Box Blight Cylindrocladium buxicola.

IDENTIFICATION

TREATMENT

What is Box Blight ?

Box Blight (Cylindrocladium buxicola) is a fungal disease which specifically attacks plants of the genus Buxus (common name Box or Boxwood).

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 buxicola.

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 problem.

Plantsprayers offer a free diagnosis service, for details click here.

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 and curative.

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 the disease.

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'.

IMMUNITY, RESISTANCE

There are no Buxus species that are immune to Cylindrocladium buxicola.

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 for fungus.

BACK TO TOP OF PAGE