We are all looking forward to what is hopefully a lovely spring. After the heavy rain over the winter, at last the weather is warming up nicely. Plants of all sorts are bursting forth with new growth, colour and a hope for a lovely summer. But spare a thought for one group of plants that have suffered more than most from the weather and they are the humble box. As with all the wet weather the cases of box blight has risen dramatically.
Box or Buxussepervirens is an essential part of many gardens as it gives it structure that is there all year round. Many formal gardens depend on clipped compact shapes to provide interest and as a foil for other planting. Low box hedging for many years have been used for parterre, knot gardens and as edging to the beds in kitchen gardens. But sadly for how many more years will this be the case as many owners have to remove dead or dying plants. Some of those have been there for centuries and even though it gives you the chance to renovate or change an area, it is changing or ruining many garden landscapes.
The disease was first noticed in 1994 on a Hampshire nursery. Since then it has spread all over the country, and is now Europe wide with reports of the disease showing up in the USA and New Zealand. In the late 90s the RHS started doing research from pieces of box sent in by many of its members. Up to now there is no known cure for the disease, only cultural controls that gardeners can do to help stop the spread. The disease is caused by two pathogens, Cylindrocladiumbuxicol and Voluttabuxi. Both of which are spread by water droplets in the air, and as the spores are sticky they are easily carried by animals and humans both on their clothes and on tools such as hedge cutters, shears and pruners. They are known as cold diseases as they are not affected by frost and are only suppressed in temperatures above thirty degrees. With the early stages of the disease being easily missed, it is often only noticed when the plant starts to die back particularly on the top of plants that are cut into a hedge, whilst the sides are often still green. The first stage is the attack of the plant by the Cylindrocladiumbuxicol pathogen this causes the leaves to have dark brown spots and spreads in a spiral fashion, and the stems have blackened lines on them. This eventually causes the leaves to turn a tan or straw colour, by which time the leaves are dead. This fungus attacks the plant very quickly with germination of the spores happening during the first three hours with total penetration occurring after a further five hours. The plant is then attacked in most cases by Voluttabuxi, as this is a pathogen that attacks damaged foliage. This shows up on the leaves as a pinky coloured powdery mildew like infection. Even though in itself it is not a big problem, but when combined with the first fungal attack it proves, in most cases, deadly to the plant.
Box in gardens are mostly planted as hedges, and alternatively as clipped shapes such as balls, spirals, or more exotic shapes. The fact they are heavily clipped shapes helps the disease take hold, as to help prevent blight taking hold you need to let more air into the centre of the plant. So you need to clip your plants less than normal which of course spoils there shape, and when you do cut your plants don’t do it on a warm damp day. Also it is very important to keep your cutting tools clean to stop infecting fresh plants. You can do this by dipping your tool blades into a solution of bleach or other kitchen disinfectants, of course diluted to rates as stated on the container. When you have finished cutting make sure you clean up all debris as this will contain spores ready to re infect. In bad areas it may be advantageous to even remove the top half an inch of soil to make sure all spores are removed, and replacing with fresh soil. Of course stripping off all infected foliage that hasn’t fallen yet and the dead growth inside the plant also helps, these are easily noticed as they will be a straw or tan in colour. All clippings and dead growth removed from the plant should not be composted but should be burnt straight away. As said before there is no known chemical cure for this disease but if you use a copper based fungicide with some contact action you can help hold the attack or at least slow its progress. Combined with this keep the plants well fed and growing strongly, as this along with other infections find it harder to attack strong growing plants.
Remember the conditions that cause the disease to spread quickest is damp, poor air circulation and shade. So when planting new plants place them in an area that is in full sun, as shade keeps the foliage damp. When establishing new plants do not use sprinklers to water plants but use seep hoses at the base of the plants. But prevention starts before you get home, as many nurseries have stock of box that have the blight already in the plant. As the plants have been sprayed with fungicide within their growing process, and even though this doesn’t cure it help suppress the disease. So check all plants with great care, if you notice leaves have dark markings on them discard these and remember all plants within that batch may be infected. Since the outbreak of box blight and the public’s awareness of this disease the sale of box has dropped to almost half of what it was ten years ago. But luckily the sales of alternative types of plants have increased to balance.
There are many alternatives to box and they include the following types-
Loniceranitida a dense bushy small leaved plant that is good for small hedges and topiary, as it can be kept clipped tightly. Not good for very windy or boggy sites but will be happy in shade. If you like colourful hedges choose “Baggassens Gold” with yellow foliage.
Griselinia is a shrub with soft glossy lime green leaves, which does best in full sun on light well drained soils. It is also very good in coastal areas as it is salt tolerant. Can’t be cut as tight as other types but still makes a beautiful hedge.
Taxusbacata or yew is another plant popular for topiary and hedging. It has dense evergreen foliage that stands heavy close clipping. Can be grown on many soil types and situations but avoid very waterlogged soils.
Ligustrum or privet is a good hedging plant which even though is classed as an evergreen it may lose some leaves during a harsh winter but grows back quickly in the spring. It has been a popular plant for hedging for years as it is good for areas that suffer from pollution.
Laurusnobilis or bay has aromatic glossy green leaves that are a popular choice for topiary and hedging.
Ilex crenata which is a true alternative to box and to most it is hard to tell apart, and even though it’s a holly it’s certainly not prickly. It grows the same as box and can be clipped into many shapes but doesn’t suffer from blight or leaf scorch in summer.
Euonymus which are evergreen and very good for windy cold situations. The two varieties most popular are Emerald Gaiety with cream edges to foliage and Emerald and Gold which has yellow markings on the leaves.