Further Information about Box Hedging
Pests, Diseases and problems of Box hedges.
Box blight is usually caused by Cylindrocladium buxicola or Pseudonectria buxi, both fungal infections making the leaves turn brown or grey/pink or bronze and causing dieback of the Buxus stems, in ideal conditions of warmth and moisture hedges and topiary specimens can spread quickly. Fortunatly there are many practical measures that can be implemented
- Do choose a dry breezy day in early summer to trim your Box hedge plants and topiary, the cut edges will dry much more quickly, greatly reducing the chance of spores entering your plants
- Do trim just once a year, the less you trim the smaller chance of infection and a slightly ‘looser’ hedge will have better ventilation.
- Do use hand shears, they will make a neater job than a hedge trimmer with far fewer cut edges.
- Do trim back hard enough, the centre of a Box hedge that gets wider and wider each year will not dry so quickly and therefore will be more likely to harbour an outbreak.
- Do disinfect shears or other pruning tools as you progress with Jeyes fluid or dilute bleach
- Do consider a ‘before and after’ fungicide spray at trimming time. If you garden an area with a high incidence of blight then a belt and braces approach may be the way forward. Bayer have two approved products (Bayer fungus fighter and Bayer fungus fighter plus, both containing the active ingredient Tebuconazole) that could be used before and after trimming following the label directions.
- Don’t trim too late in the season, any re growth needs time to ripen fully otherwise it will be vulnerable to frost damage that will allow fungal spores entry into your plants.
- Don’t water your Box hedge plants if you can avoid it, if you must then always water from below so that the foliage stays dry.
- Don’t put all your eggs in one basket. Don’t plant Box topiary next to a box hedge…. use Yew or Bay topiary instead, or plant a Yew hedge (yes you can keep it that small!) and have box topiary, in short don’t plant Box, Box and more Box – mix it up a bit by making your garden more species rich and so manage the risk. An outbreak of blight in these circumstances would be a matter of sadness instead of tragedy.
- Do experiment with other shapes of hedge, a palisade or wavy topped hedge has a bigger surface area and will dry faster, even a convex top is better than a square one. Experiment with cutting some circular ‘windows’ into your hedge to improve airflow or even a hedge with regular small gaps that would act like a ‘fungal firebreak’.
- Don’t use a high nitrogen fertiliser on your box, excessive soft leafy growth will always favour blight, use a more balanced feed instead with extra magnesium for a rich deep colour without extra growth, seaweed fertiliser is ideal, use in moderation.
- Do use a (shallow) mulch around your box plants, they have fleshy roots that like to stay close to the surface and will appreciate the moisture while the mulch will go a long way to reducing rain splash.
- Do enforce a trowels length exclusion zone around your Box hedges – keep border plants chopped back so that air can circulate right down to the base of your Box plants keeping the leaf surfaces as dry as possible.
- Do buy new Box hedge plants from a reputable supplier with a plant passport number, these nurseries are inspected annually by the Plant Health & Seeds Inspectorate. While they are not inspected specifically for box blight it is without doubt a nod to good practice and management. A specialist hedging plant nursery that grows its own stock (rather than a trading nursery or garden centre) will have a disciplined approach to the cultural control of box blight
- Do consider planting a variety with some resistance, Buxus microphylla ‘Faulkner’ has at least some resistance to blight and makes a lovely hedge or topiary subject of similar proportions to Common Box with slightly more rounded leaves of brighter green.
- Do design new gardens with Box hedges to have plenty of airflow, make the path a little wider, have grass or decorative stones or paving between the Box hedges instead of wall to wall planting.
- Do exercise the strictest gardening hygiene around your box plants, cleaning up fallen leaves and clippings, a ‘garden vac’ is worth its weight in gold for larger areas.
- Don’t compost your box trimmings or leaves, they are a potential source of inoculum and the spores can remain viable for up to 6 years. Burn it or bin it!
- Do observe your Box hedges regularly, early diagnosis can massively reduce the impact of an infection because remedial action can be taken quickly before the disease gets a real hold.
- Don’t plant Box hedges in dark or damp corners of the garden as this really is asking for trouble! Choose a different, more suitable species of low growing hedge.
Practical ways of dealing with Box blight
If you are unfortunate enough to have blight in your garden, above all else, act quickly. The sooner you remove and destroy infected plant material the quicker the outbreak will be brought under control and permanent damage to your Box will be minimised.
Before you grab a spade in anticipation of digging them all up and burning the lot – there are other options, (and yes they are effective) listed here in order of severity:
- Localised removal of infected wood, recommended where the disease has been caught in its very early stages it is often possible to cut out a little more than may appear necessary in conjunction with a fungicide application both before and after. Especially suitable for topiary specimens and hedges with a minor infection. Choose a dry day and remove all infected leaves and stems after they have been pruned out.
- Hard pruning to remove infected parts, if you catch the disease reasonably early it may well be possible to reduce your hedges by 50% or more on a dry day, being sure to remove every scrap of the trimmings and fallen leaves to the bin or bonfire. It pays to cut back further than you think, the infection can be latent in apparently healthy wood so be brave, they will grow back!
The photos show a series of Box hedges reduced in width from 60cm to just 20cm, seemingly brutal treatment but If timely and decisive action is taken (and the hedge is in otherwise good health) then re growth can be surprisingly quick, young shoots can emerge from even the most unpromising woody stems within a matter of weeks. Best practice would also involve removing a shallow layer of topsoil from immediately around the base of the hedge as this will no doubt be laden with fungal spores. Replace with a shallow mulch and give the hedge a moderate feed to encourage re growth.
- Pruning back to stumps, a more drastic approach if blight has really got a hold. Although blight wreaks havoc with the leaves and stems, it doesn’t kill the roots. The advice above still applies, bin or burn everything you chop off and choose a dry day. Cutting back to stumps of 5 or 10cm allows for an almost clinical post-operative clean-up of infected leaves and removal of infected soil followed by mulch and feed. Re growth will often be much faster than you might expect and probably quicker than re planting as the established root network is still in situ.
- Monitor new growth, having already carried out a thorough removal of all sources of infection, the chances are that the new green shoots will be healthy and free of blight and by following our tips for avoiding blight they should stay that way. There is no reason why a hedge should not recover completely with some sympathetic treatment and maintaining good airflow.
- Complete removal and replacement, if you have tried various degrees of surgery on your Box hedges and done everything possible to aid its recovery, only to see its new shoots become re infected – then it may be time to admit a gracious defeat.
Sometimes no amount of hard work can overcome local environmental conditions that seem to favour the blight much more than the box. Some gardeners prefer to deal with certainties from the outset and would rather commit to replacement over rejuvenation at the first sign of infection.
Box Tree Caterpillar
The most recent unwelcome visitor causing problems in our box hedges is the Box tree caterpillar Cydalima perspectalis. First reported on our shores in its adult moth stage in 2008, the devastating caterpillars were not discovered in private gardens until 2011 but they have since become more widespread in and around London.
The adults lay their eggs on the underside of leaves on Box hedges, the striped green and black caterpillars that hatch defoliate the host before covering it in the same silky webbing used to form its cocoon. Three or four generations of this voracious new pest are possible in a long warm summer. Affected Box plants are often severely defoliated, the leaves are devoured almost in their entirety leaving little more than a network of green stems and leaf ‘skeletons’ behind. The remaining leaf parts will die and an untreated outbreak will weaken a Box hedge making it more susceptible to other pests and diseases.
The adult moth usually has white wings with a slightly iridescent brown border although the wings can be completely brown, or clear. The pest appears to overwinter as small caterpillars hidden in between box leaves that have been woven together with its distinctive silky webbing, the caterpillars complete their development the following spring completing a new generation.
Practical ways to deal with Box Tree Caterpillar
These stripy imposters are never likely to be welcome in any keen gardener’s plot but they are thankfully somewhat easier to deal with than box blight – which is a good thing as they are becoming more common with each passing year according to the responses to the RHS box tree moth survey. (On a side note – At home I am a great believer in letting our brood of (very free range) chickens have full garden access on special occasions, they do a sterling job with slugs, snails and vine weevils leaving no fallen leaf unturned I am confident they would seek out deal with Box caterpillars too)
- Remove the caterpillars by hand, with a little patience (and manual dexterity!)
- Use a biological control, although this approach may take time as the predatory parasites will need to multiply and will only be effective in warmer temperatures. The nature of a biological control will need the pests to remain, albeit at acceptably low numbers to sustain the predators.
- Pheremone traps – these can be very effective and a specific impregnated lure for the box tree moth is available from Agralan ltd.
- Chemical control – by spraying with a suitable insecticide such as Bug Clear (pyrethrum) or Bayer Provado Ultimate Fruit & Vegetable Bug Killer (deltamethrin). Because of the persistent nature of the silky webbing surrounding the caterpillars as they feed, attention is needed to achieve effective spray penetration. (Special care should be exercised when applying insecticides to avoid plants with open flowers so that bees and other pollinating insects are not harmed).
Once an outbreak is brought under control monitoring is advised to determine if the caterpillars have returned and if so, further measures should be undertaken.