Earlier on this year, unfortunately, box blight was identified in one of the gardens we work in.
Box blight is a fungal disease affecting box (Buxus). There is no cure for it. Its spores are dispersed in water, and it can be spread by wind-blown rain, as well as by animals and human activity.
There are two fungi which cause box blight: Cylindrocladium buxicola (syn. Calonectria pseudonaviculata) and Pseudonectria buxi. These are often found together. Although it is mainly Box (Buxus) that is affected in this in this country, Cylindrocladium buxicola can affect other members of the Buxaceae family, which includes Sarcoccocca and Pachysandra. Pseudonectria buxi only affects Box, (Buxus).
Plants are often sprayed with fungicides (triazoles), by nurseries and sellers, but this only suppresses the disease, it doesn’t cure it, so the infected plant will succumb to it eventually, and, in the meantime holding on to an infected plant will risk spreading the disease to other plants. An infected plant would have to be repeatedly sprayed at regular intervals, which can lead to an accumulation of chemicals in the soil and surface water, with the potential to adversely affect wildlife. Some of the chemicals used can be toxic to birds, can disrupt the reproductive abilities of animals, including humans, can target the liver and blood system in humans, cause eye irritation, and more research needs to be done to discover whether they are carcinogenic. Side effects experienced by workers exposed to chemicals include skin rashes, allergic dermatitis, itchiness, nausea, headaches, diarrhea, abdominal pain, vomiting, and nosebleeds. Also, the effectiveness of spraying differs according to which of the fungi is causing the blight. C. buxicola is divided into two genetic types, which have different levels of sensitivity to fungicides.
The symptoms of box blight include leaves turning brown, bare patches and leaf fall. Plants can be affected at any time of year, but the disease is more active and likely to spread in the rainy season. Once a plant has been affected, it can spread very rapidly throughout the garden, decimating box hedging and topiary. C. buxicola also turns young stems black and causes die back.
There are no disease resistant varieties available, but, the plant’s susceptibility to the disease can be reduced by less frequent clipping. Frequent clipping creates dense foliage; reducing this can help to create more air-flow through the plant, which makes it less susceptible to disease. P. buxi requires a wound to get into the plant, so reducing the amount of clipping means less opportunity for it to get established. However, C. buxicola does not require a wound, and can be far more lethal. Overhead watering should also be avoided.
New plants from nurseries, should be kept in isolation for three weeks to allow time for any suppressed disease to show.
However, once signs of the disease have been spotted, it is important to act immediately to avoid its further spread. The only thing to do is to dig up and burn all infected plants. The disease can remain on fallen leaves for at least six years, so it is important to clear up all the fallen leaves, and, although it doesn’t stay on the soil particles themselves, it is advisable to replace the first layer of soil, as it may contain fallen leaves and plant matter which harbour the disease.
This is what we did in the garden we found the box blight in. We also thoroughly disinfected all the tools we used, disinfected our boots and washed all our clothes. As an extra measure, we also wore disposable overalls over the top of our clothes. That way, we ensured we didn’t spread the disease from one garden to the next.
The box blight was spotted on one hedge in the garden, and, as we acted quickly, so far, it hasn’t spread to the other hedges, but we are being vigilant about keeping an eye out for it, as, acting quickly is the key to halting its spread. It may still be present in the garden on fallen leaves that have been missed (the box hedging was next to a gravel path, and unless we dug out and resurfaced the whole of the gravel path, it would be very difficult to collect all the leaves which had fallen between the stones). It survives as resting structures (mycelium), and will produce spores when the conditions are suitable, so we may find the other plants in the garden succumb at any time.
Replacing the hedge with new box plants was not an option, because of the likelihood of the disease still being present in the garden. In this instance, we chose to replant with Rosemary – the cultivar we chose was Rosmarinus officinalis ‘Primley Blue’, for its upright habit and suitability for hedging. There are quite a few options available when replacing box hedging, including Yew, Lavender, Lonicera nitida (shrubby honeysuckle), Ilex crenata (Japanese, box-leaved holly), Hebe cultivars, Santolina (Cotton Lavender), Potentilla, and Berberis cultivars. One option we also considered was using step-over apple trees as a hedge alternative. Low level hazel hurdles or fencing is also an option, and less formal divisions within gardens can be created using ornamental grasses, Hydrangea, Nepeta, Perovskia or Salvia, though perennials wouldn’t provide structure in winter, which is one of the important qualities that makes box hedging a popular choice. However, the demise of a box hedge need not be viewed with despair, it can be approached as an opportunity for creating something new and different in the garden. If you have suffered with box blight and are looking for someone to help you deal with it, or choose a suitable replacement, please contact us, and we would be happy to discuss it with you.