For many years the boxwood was considered a robust shrub that was hardly affected by any disease. The box tree, which originally comes from regions with an oceanic climate, has not had to fear any diseases or pests in Central Europe for a long time. In recent years it is not only the boxwood moth as a pest that has troubled the bushes, but also various fungal infections.
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In the case of boxwood diseases, shoot death is now the top priority. The boxwood fungus (Cylindrocladium buxicola), which was even named after the box because it only attacks these shrubs, is responsible for the death of shoots. The fungus mainly penetrates the leaves and gradually kills the entire plant. The fungus itself is insensitive to frost and can even remain inactive in the soil for several years until the weather conditions are suitable for an infestation.
The ideal time for an infestation are humid and warm summer months. Rain and splash water are not only responsible for the transmission, but also form a breeding ground for the leaves. Therefore, box trees that were planted as a hedge along roads are mainly endangered. The leaf surface must be continuously moist for at least five hours so that the fungus can penetrate the leaf. In particularly favorable weather conditions, the mushroom can even do it in three hours.
There is an increased potential for contagion under the following conditions:
- very young age of the boxwood
- Open cuts after cutting back or due to injuries
- increased and prolonged humidity due to the weather
- Weakened by stress such as periods of drought
- Weakening of the wax layer on the leaves
Boxwood diseases are often recognized very late and, especially when the shoots die, only a few leaves are affected at the beginning. This should be checked, however, because on the underside of infected leaves there is a white to gray coating of spores. In the further course, orange-brown to dark brown spots form on the upper side of the leaves in the direction of the petiole. The entire leaf is affected within a short time and the upper side also gets a gray tinge. Eventually, necroses form in the shoots and they finally die.
Confusion with other types of damage
Recognizing boxwood diseases is usually not very easy, as many fungal diseases have a similar course and, at first glance, a similar damage pattern. In comparison to other diseases, the death of the shoots can be recognized by the fact that the spore coating is gray at the beginning and later turns orange to brown. In the case of boxwood withered, for example, the bark would also be infested and significantly darker.
Preventing the death of shoots
When buying the shrubs, care should be taken to ensure that the plants are healthy and strong. A good supply of water and nutrients promotes a good overall condition. It is always poured close to the ground, which means that the leaves do not get wet and fungal spores do not find a breeding ground. If the boxwood is cut, a dry period should be chosen if possible. If there is a risk of infestation due to prolonged weather conditions with a humid and warm climate, the shrubs can be treated preventively with a fungicide. Preparations with tebucunazole have proven to be effective.
There are some fungicides that are used successfully against shoot dieback. They have the advantage that, when used according to the instructions, they do not pose any health risks and are also harmless to insects such as bees. The following fungicides have proven themselves in practice and show a good preventive effect:
- Rose-mushroom-free Ortiva (no incompatibilities with other plant species and can be used for other fungal diseases)
- Duaxo Universal mushroom-free (can also be used as a universal fungicide for ornamental plants, fruit and vegetables)
- Mushroom-free Ectivo (suitable for ornamental plants and fruits)
Fight boxwood fungus
The following options are available to combat the boxwood fungus:
- Cut out the affected areas generously
- Dispose of cut and fallen parts in the residual waste to avoid re-infection
- Remove the top layer of soil and also dispose of it in the residual waste
- Treatment with a systemic fungicide
In the case of boxwood cancer, it is again a fungal disease. In this case, the “Volutella buxi” fungus is responsible. Recognizing boxwood shrimp is not that easy, as in this case, as in the case of shoot death, entire shoots die off. Compared to boxwood shoot death, however, the plant remains largely healthy, even if entire shoots are infected.
Requirements for boxwood cancer
Especially at risk are bushes that are in the shade, which means that they cannot dry the leaves so quickly after a rain. In addition, cuts encourage the fungus to penetrate, especially when there are extreme weather conditions with a warm, humid climate. Infestation is also favored if the plants are weakened by poor care. The fungus is mainly spread via the foliage.
Boxwood diseases caused by fungal attack are easy to control, but not always easy to recognize. Compared to the shoot death, the leaves do not change color directly, but simply lose their shine and turn pale green. The spore coverings on the underside are pale pink, which in turn allows the infestation to be differentiated from the shoot deaths.
With an advanced infection, typical cancerous wounds appear. The bark will then begin to peel open and peel off.
Gardeners can prevent boxwood cancer by being careful not to cut at an inconvenient time, especially when it comes to bushes in shady locations. In addition, these measures help to control or prevent boxwood cancer:
- adequate supply of the bushes with nutrients
- Regular control of the pH value and, if necessary, adjustment through soil improvement measures
- Cut out affected parts of the plant generously
- Plant parts and fallen leaves are not composted, but disposed of in the residual waste
Treatment with a fungicide is usually not necessary. The boxwood shrimp can usually be got under control by pruning hard.
The tree rust, which can attack different trees and bushes, is also one of the boxwood diseases. As with other boxwood diseases, it is again a fungal infection this time caused by Puccinia buxi. Boxwood rust is easy to spot, but difficult to control.
The boxwood rust almost exclusively affects old bushes. Especially when they develop poorly because of a lack of nutrients, for example, they offer the fungus a target to attack. An illness is in turn favored by warm, humid weather.
Boxwood rust can be distinguished from other fungal infections in that brown bumps that look like rust spots form on the upper side of the leaf. White spots form on the underside of the leaf, which at first confuses it with shoot death. However, the brown discolored areas differ from the shoot deaths by an elevation.
Gardeners can only prevent tree rust to a limited extent, as the age of the bushes plays a major role. Regular pruning and thus continuous rejuvenation of the plants can prevent this to a limited extent. Boxwood rust is also stubborn and difficult to control. Affected branches have to be shortened considerably, which often also weakens the shrub itself, as you have to cut deep into the old wood. The box must then be treated with a fungicide. Preparations based on copper, for example, are suitable for combating tree rust. Cut off plant parts should again be disposed of and not end up in the compost.
Boxwood diseases can be persistent and, if identified too late, destroy the entire shrub. While boxwood cancer and rust can be combated well, shoot death is a major problem due to its many possibilities of infection. Endangered shrubs along busy roads, for example, should be treated preventively with a fungicide.