Why is my box hedge going brown?
Separating box blight, box tree caterpillar, winter bronzing and drought, since three of the four look similar and need entirely different responses.
- Difficulty
- intermediate
- Time
- 30 min
- Read
- 3 min
Short answer
Look for webbing and droppings, which means caterpillar. No webbing but dark leaf spots and black streaks on the stems means blight. Uniform bronze-purple across the whole plant in winter that greens up in spring is normal and harmless.
Box has two serious problems in the UK now and one cosmetic one, and telling them apart takes about a minute with a hand lens. Getting it wrong means treating a fungus with a caterpillar spray or cutting out perfectly healthy foliage.
What you'll need
- Hand lens
- Secateurs
- Bags for disposal
- Disinfectant for tools
Step by step
- Look for webbing first.Fine webbing between shoots, small dark droppings, and green caterpillars with black heads and stripes means box tree caterpillar. Part the foliage and look inside the plant.
- Check the stems for black streaks.Box blight produces distinctive black or dark brown streaks on the green stems, along with dark-edged leaf spots and rapid leaf drop, leaving bare stems. There is no webbing.
- Consider the season and the pattern.An overall bronze or purplish cast across the whole plant in cold weather, evenly distributed, that greens up in spring is winter bronzing. It is a stress response, not a disease.
- Check the base and the soil.Brown from the bottom up, with dry soil under the hedge, is drought — very common with box under eaves, against walls or in the rain shadow of a building.
- Treat caterpillar with picking and Bt.Hand pick, cut out webbed shoots, and spray Bacillus thuringiensis into the plant, repeating for each generation from April to October.
- Manage blight culturally.There is no reliable domestic fungicide. Cut out affected material, thin the plant to improve airflow, clear fallen leaves from beneath, never water overhead, and clip only in dry weather.
- Disinfect tools between plants.Blight spreads readily on shears and secateurs. Clean and disinfect between plants and between hedges.
- Do not clip in humid weather.Fresh cuts in warm humid conditions are the main infection route for blight. Clip in dry settled weather and ideally not in high summer.
- Feed, mulch and water a stressed hedge.Box under a wall or a tree is often chronically dry. A mulch and a soak in dry spells prevents a great deal of what gets blamed on disease.
- Decide whether to replace.Repeatedly failing box is often better replaced with Japanese holly, Euonymus 'Jean Hugues', Lonicera nitida or yew, all of which clip similarly and avoid both problems.
Tips
- Webbing means caterpillar. Black stem streaks mean blight. Even bronzing in winter means nothing at all.
- Box against a wall or under eaves is usually thirsty, not diseased.
- Disinfect shears between plants — blight travels on tools more than on the wind.
Common mistakes
- Clipping a blighted hedge to tidy it up — Fresh cuts in humid weather are the main infection route, and the shears then carry spores to every other box plant you touch. Cut out affected material with disinfected tools in dry weather instead.
- Treating winter bronzing — It is a normal cold-weather response in exposed box and it disappears in spring. Some cultivars do it every year regardless of care.
If it doesn't work
Webbing, droppings, stripped stems
Cause: Box tree caterpillar — Fix: Pick off, cut out webbed shoots, spray Bt per generation from April.
Dark leaf spots, black stem streaks, bare patches
Cause: Box blight — Fix: Cut out affected growth, improve airflow, clear fallen leaves, clip only in dry weather, disinfect tools.
Uniform bronze cast in winter
Cause: Winter bronzing, a cold stress response — Fix: Nothing needed. It greens up in spring. Shelter and a spring feed reduce it.
Browning from the base upward, dry soil
Cause: Drought in a rain shadow — Fix: Mulch generously and water thoroughly through dry spells.
Questions people ask
Can box recover from blight?
Individual plants sometimes recover with good cultural management, but blight persists in the soil and on debris and usually returns. Severely affected hedges are commonly replaced.
Is there a fungicide for box blight?
Nothing available to gardeners controls it reliably. Airflow, hygiene, dry-weather clipping and removing fallen leaves are what actually reduce it.
What should I plant instead of box?
Japanese holly for small clipped shapes, Euonymus 'Jean Hugues' for low hedging, Lonicera nitida for fast growth, or yew for anything larger.