The dieback of boxwood can spoil entire gardens. A fungus is responsible for this. What can you do about the unsightly dieback?
The boxwood (Buxus sempervirens) can not only be found in artistically designed baroque gardens, but also in our own gardens. At Easter, even the branches of the box tree are consecrated in the Catholic Church, and in China the box tree is considered a symbol of long life. However, if the box is attacked by dieback (Cylindrocladium buxicola), its leaves and shoots will not have a long life ahead of them.
Boxwood dieback: causes and symptoms
In 2004, boxwood dieback was first detected in Germany and has been up to mischief ever since. The cause of leaf and shoot dieback in boxwood is a fungus, more precisely Cylindrocladium buxicola. Known as "box blight" in the UK since the mid-1990s, this fungal disease has been spreading ever since.
The first symptoms are individual brown, sometimes orange-colored spots on the box leaves, which continue to increase in size. The spots are darker in color towards the edge and flow together as the disease progresses. Black lines or streaks can be seen on the stems, and if you look closely (for example with a magnifying glass) you can see a white spore lawn on the underside of the leaf.
The box tree then sheds its leaves and the shoots become bare. Therefore, the dieback is also called "boxwood leaf fall".
Boxwood dieback: course and consequences
The prerequisite for infection is that the leaves are moist for at least five hours. The optimum temperature for this fungus is 25°C, but it stops growing at temperatures above 33°C and below 5°C.
When spores come into contact with the moist box leaves, they germinate after only three hours due to the moisture and grow directly into the plant tissue, wounds are not necessary for this. The infection of the plant can happen after 5 to 7 hours. After about a weekthen the symptoms appear and the leaves begin to fall off. As already mentioned, a white fungus lawn forms on the underside of the leaves. From there, the spores are spread by splashing water. The fungus Cylindrocladium buxicola survives on the fallen leaves in the soil by forming spores called chlamydospores. These spores can survive in soil for up to four years.
It is also possible that the boxwood carries the disease but does not show any symptoms. It is not yet known which environmental conditions are responsible for the disease breaking out after all.
Boxwood dieback: Measures against dieback
So what should you do to protect your beloved boxwood from dying instincts or, if it is already affected, to free it?
Boxwood dieback: take precautions
The prevention of fungal diseases starts with planting. Since the dieback needs moisture to break out, you should place your boxwood in a light and wind-free place so that it can dry off quickly.
Selecting the right plant can also prevent fungal infestation. Because there are also boxwood species that are less susceptible to dieback. These include, for example, Buxus sempervirens var. arborescens and the two Buxus microphylla cultivars'. Box varieties that are particularly susceptible are 'Blauer Heinz' and 'Suffruticosa'.
There are also a few things to consider when caring for your boxwood. If you water your box, it is best to water it close to the ground. Do not wet the entire boxwood with water, only the soil near the base of the trunk. Sprinkle the entire box, create optimal conditions for the dreaded fungus. When cutting the boxwood hedge, you should always pay attention to the weather. If you do not cut on warm, humid days, the injured leaves and shoots are particularly at risk of being infected by fungal spores. Boxwood hedges that are very dense and shaped are particularly difficult to dry and should therefore never be cut when it is damp.
Boxwood shoot dieback: Measures in case of infestation
An important point in combating shoot dieback is the removal of infested plants. If the drift dieback has spread in your garden, you must remove the diseased plants andremove the fallen leaves and either dispose of them in the residual waste, burn them, bury them deep or have them disposed of professionally. The pathogen is also in the soil, so you should also consider removing the top layer of soil. In addition, you should no longer plant boxwood in these infested areas. If you still don't want to do without a boxwood in the garden, you should try to propagate the he althy plants in your garden yourself so that the dieback doesn't spread again through purchased, possibly infested plants. Here you will also find beautiful alternatives to boxwood, which dieback cannot harm.
If you have handled infested plants, you should also thoroughly clean tools and clothing, preferably disinfect them. Otherwise you could spread the disease to he althy box trees yourself.
Boxwood dieback: Suitable sprays
Boxwood dieback can be combated or prevented with pesticides containing the active ingredient tebuconazole.
This active ingredient is found in many products, such as Baymat Pilzfrei. The optimal application period is from April to October. The agent has a systemic effect against many different fungi on roses and ornamental plants. This means that the active ingredient is absorbed after spraying and then spreads throughout the plant. However, this remedy should not be used on boxwood more than six times a year, with an interval of at least one week between applications.
The Curamat rose-fungus-free product can also be used against boxwood dieback. It also contains the active ingredient tebuconazole and it is injected. Here, too, the maximum application is six times a year and the spraying interval is at least seven days. It should be used at the onset of infestation or when the first symptoms become visible.
Unfortunately, the use of tebuconazole can be harmful to some beneficial insects, such as predatory mites, curlews, ladybirds or parasitic wasps. If you've introduced these beneficial insects to your garden to control other pests, you should reconsider using one of these fungicides.
Boxwood dieback: possibility of confusion
The Volutella branch dieback caused by Volutella buxi can easily be treated with thebe confused with drive deaths. The leaves dry up, get a pale green color and a pink spore lawn forms on the underside. A clear distinguishing feature, however, are the . These stripes only appear during dieback, but not with Volutella.