Box Blight Cylindrocladium buxicola.
||What is Box Blight ?
Box Blight (Cylindrocladium buxicola) is a fungal disease
which specifically attacks plants of the genus Buxus (common name Box or
The original source of this fungus has not been satisfactorily determined,
originally it was suspected that regions in central America could be a possible source
however it has not been possible to substantiate this theory.
The fungus was first reported in the UK in the mid 90's and had become widespread
across Europe by 1998.
Studies by Beatrice Henricot (RHS plant pathologist specialist) and
Alastair Culham (Reading University) confirmed by sequencing of genomes and DNA
techniques that the fungus is a new species and it was named Cylindrocladium
It is an airborne fungus and the primary natural mechanism for the spread of
the spores is by water droplets borne in the wind, however as the spores are
sticky, then other means such as insects, birds, people and especially garden
shears/clippers are significant factors.
In common with other forms of Cylindrocladium 'resting spores' are
produced, these can remain viable for extended periods and are able to survive
drought and lack of host and may similarly be spread to other plants.
It is a 'cold fungus' and is unaffected by frost The fungus penetrates the leaf
directly via the stomata, which are holes through which the plant/leaf
breathes, and wounds or cuts in the leaf are not required.
Under favourable conditions the reproduction cycle is quite rapid
germination occuring some 5 hours after penetration, mycellium resurging and
conidia produced after approximately 48 hours.
The teleomorph (perithical) phase is not yet fully understood and
the implication is that the fungus reproduces by a heterothallic process. The
mycellium produced spreads from the leaf via the vascular tissues into the
plant stems where it clogs the plant's arteries restricting the functioning of
the Sap etc and ultimately causing death.
|Box blight in advanced stage
||Leaf detail in early stage of infection
IDENTIFICATION - What does Box Blight look like ?
Positive diagnosis is essential, leaf drop and plant death may occur for a
variety of reasons such as physiological damage, root death, scale insect or
cultural problems and hence any remedial treatment must be specific to the
Plantsprayers offer a free diagnosis service, for details click
The early stages of Box Blight infection are easily missed,
commonly it is not detected until parts of the plant die and pronounced leaf
fall occurs. Examination of the stems below the dead leaves will show dark
lesions in the vascular tissues, viewed through a microscope these lesions are
seen to be a mass of hyphae with conidium characterised by ellipsoid vesicle
with pointed apices.
The initial phase of infection in the leaf is indicated by a
general darkening often spreading in a circular fashion until the whole leaf is
discoloured, by then the fungus will have spread to the stem and the leaf
usually dies and turns a straw or tan colour. Unfortunately these colour
characteristics can be caused by a variety of other reasons making diagnosis
difficult to the untrained eye.
Frequently these leaves will be infected by secondary fungus,
Volutella, which creates a pink dusty mildew effect. Volutella itself is not a
serious problem, it is a wound pathogen which usually effects plants which are
suffering from another problem.
Box in gardens is frequently arranged in parterres, edging and knot
gardens etc and is clipped to regular forms and shapes. Advanced infections can
be readily recognised as often a central section of the top foliage will appear
to be dead whilst the side foliage retains its green. On a topiary piece, such
as balls, cones and spirals, commonly a small area comprised of individual
stems will die first, however the fungus will spread throughout the plant
eventually killing it
|Blight on Buxus 'John Browers'
||Blight on Buxus suffruticosa
TREATMENT - Can Box Blight be cured or prevented ?
Yes, Plantsprayers offer a spray treatment which is preventative
There are no effective fungicides available on the retail market
specifically for treating Box Blight.
PREVENTION - What cultural practices minimise the
risk of infection and spread ?
Box Blight, Cylindrocladium buxicola, is widespread
throughout the UK and as it is an airborne disease there is no guaranteed means
of prevention, however there are measures which significantly reduce the
possibility of severe infection.
The conditions in which the fungus proliferates are damp, shade and
poor ventilation, so avoidance of these will help prevent firm establishment of
It is most important to avoid overhead irrigation as the spores are
carried and activated in water droplets and damp leaves provide ideal
conditions for the fungus. Water the roots if required, possibly by a 'leaky
hose', Buxus do not need foliage irrigation.
Always ensure that all garden tools, particularly shears and
clippers, are clean. Do not infect healthy plants with dirty shears. Shears may
be cleaned by dipping in bleach or disenfectant mixed in the dilutions
indicated on the label for domestic/kitchen use.
Improving ventilation may be problematical, by its very nature Box
is often tightly clipped and hence poorly ventilated. With new plantings it is
worth bearing in mind ventilation and shade implications.
Removal of dead leaves, plant debris and foliage will reduce the
availability of spore releasing material and may reduce any 'resting spores'.
There are no Buxus species that are immune to Cylindrocladium
Practical experience however shows that some varieties seem more susceptible to
the disease, we suspect that this is not due to any inherent properties of the
plants but more due to the physical features such as water retaining foliage.
Typical examples are Buxus suffruticosa, B. Justin Brouwers, B.
Tide hill. All these varieties are commonly clipped and produce a plant with
small tight water retaining foliage thus producing an environment favourable
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