Ideally, the evergreen boxwood has its beautiful, green foliage all year round. However, if it turns brown and dries up, the plant should be examined more closely. Because it is not uncommon for these to be symptoms of a fungal disease or pest infestation. We will explain to you how you can identify the cause of the brown discoloration and subsequently combat it.
Fungal diseases
If the leaves suddenly turn brown and dry out, this can often be attributed to a fungal disease. However, which fungus is causing the symptoms can usually only be determined upon closer inspection. In principle, however, the following applies: As soon as a fungal disease is suspected, action should be taken immediately!
Shoot death / boxwood fungus
The dreaded shoot death is caused by an ascomycete called Cylindrocladium buxicola. The fungus is favored by warm, humid weather and is blown onto the shoots and leaves by the wind. An illness is initially noticeable in the presence of many small white-greyish spore deposits. As a result, orange to brown spots appear on the top of the leaf, which become larger and larger and ultimately grow together to form a large area. If the fungus is not controlled, the fungus will continue to spread. The leaves fall off and the shoots gradually die. It is therefore advisable to act immediately if symptoms appear:
- Cut back the boxwood immediately and vigorously
- Pruning down to the he althy tissue
- dispose of cut shoots in household waste
- rake up fallen leaves and dispose of them
- remove the top layer of soil
Note:
It is advisable to remove the top layer of soil as the fungus can easily survive in the soil for several years.
Boxwood wilt
Boxwood wilt can be traced back to the ascomycete Fusarium buxicola, which primarily attacks old boxwoods. A disease is first noticeable in the leaves, as they become wilted and leathery. In addition, dark brown spore deposits can be seen on the leaves, usually as small dots. If the fungus continues to spread unhindered, it can also attack the shoots. However, the shoots are usually only affected relatively late. If the plant suffers from boxwood wilt, it is best to proceed as with the boxwood fungus:
- strong pruning down to the he althy tissue
- dispose of fallen and cut leaves in household waste
- remove the top layer of soil
Boxwood cancer
Boxwood canker occurs mainly in weakened plants. However, it can also be caused by care errors. Because drought stress and waterlogging as well as a lack of nutrients and an incorrect pH value promote the occurrence of boxwood cancer. If the plant suffers from boxwood cancer, this is initially noticeable in twisted and clinging leaves. The foliage initially turns yellow, then brown and finally falls off. Pink pustules may also appear on the leaves. If the boxwood canker is not treated, the tree will tear open or even detach itself from the wood. Whole branches can also dry out. Here too, it is advisable to act quickly:
- Cut back boxwood vigorously
- down to the he althy tissue
- dispose of diseased plant parts
- also the fallen leaves!
Boxwood rust
Another dangerous fungus for boxwood is the rust fungus Puccinia buxi. This mainly affects older and weakened boxwood trees and settles on their leaves in spring. The fungus penetrates further into the tissue, so that rusty brown spore deposits become noticeable on the leaves in autumn. Boxwood rust should also be combated immediately:
- cut off infected shoots
- dispose of in household waste
- use fungicide if the infestation is severe
Pests
Brown and dry leaves are not always a sign of fungal diseases, as the symptoms can also occur in the event of a pest infestation. However, the unwanted pests can usually be combated relatively easily and, above all, successfully.
Box tree spider mite
The boxwood spider mite prefers a dry and warm climate, which is why infestations usually occur in summer. This can initially be recognized by fine, yellowish stripes and spots on the leaves. The foliage subsequently turns bronze to brown and dries up. If the infestation is not combated, leaves will eventually fall off. However, boxwood spider mites can usually be effectively combated as follows:
- Use oil-based agents
- this will destroy the eggs
- Spider mite remedies in spring
- natural enemies: predatory mites
Box tree gall midge
An infestation with the boxwood gall midge causes approximately the same symptoms as with an infestation with the boxwood spider mite. The resulting spots are also yellowish, but larger and less sharp. In addition, the underside of the leaf is bloated like a bubble. If only individual leaves are affected, this is usually not a cause for concern. However, the situation is different if the infestation expands. This can lead to massive loss of leaves and thus weakening of the plant. In the event of an infestation with the box tree gall midge, it is best to proceed as follows:
- remove individual leaves in spring
- before the larvae hatch
- prune boxwood in case of severe infestation
Note:
The larvae of the box tree gall midge are a welcome meal for many songbirds. Tits in particular are attracted by them and could cause additional damage to the box tree.
Harmless causes
Brown and dry leaves are not always a cause for concern. Because it is not uncommon for these to be natural reactions of the plant or care errors. Intervention is not always necessary in these cases, as the brown leaves usually turn green again on their own.
Too little water
Adequate water supply is one of the basic requirements for he althy growth of the boxwood. However, if the plant is in a particularly bright location and it has grown too densely, water absorption can be impaired. Because in this case the rain can not only reach the dense foliage into the ground. The boxwood therefore does not absorb enough water, which in turn causes the leaves to turn brown. However, this can usually be remedied with the right watering behavior:
- water regularly
- even in the rain!
- Special fertilizers in spring and summer
- this strengthens the boxwood
Sunburn
It is not uncommon for entire areas of the bush in the same direction to turn brown. The south to southeast side is mostly affected. If no other symptoms occur, this can usually be attributed to sunburn. Especially when the leaves are covered with hoarfrost and suddenly get a lot of sun.
Cold
If the boxwood gets yellowish or brownish leaves in winter, this is usually not a cause for concern. This is a natural reaction of the plant, which wants to protect itself from the low temperatures. In this case there is nothing to do because the leaves will turn green again on their own.
