Box hedge diseases: symptoms & treatment
Unfortunately, it is not only the box tree moth that affects the box tree. This is our guide to the most common box tree diseases and their treatment.
The box tree (Buxus) can be found in almost every garden and park. Sadly, it is often in peril due to pests and diseases. As a result, its wonderful leaves often discolour and its ornamental value drops drastically. We have summarised all important Information relating to the different diseases.
Box tree diseases
It is not just people who become ill but also our shrubs can get a disease of some kind. In the following, you can find an overview of the common box tree diseases and how to keep them in check.
Boxwood blight or boxwood leafdrop
The boxwood blight has been present in Europe since 2004. This aggressive fungal disease can be recognized through brown spots on the leaves and dark stripes on the shoots. Especially in humid and warm summers, gardeners have to deal with this box tree disease.
Causes and symptoms of boxwood blight
The disease is not only known under the name boxwood blight, but is also called boxwood leafdrop. It is caused by the fungus Cylindrocladium buxicola and has been bringing gardeners in Europe to the brink of despair for almost 15 years. This pathogen is capable of infecting completely healthy box bushes and causing damage even to them. The optimum conditions for an outbreak of this disease are temperatures around 25 °C and five to seven hours of the leaves staying wet. It usually takes place in July or August and the first symptoms appear after about two weeks, but the damage only becomes apparent in autumn. The fungus can survive in the soil or on fallen leaves. It can re-infect the plant from the soil for up to eight years.
But what are the concrete symptoms of the boxwood blight? First, brownish-orange patches appear on the leaves, which will grow bigger and bigger. The edges of these patches are usually darker in colour, and half of the leaf surface often turns brown. Black stripes are then visible on the box shoots. The shrub then loses the leaves, but fortunately the shoots remain green and can sprout again. On the underside of the leaves, a white spore covering can often be seen in damp weather. What is particular is that the young leaves are often affected. Older leaves, on the other hand, are rarely infected. If the box tree is afflicted frequently or if it is additionally weakened by frosts, the shoots can die. The shoots also show dark vertical stripes, which can be 0.3 to 1 mm wide.
Treating the boxwood blight
Unfortunately, there is no complete protection against the boxwood leafdrop, because even the healthiest plants can be attacked in a humid environment. However, if you take care and keep your shrub neat and have a hardy variety in your garden, you can significantly reduce the risk of infection. A particularly susceptible variety is ‘Suffruticosa’. The ‘Herrenhausen’ variety, on the other hand, is more resistant and will have fewer problems with leafdrop in dry locations. If you want more information on the boxwood blight and how to combat it, simply click here.
The Volutella blight, also referred to as boxwood canker, can sometimes occur in massive outbreaks. The first and very obvious symptom of this illness are the tumour-like formations that grow on the shrub.
Causes and symptoms of Volutella blight
The cause of this disease is the Volutella buxi fungus, which can inflict enormous damage to the box tree. This fungus can penetrate into the shrub only through wounds, it then decomposes the bark as well as the wood of the box tree.
The Volutella blight is primarily recognizable by small growths at the entry points of the fungus, where the bark peels off. In addition, the shoots begin to wilt and dry over the infected areas. In most cases only individual shoots are affected and not the whole shrub. The wood around the affected area then turns greyish-brown to black and the leaves on these dead shoots turn light brown and hang on to them for a long time after they have dried up until they finally fall off.
If the weather is damp, a white fungi-like coating forms on the leaves and also on the shoots. This coating turns salmon pink when the fruiting bodies of the fungus form. Red globules sometimes appear on the branches and leaves, which are the fungus’s main fruiting form.
Treating Volutella blight
Unfortunately, all of the box tree varieties are susceptible to Volutella blight to the same degree. The infested box trees can be pruned back and the diseased parts can be removed. Since the blight is transmitted through wounds and injuries, it is also important to keep the tools clean. Preferably, they should be disinfected with 70% alcohol.
Not only the grain on the field can be attacked by rust fungi (Pucciniales), but also our beloved buxus is threatened by these. Especially the older specimens are plagued by the boxwood rust.
Causes and symptoms of boxwood rust
Boxwood rust is rather rare, but sometimes the symptoms of Puccinia buxi can be found on the leaves in spring. Rust fungi can be found on many different plants and are mostly yellowish to reddish in colour, but the small spots formed by the boxwood rust are rather brownish. These pustules are slightly arched, only about 2 mm in size and form on the top and bottom of the boxwood leaves.
Treating boxwood rust
To combat boxwood rust, it is sufficient to remove the affected shoots by pruning.
The box tree is also threatened and weakened by wilt fungi, including Phytophthora rot, also known as Phytophthora wilt. Especially wet soils promote the occurrence of this root disease.
Causes and symptoms of Phytophthora rot
For some time now we have been hearing reports from America, but also from the Netherlands, that the box is attacked and damaged by the fungus Phytophthora cinnamomoni or Phytophthora nicotinae. Phytophthora is better known as a disease in potatoes or other vegetables, but the evergreen shrubs can also suffer from this fungus.
These fungi prefer wet soils and attack the roots. They are characterised by withering, yellowing of the leaves and weakened growth. In the end, large parts of the box tree die off. The entire tree can succumb to this disease too. The buxus often looks as if it has dried out or frozen to death, but the cause is ‘only’ the fungus Phytophthora.
One can confuse the symptoms with those of the Volutella blight, but in the latter the wood of the box tree turns black or brown, which is not the case with Phytophthora rot.
Treating Phytophthora rot
Unfortunately, there is not much that can be done against this pathogen except to take preventive measures. Avoid waterlogging by drainage in any case and if you find infested plants, you should immediately remove them from your garden.
A brief summary of common box tree diseases:
- Boxwood blight (Cylindrocladium buxicola)
- Volutella blight (Volutella buxi)
- Boxwood rust (Puccinia buxi)
- Phytophthora rot
In addition to the diseases mentioned above, the box tree can unfortunately also be attacked by various pests. In this article you can learn which pests occur particularly often in box trees and how they can be controlled.
You can find out more about the box tree moth and its caterpillar and how to control it here.