Trouble with Buxus

A friend with a garden maintenance business rang recently to discuss buxus blight. This is a fungal ailment which attacks box plants. It was first found in New Zealand in 1998 and has been a problem in Auckland for some time. Buxus being an infinitely useful but deathly dull plant, we made contingency plans early, in case the fungus ever struck our modest metreage.

I have just paced out our box hedging and we only have around 25 metres of it plus one established topiary, so it does not exactly feature large in our garden. From the start, we figured that buxus did not warrant spraying to keep it healthy so we have always been ready to rip the plants out and burn them if necessary. We have alternatives out the back, so to speak, so taking out the buxus hedges was only ever going to be a minor inconvenience.

But Garden Maintenance Friend was horrified when I suggested he advise his clients to rip out their box hedging and replace it with something which does not get blight. Most of them have a great deal more than 25 metres and do not have the advantage of alternative plants for instant replacement. He suggested he would far rather I write a column on the topic and that his clients may take the advice better from the newspaper than from him.

The bottom line is that if you have buxus blight (or fungus cylindrocladium) in your garden, you have a problem and if you don’t do something about it, it will spread rapidly. Doing something about it is easier said than done in this day and age when a severely restricted range of chemicals is available to the home gardener. There are no heavy duty fungicides that can be bought over the counter unless you have a spray certificate. Which means that if you want to go the spraying way, you will have to employ a certificated operator. But we are also strongly of the view that gardeners should take more responsibility for their actions and that spraying a utility plant like buxus is simply unjustifiable. It is time we asked many more questions about the spraying practices which have become the norm in this country over the last four decades.

There appear to be three main ailments that hit buxus and if you have plants which are looking poorly, it may not be the dreaded blight. A dead patch in one area just above the ground is most likely to be animal urine – territory marking by dogs or a tom cat. I am not at all sure how you stop the offending animals, but it is no reason to rip out your plant.

Zephyr the dog treats the buxus hedge with some contempt.

Zephyr the dog treats the buxus hedge with some contempt. (Photograph: Abbie Jury)

There is a pinky mildew (called volutella buxi) which has been around a long time. It disfigures the plant but is not usually fatal. It takes hold in wounds so if you clip your hedge hard, it is likely to be more apparent soon after. Healthy plants can outgrow volutella so a bit of effort may retain your hedges.

The dreaded buxus blight has cut a swathe through the United Kingdom’s millions of box plants since the mid nineties, through Auckland’s since the late nineties and is likely to be the cause of dying buxus reported in Taranaki. It is the problematic one. It starts as dirty dark spots on the leaves and black streaks on the stems and spreads rapidly, causing the plant to lose all its leaves and usually die. It often shows up initially as dead patches along the top whereas the sides will appear to be fine. Research has shown it takes only five hours to start multiplying so if you ignore it, it may well surprise you by how fast it takes hold. It is impervious to cold (most fungi prefer warm, moist conditions) which is why it has taken hold in the UK. This means it does not slow down in winter. It is only very dry conditions which it dislikes and as most of Taranaki is humid most of the year, we have splendid conditions for it. Being a fungus, it increases from spores so it can be airborne which means that if you live in town and your neighbours have it, sure as eggs you will get it too. And as the spores survive in decomposing leaves for a year, it is nigh on impossible to eradicate. You may burn the offending plant (avoid the compost heap for this one) but you are not going to be able to pick up every dead leaf. You also need to disinfect all tools which have been in contact with it – household bleach apparently works.

Prevention is better than a cure. There is a tendency for owners of buxus hedges to cut them hard twice a year and, ever obliging as they are, they sprout afresh. But over a period of years, the hedges get increasingly dense as well as being filled with dead leaves which sit in the middle. I was a bit surprised when I overheard a buxus expert holding forth recently on the need to thin out buxus hedging and topiary shapes and to vacuum out the accumulation of dead leaves. Really, I thought. But she is right. And if you want to reduce the chances of getting a terminal case of buxus blight, you may like to head out now with the nippers, the clippers, the secateurs and the blower vac. Some good hygiene, housekeeping and air movement will reduce the chance of blight getting hold. But it is not a cure and personally I am not so enamoured of buxus that I think it justifies that sort of effort.

I am told that two sprays of copper a week apart with a wetting agent added can help, even cure it, so if you have affected plants you may like to try this approach. Mark is surprised that copper, which is anti bacterial and not a fungicide, could be so effective. And the information from the UK where buxus blight has been extensively researched, certainly does not bear out the copper theory. If copper is working here, it is unlikely that we have found a wonderfully simple solution and are therefore cleverer than our overseas colleagues. It is far more likely that the cause is not in fact fungus cylindrocladium. That said, it is worth a try if the alternative is the drastic step of total replacement.

If you have to rip out your buxus, burn it all. And don’t replace with more buxus. You will need to be looking to some of the alternatives that clip – coprosma, camellia, teucrium, corokia or the like. There are no species of buxus that are resistant to cylindrocladium. The fungus does not reside in the soil so treating the soil or replacing it is a waste of effort. It is the plants that are the host.

Sadly, for owners of buxus hedging, there does not appear to be any good news as far as fungus cylindrocladium goes. The only good news overall is that it may curtail the slavish use of buxus as hedging and edging in every second garden.