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Box Blight by Ingrid Goodbody

Published in RHSI Journal Autumn 2022

Box Blight
I live in a Georgian House in Old Connaught, near Bray. I have a garden circa one acre and a walled front garden with a pedestrian entrance. When we moved to this house in 1988 with our young family, I became interested in box hedging and planned out the front garden. I propagated all the plants from a box bush I rescued from a house in Shankill which was demolished in the early 1990s to make way for the M11. Over the next 20 years I propagated more than 130m of box and planted the front garden first
Photo 1 – View of front door with healthy box
I became inspired with the success of the box hedging and expanded into the back garden. I was aware of box blight but naively thought that as I had never used imported plants in the hedging, that my hedges were not vulnerable. Also, to my shame, I never fed the plants, and assumed my homemade compost was enough.
I have been careful to have the box cut by professionals and up to last December, 2021 all was well.
Just before Christmas, I noticed a large area of discoloured leaves on the top of the hedging leading up to the back door.
Photo 2 – View of first damaged leaves in December 2021

I immediately examined the rest of the box hedging and noticed some discolouration in other areas but it looked more like rust. I contacted the gardening advisory section available to RHS members, in Wisley, and asked for help. It was not an option to send diseased leaves and branches to the UK, but I sent photographs. One of the scientists replied very quickly to say it looked like box blight, probably Volutella buxi which is the less serious box blight and has been present in the UK and Ireland for many years. This fungus spreads in wet humid conditions and indeed we did have an exceptionally warm late autumn in 2021. Pinkish spores appear on the underside of the leaves, and are carried in water splashes to new sites. Fallen leaves carry the disease over the winter and new spores are produced in the spring. Volutella enters the plant through clipping cuts and other forms of damage to the leaves and stems.
The other box blight Cylindrocladium buxicola is more serious and has been present in the UK and Ireland since the mid-1990s. The leaves develop dark brown spots which enlarge to affect leaf tissues. Patches of greyish fungal growth appear on the underside of the leaves and spores are soon released to spread infection. Black streaks appear on the stems. The spores are capable of penetrating the leaf surface, so wounding via pruning cuts is not necessary for infection to occur. The infected leaves easily fall off the plant and the stems are typically left bare. Cylindrocladium requires moist conditions to thrive, so the spores die in dry conditions. Live spores have been found in decomposing leaves after one year, so it is important to remove any debris, burn if possible, and never put clippings on the compost heap.
From looking at the original photographs, the scientists thought there might be some evidence of caterpillars of the moth Cydalima perspectalis. It was thought by enlarging my photos, that there might be evidence of chewed leaves. I could find no caterpillars and was most distressed at this point having watched Monty Don in the gardens of the Adriatic, where the wonderful ancient parterres of box have been totally devastated by the caterpillars defoliating the plants.
I was advised that the way to deal with this disease is to remove the box hedging and replant with something else. However, I found it difficult to even think of destroying twenty years of work so I decided to try to manage the disease.
It is difficult to completely eliminate box blight, but it is possible to reduce the impact of the disease with good management.
The priority is to remove as much inoculum (infected material which could be carrying spores) from the hedge as possible.
My most infected hedge was removed and as I cannot burn material, it was sent off to the council green waste facility Green King on the way to Gorey, where the temperatures are extremely hot, and will kill off any spores.
The rest of the hedging was cut by 1/3, to healthy tissue, by professional topiary cutters, with sharp sterilised clippers. This removes the inoculum, and also creates a more open structure. All the cuttings were removed from the centre of the hedge which was now very bare, and from underneath as well. This was a monumental job and very hard on my hands and arms. It was advised to sterilise clippers and secateurs between use on healthy and diseased areas. This should be carried out in dry conditions. Clothes should be washed immediately.
Photo 3 – View of most damaged hedge which was removed

It is advised to reduce humidity in box hedging by removing overhanging vegetation, and not applying overhead watering.
I used TopBuxus health mix which is a foliar feed and can be used frequently during the year March to December
I used TopBuxus XenTari as a foliar spray against the Box moth caterpillar. It is indicated three times a year to coincide with the moth laying the eggs and the eggs hatching. It is a biological insecticide and contains a natural potent strain of Bacillus thuringiensis which controls the caterpillars. It is not harmful to humans, wildlife or beneficial insects such as bees for pollination, or insect predators. I also got Pheromone traps for the moths which are indicated in May, and end of July.
The cut box hedging has recovered amazingly well and all the cut bare stems in the middle have healthy new growth. I have found no moths in the Pheromone traps. I have found no caterpillars so far.
Photo 4 – View of regeneration of growth after the hedge was cut by 1/3

But … after the extremely wet weather we had at the end of the dry spell from July to August 2022, I have noticed some discoloured leaves again now in mid-September, which is discouraging.
I have been advised not to have the hedge cut again until the Spring by the RHS gardening advice section to give the recent regrowth time to mature.
Photo 5 – Encouraging growth over the summer in the front garden
I have been actively looking for alternatives to Buxus sempervirens but have found nothing which can compare. I have another box hedge of a different species, which has a more open growing habit, and can be moved to the front garden if necessary if my management of the present box does not work. I know there is a section in Wisley where there are trials on alternatives to box, and I hope to go over there myself in the Spring.
I hope this has been of some use to those of you who are quaking in your boots at the prospect of your beautiful box hedges and topiaries succumbing to diseases of box. Box blight can be managed fairly successfully but is it worth the scratches, effort time and expense?
The jury is out!!!

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