated box blight treatment programme rather than being used alone.

A fully integrated approach for Box Blight treatment should include:

1. Fungicides

Products such as Signum and Nativo 75 WG give good results on box blight with protectant and curative properties. Application rate, timing and correct product selection is key to delivering the best results. These fungicides are approved under an “Extension of Authorisation for Minor Use”, which is a different method of approval requiring some documentation for the applications to be compliant and legal. We can assist customers with the appropriate advice.

2. Biostimulants

This type of product works differently from a fungicide, but stimulates a plant to withstand and recover from disease infection. Biostimulants can also reduce the reliance on traditional fungicides, reducing the risk of disease resistance forming.

3. Fertilisers

A. Granular Fertiliser - Ensuring box hedging has the correct macro nutrition will aid recover of damaged plants. Our classic tree and shrub fertiliser Arbor Gold is a once per season application (typically Spring), delivering the correct balance of nutrients for hedging in a slow-release form.

B. Foliar Seaweed - In-season applications of seaweeds and trace elements will ensure a hedge has the full complement of nutrients to speed up damage recovery and minimise in-season growing stress. Products in this category include Phyter, Maxicrop Original and Amvista L9 Seaweed. For ease of applications, these products can be safely tank-mixed with our approved fungicide, bio-stimulant and caterpillar suggestion (below).

4. Minimising Disease Spread

Good hygiene is paramount for successful box blight treatment. Any equipment that contacts a hedge should be disinfected before use. This includes secateurs, shears and powered hedge trimmers. Our popular arboricultural disinfectant is Propellar, available in 1L ready-to-use bottles or larger 5L containers.

5. Other Pests

Once you have invested in a box blight treatment programme, it is imperative the hedge does not suffer from further setbacks. One common issue that can be encountered is damage from Box Caterpillar. This pest can decimate the foliage of a hedge, reducing the chances of recovery from box blight.

This issue can be avoided by the inclusion of an inexpensive, natural and highly effective biological caterpillar control product, such as Dipel DF.

Important Notes

Damp and blustery periods of weather are very conducive to disease spread, and it can infect at any time of the year throughout most of the UK.
Mild winters have extended to the traditional box blight season.
Collect fallen leaves from all plant species in the vicinity regularly and remove dead plants, then burn... DO NOT compost.
Water during dry weather using drip tubes rather than spraying the foliage. Alternatively, you could soak the soil (not foliage) once a week rather than sprinkling multiple times a week.
Some varieties of Buxus seem to withstand infection better than others. Unfortunately, the most popular variety, Buxus sempervirens 'Suffruticosa', seems to be the most susceptible to disease.
Newly purchased plants (Buxus or otherwise) should never be planted straight away near box to reduce the importation of infection. Keep new plants in ‘quarantine’ for a short period to observe any signs of disease development.

If you have any questions about box blight treatment or any other problem your outdoor spaces might be suffering from, don't hesitate to contact our team of experts for free, bespoke advice.

Frequently Asked Questions

What does box blight look like?

When your box plants have box blight, you will see that your leaves have gone brown and begin to fall off. Other symptoms you might spot are black or striped stems.

How can you prevent box blight?

You can prevent box blight by ensuring your plants are not overcrowded and have a good circulation of air. Warm and damp conditions are a way in which box blight can set in.

What is the most effective box blight treatment?

An integrated approach, combining fungicides, biostimulants and fertilisers, is best for effective box blight treatment. Reliance on just one method of control can easily lead to disease resistance forming and disappointing results.

Can box plants recover from blight?

Yes, box plants can recover from box blight if enough healthy growth and living stems remain. Remove infected growth and fallen leaves, improve airflow and support recovery with moderate feeding and appropriate watering. Severely or repeatedly affected plants may need to be removed.

How can I tell the difference between box blight and box tree caterpillar?

Box blight causes brown leaves, leaf loss and black streaks on stems, while box tree caterpillars leave chewed foliage, webbing and droppings. Part the foliage and inspect the plant closely. Visible green and black caterpillars or eaten leaf edges indicate box tree caterpillar rather than fungal box blight.