Brown leaves, a whitish coating on the undersides of the leaves and black stripes on the shoots - all these are signs of the boxwood fungus. Find out how to fight him here.
In German gardens and parks, boxwood plants have been threatened by the boxwood fungus for more than ten years. The aggressive pathogen Cylindrocladium buxicola is spreading from the north and is a big problem for boxwood owners. Because not only weakened or injured plants are affected. With prolonged moisture, the boxwood fungus succeeds in penetrating even he althy leaf tissue. Since the plants can also be attacked by other fungi, it is important to identify the pathogen responsible for boxwood dieback.
What are the signs of the boxwood fungus?
The boxwood fungus finds ideal conditions at temperatures around 25 degrees. The first signs of an infestation then become clear about seven days after initial contact. On the other hand, if the summer is particularly hot, the infestation will be limited, since the pathogen is much less able to cope with temperatures above 25 degrees.
The period for a possible infestation extends from April to August. First, there is discoloration of the leaves. The leaves then take on an orange-brown color on young plants. Older plants only turn brown. The leaf spots can spread quickly and entire shoots are infected. When the humidity is high, the undersides of the leaves are also covered by a whitish coating. However, the leaf spots alone are not a sure sign of the boxwood fungus.
Small black stripes that can be seen on the affected shoots provide a clear indication of the infestation. Initially, the drawing appears on the lower part of the shoot and spreads towards the top. As the disease progresses, entire shoots can be affected and die off. If the boxwood fungal infestation takes an unfavorable course, the entire plant will die.
For the layperson, it is often difficult to identify the boxwood fungus without a doubt. Various other types of fungus or an increased scale insect infestationrecognize a similar defect. The boxwood fungus is easily confused with the following diseases:
| Disease/Pest | Differences to boxwood fungus |
|---|---|
| Boxwood wilt | The bark shows extensive darkening. |
| Boxwood Crayfish | The spores are only initially white and later turn orange. |
| Box tree moth | Evidence of feeding damage is visible. The caterpillars of the box tree moth can be read. |
Fight boxwood fungus - how it works
It has not yet been possible to combat boxwood disease effectively because the fungus has proven to be extremely aggressive and resilient. If the pathogen has only penetrated through the he althy leaf tissue, there is no reliable method for combating it. Home remedies or biological substances fail. Chemical agents are also not permitted so far.
Recently, however, some users have had positive experiences with algae lime. If the plants were sprayed with algae lime in the spring, the boxwood recovered significantly over the next few months. The treatment is also said to be effective against the box tree moth and its eggs.
In the event of an infestation, immediate action is required. You should:
- remove all affected parts of the plant
- Prune the plant back to the he althy wood
- Dispose of all infected plant parts
- remove the fall foliage
- remove the top layer of soil
Important:
Infested plant parts must not be placed on the compost. The fungus would spread unhindered on the compost. The spores can survive on the ground for up to four years. To be on the safe side, you should dispose of the parts of the plant in the residual waste or burn them on the spot.
Due to the highly aggressive nature of the fungus, the tools used to cut back the boxwood, as well as the work shoes and gloves worn, must be thoroughly cleaned and disinfected after use.
How to prevent an infestation
➞ Select robust varieties:
Infestation with the boxwood fungus cannot be completely ruled out. When planting new plants, it is possible to switch to less susceptible varieties. These include Faulkner, Arborescens, Ilex Robustico® and Herrenhausen. The following varieties are particularly susceptible to infestation:
- Rocket
- Suffruticosa
- Blue Heinz
- Rotundifolia
➞ Select the correct location:
The leaves of the boxwood must be exposed to moisture for at least five hours before the fungus can penetrate the leaf tissue. This is avoided in a sunny and airy location as the leaves will dry off far more quickly. Incidentally, a calcareous, slightly moist soil is ideal for the boxwood.
➞ Customize the watering behavior:
The boxwood also needs sufficient moisture and nutrients. To avoid wetting the leaves unnecessarily, the plant is always watered from below.
➞ Protect the plant:
The fungus does not necessarily require injured leaf tissue, but will prefer to invade weakened growth. Therefore, pruning measures on the boxwood should be avoided during a humid and hot summer.
➞ Fertilize properly:
To strengthen the plants and thus make them more resistant to the boxwood fungus, potash fertilization in late summer is a good idea.