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Fungal diseases

 Dansk

Box blight (Cylindrocladium buxicola)

"Why does my boxwood wilt?"

Cylindrocladium buxicola
Heavy attack in an old garden. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
Here you can't save the hedges. You have to plant a nev variety. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
Light or dark brown leaves are the first signs of infestation by Cylindrocladium buxicola. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Names

Buksbomkvistdød (Danish)

Box blight

The Cylindrocladium fungus is especially known by people who work with Rhododendron and Azalea, but it also attacks other woody plants. Here, however, we are talking about the species Cylindrocladium scoparium. This species is a known pathogen, also related to various potted plants in which it attacks both leaves, stems and the roots of them.


Box blight is currently used for numerous purposes in the Danish gardens and parks. It is loved for its many qualities. Evergreen plant to stern, solitary or cut into countless shapes it is quite indispensable. The plants in this genus are slow growing, making them especially suitable for small gardens. Boxwood is hardy and can grow in both sun and shade. .
Therefore, you become a little nervous when a new plant disease threatens to destroy boxwood. The increase in trade with the rest of Europe, especially when it comes to plants, Germany and Holland, have also been the cause for plant diseases beeing carried around. Cylindrocladium buxifolia is an example of this.

This is a very serious disease, but with some simple measures and a degree of forethought it can hopefully be avoided.
The fungal disease is relatively new in Denmark. In England it was registered and described around 1995. Later it spread to Germany and Holland where especially in the summer of 2004 and 2005 there were quite a few attacks. Here in the year 2010, one must assume that it exists in most parts of Europe and now also in Denmark, where for the past 2-3 years we have registered widespread attacks

Cylindrocladium buxicola
The attack often begins with a round, circular spots with a brighter spot in the middle. (Cylindrocladium buxicola ).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
Longitudinal brown streaks on the stems is a typical symptom of the attack. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Symptoms

The first symptoms are often seen on the leaves. Dark brown, occasionally light brown spots. In the beginning, they are circle-shaped often with a light brown/orange center. Quite rapidly the fungus spreads and the entire leaf is stained dark brown. The stems are also attacked, and here you will see longitudinal brown stripes. The fungus Also attacks the root system and you will discover damping-off-like symptoms.
Box blight may in certain circumstances be confused with another fungal disease of boxwood, (Volutella buxi). You can quite easily even make the correct diagnosis. Cut off branches with infested leaves and put them in a plastic bag with some moist paper towel. Then place the plastic bag in a room at about 20 ° C. for 2-3 days. In these humid conditions the Cylindricladium develops a white to grayish fur on the underside of the leaves. With a strong magnifying glass (15 x magnification), it is in fact possible to see the rod-shaped spores which is up to 80 microns in length. (There are 1000 microns in a mm). Volutelle, unlike Cylindrocladiumen has a light pink to apricot-colored fungal coating.
By severe attacks the leaves fall gradually by. In the case of older plants such as the boxwood hedges, one can observe that the top is often green, while the rest of the hedge has wilthered. Plants without leaves dies.

Cylindrocladium develops rod-shaped vegetative spores on the underside of the leaf. It also forms mikrosklerotier, thick-walled cell structures in the leaves that presumably can survive for several years in the upper soil layers. However, there is great uncertainty about how important this source of infection is. We are indeed talking abou a serious disease in boxwood. Especially when parts of the old established hedges dies.

Cylindrocladium buxicola
Under humid condition the mycelium and spores (conidia) develops on the underside of the leafs. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.




Cylindrocladium buxicola
Here you can see the underside of a leaf from the leaf edge to the center through a microscope.
One can discern the rod-shaped spores. (Cylindrocladium buxicola ).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
In the microscope the rod-shaped spores are clearly visible and not to be mistaken. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
Conidia are tocellede and measuring in length about 60-80 my. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
In the leafs there are formed mikrosklerotier wich are a thick-walled, resistant cell structures (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
The different structures are developed in connection with sporulation of Cylindrocladium buxicola. (Cylindrocladium buxicola).
Foto: Magnus Gammelgaard.


Cylindrocladium buxicola
The dark brown growth on artificial medium (PDA), is typical of Cylindrocladium. Here a 6 day old culture..
(Cylindrocladium buxicola)
.
Foto: Magnus Gammelgaard.


Risk of confusion

another fungal disease, boxwood twigblight(Volutella buxi), are fairly common. This fungus results in pale yellow leaves and withered shoots and plants and is most common in springtime. The fungus forms a second type of spores. Here, there is pink to skin-colored spore pads on the underside of the leaf.

Progress of disease

The Fungal disease attacks especially in late summer or autumn. It is to be considered a "cold-fungus", in contrast to other fungi developing well under cool conditions. Even at 5 degrees C the fungus can grow. Optimum temperature for fungusgrowth is 25 degrees C, but at 30 degrees it goes to a halt. The fungus is humid-loving. When the spores lands on the leaves it is required that the leaves are moistened five to seven hours at a time to enable them to grow. It is not required as for many other fungal diseases, that the leaves are wounded, so that it may penetrate into the leaf. When it is inside the leaf the mycelium spreads to the entire plant through the vascular bundles.
Fungus spores developes under humid conditions and can be spread by wind. However, there is no question of spreading over large distances as we know it for many other fungi. The spores are sticky and can therefore be carried around by insects. Heavy rain and "rain splash" can spread the spores to neighboring plants. Handling of plants, including hedge trimming is also an important spreading factor. Purchase of infected plants are often the beginning of an attack.

There is a difference in boxwood species susceptibility to this fungal disease. German studies indicate that the varieties: B. sempervirens 'Suffruticosa', B. P. 'Rotundifolia', B. P. 'Handworthientis' B. P. 'Rocket' and B. p 'Ingrid' is considered to be very receptive.
B. p 'Arborescens', B. P. 'Elegantissima' and B. p 'Aureovariagata' is reported to be moderately susceptible, while B. microphylla 'Faulkner' and B. m 'Herrenhausen' characterized as weakly susceptible.

Frank Kirkegaard mentions in his article on boxwood in the 'Haven' No. 1 2012 the variety 'Blauer Heinz as a good alternative and describes the variety as "Compact growing and healthy blue-green variety that can be used as a low hedgerow instead of 'Suffruticosa."

This disease is a decidedly "hygiene disease." Firstly it is important to avoid acquiring diseased plants. Here one could assume that the Danish-produced are the most healthy. If you have the disease in your garden your pots, scissors knives and other paraphernalia used in handling, has to be disinfected in a fungicide bath. For example Rodalon

Countermeasures

  • Check the newly purchased plants fot symptoms: Affected plants are discarded.
  • Hygiene is important: all the paraphernalia, including knives, scissors, pots, boxes, clothing, etc.. that have been in contact with diseased plants should be disinfected. For example, use Rodalon.
  • Plant location should not be under shady conditions.: Fungal disease develops mainly on plants standing in the shade and on wet leaves.
  • Cutting in dry weather: Hedge Clipping of moist plants involves a significant risk of contagion.
  • Not spraying: When growing boxwood you should avoid leaf wetness and watering from above. In particular, if you do it at the end of the day.
  • Resistant varieties: Obtain if possible resistant varieties.
  • Healthy cuttings: Take cuttings only from healthy plant material and preferably only in the top of the plants.


Plant instead

boxwood is not easy to replace. In "Grønt Miljø" nr. 7, september 2011 Japanese holly (Aquifoliacae) is suggested. (Ilex crenata 'Dark Green') It resembles boxwood and can grow in the same places. Another possibility is Taxus. The same magazine discusses a clone of Buxus sempervirens 'Arborescens' from E. Lund Andersen's Nursery, which originally comes from Sweden by Professor Georg Georgsen and are planted at Soro Academy as being resistant. This is not verified.

Control

  • Remove infested shoots and leaves: Cut off infested shoots as soon as they show symptoms. If the disease has already spread dig up the plant and disposed it. Dead leaves should if possible be removed as they may be source of infection in the upcoming growing season.
  • Replace the soil: when planting, the soil should be replaced as there may be infested roots. Similarly, there are mikrosklerotier (resting spores) in the topsoil that has to be removed .

Chemical control

There are no approved pesticide for the control of Cylindrocladium buxicola. Chemical control is not a viable option when it comes to private horticulture. The industry has certain fungicides used to control other fungal diseases, and it has a side effect on this fungus

Articles in danish

http://www.gartneriraadgivningen.dk (artikel i garnertidedende nr. 16 2010 side 35 af Bent Leonhard)/


Opdateret d. 7.11.2014

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