Disease
Box blight
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in April | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September | Watch for in October | Watch for in November |
What it is
Box blight is a fungal disease that has spread widely through British gardens since the 1990s, causing bald, brown patches in hedges, parterres and clipped balls. Plants are seldom killed outright, as the roots are unaffected, but repeated attacks can leave dense, tightly clipped box looking threadbare.
Symptoms
Leaves develop dark brown spots or turn straw-brown in patches, then fall quickly, leaving bare twigs. Look closely at young stems for narrow black streaks, which are the most reliable sign. In humid weather, a white, fluffy growth of spores may appear on the undersides of infected leaves. Box tree caterpillar damage can look similar from a distance, but it comes with webbing, droppings and chewed leaves, and the caterpillars themselves.
Cause
The fungus spreads in water splash from rain and irrigation, and on tools, clothing and newly bought plants. It needs warm temperatures and wet leaves for several hours to infect, so muggy summers bring the worst outbreaks. Spores can survive for years in fallen leaves, and dense, frequently clipped growth stays damp inside and gives it an ideal home.
Control
On dry days, cut out infected shoots well into healthy growth, and carefully gather up every fallen leaf from inside and under the plant, as these are the main source of reinfection. Bin or burn the debris. Clean shears between plants. Feed and mulch to encourage recovery. Badly hit plants can be cut back hard in spring and often regrow. Fungicides offer limited protection and are a last resort only; follow the label.
Prevention
Clip less often and only in dry weather, and avoid overhead watering. Leave space between plants in containers. Quarantine new box away from existing plants for a few weeks. If blight keeps returning, consider tougher evergreen alternatives such as small-leaved holly or Japanese holly for hedging, or box cultivars known to be less susceptible.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: April, May, June, July, August, September, October and November.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.