My box hedge has brown patches. Is it box blight, and what do I actually do now?

Q. My box hedge has developed straw-coloured patches and the leaves are dropping. How do I know whether it is box blight, the box tree caterpillar, or something else entirely?

A. They look different if you know what to look for. Box blight, which is caused by the fungus Calonectria pseudonaviculata (also listed in older references as Cylindrocladium buxicola), turns the leaves brown and they fall off, leaving bare stems with no obvious insect damage. In humid conditions you will sometimes see white, powdery spore masses on the undersides of affected leaves just before they drop, and the young stems develop dark, irregular streaks rather than clean green shoots. Box tree caterpillar is a completely different problem, caused by the larva of an Asian moth that first reached Britain in 2007 and has been found in gardens around London and the home counties since 2011. Look inside the hedge for webbing and for green-and-yellow caterpillars with a black head; the leaves are eaten rather than turning brown and falling. You can have both at once, which is not unusual on established box hedges. Drought stress produces a similar straw colour but the patches usually follow the most exposed or shallowest-rooted sections, not a random spreading pattern. If the browning is following the clipping lines on the outer surface, that is often physical damage from cutting in hot sun, not disease. The RHS has an illustrated guide to box blight identification worth looking at before you draw any conclusions, and our box hedge care service includes a diagnosis visit if you want a second opinion in person.

Q. Box blight seems to be everywhere in my part of Rochester. Why is it so bad?

A. Sheltered, walled gardens are exactly the conditions that blight thrives in. Calonectria pseudonaviculata spreads very rapidly in warm, humid air, and a dense formal box hedge against a south-facing wall, with very little airflow between the plant and the boundary, is almost a petri dish for it. The fungus was first recognised in the UK in the mid 1990s and has been spreading through formal gardens ever since. It is not a sign the hedge was badly maintained. It is a sign the conditions were good for the hedge and, as it turns out, equally good for the fungus. Mild, damp spells in late summer and autumn suit it particularly well.

Q. About a third of my hedge is bare patches now. Is it worth trying to treat it, or should I cut my losses?

A. At roughly a third affected it is genuinely on the borderline, and the honest answer depends on whether the patches are stable or still spreading. If the bare areas appeared last winter and have not significantly grown since spring, there is a reasonable case for trying to cut out the infected sections and manage the rest. If the patches have been actively expanding through the current growing season, the fungus is still active, and at that stage arrest is genuinely difficult. For what it is worth, the RHS recommends against using fungicides on box blight: they are unlikely to be effective once the disease is established, and the fungus can survive on fallen leaves and debris for years. The practical options are aggressive pruning of affected material followed by strict hygiene discipline, or replacement. We would give you a straight assessment on site rather than a speculative answer from a photo, but our rule of thumb is that if more than half the hedge is bare and the patches have been spreading for more than one full growing season, replacement is almost always more cost-effective than the ongoing management effort.

Q. If I do try to save it rather than replace, what is the right way to manage it?

A. The two non-negotiables are timing and hygiene. Cut out all visibly infected material during a dry spell, not in wet or humid conditions: the spores spread on water droplets, and cutting a blighted hedge after rain is one of the fastest ways to distribute the disease into clean sections. Every clipping goes into a bag and straight into the general waste bin, never the compost heap. Sterilise your shears or hedge trimmer blades between passes along the hedge, and ideally between individual plants if yours is a hedge of separate rooted stems rather than a continuous root system. Beyond that, allow more airflow than you usually would: do not clip the surface as tightly as you might otherwise, because a slightly open canopy dries faster after rain and gives the spores fewer opportunities to establish. On ongoing annual maintenance cuts, avoid cutting in wet weather and avoid cutting immediately before a forecast wet period. That is roughly what we do on the box hedges we maintain regularly, and it keeps the disease from worsening rather than eliminating it entirely.

Q. My hedge is in the Rochester Conservation Area and the stems look quite mature. Does that affect what I can do if I want to remove and replace it?

A. It may do. Under section 211 of the Town and Country Planning Act 1990, work on a tree (including a hedge plant that has grown to tree size) with a stem exceeding 75mm in diameter at 1.5 metres above ground level in a Conservation Area needs six weeks' written notice to Medway Council before the work starts. Medway is the administering unitary authority here, not Kent County Council. Most box hedges, even mature formal ones, have individual stems below that threshold, but if yours has been in place for many decades and forms part of a knot garden or formal parterre, some of the principal stems may be over 75mm. The notice period is not a planning consent: you submit the notification, wait six weeks, and unless Medway makes a Tree Preservation Order in the meantime, the work can go ahead. Failing to give notice carries a fine of up to £20,000 in the magistrates' court under section 210 of the Act. Our Conservation Area Q&A has the full detail on the notice procedure and what to include. If you are in the Conservation Area and you want us to assess the stems before you decide, we will do that as part of the site visit at no extra charge.

Q. If we do replace it, what is the best alternative for a formal hedge in a Rochester garden?

A. For a close visual match to box, Ilex crenata (Japanese holly) is the most widely recommended alternative and the one I would look at first. It has small, dark, glossy leaves that clip to a tight formal surface very similar to Buxus sempervirens, it is fully evergreen, and it has no susceptibility to either box blight or box tree caterpillar. The main caveat is that it establishes more slowly than box: expect two to three growing seasons before it reaches a clipped density comparable to mature box. For a taller formal hedge where you need 60cm or more of height, Osmanthus x burkwoodii is an excellent choice, slightly more open in texture but very hardy and reliably evergreen. Taxus baccata (yew) is a superb long-term choice if you want a different look entirely: slower still to establish but almost indestructible once settled, and its dark green clips beautifully. Lonicera nitida establishes fastest of all and is a reasonable short-term option, but it loses its crisp edge within a season if you miss a cut and can start to look ragged at the base after ten years. One critical point on replanting: do not put any of these into the same soil immediately. The blight spores persist in the soil and in debris for up to six years. Remove as much of the old root material as you can, let the bed rest for at least one full growing season if possible, and consider a top-dress of fresh topsoil before replanting. Our species choice Q&A has more on matching species to your soil.