The West Gatehouse and Llanthony Road by Dr Chris Barnes
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May 30, 2024How do you solve a problem like Box Moth? by Dr Chris Barnes
How do you solve a problem like Box Moth?:
Across the country, gardeners are pulling their hair out attempting to deal with the present issues in keeping their box hedging healthy. Despite being used for hundreds of years within gardens, box plants are now facing a significant problem. Since our medieval courtyard garden was put onsite in 2021, our volunteers have been faced with a significant fight to keep the 400 box plants within it healthy. Unfortunately, this issue has ultimately forced us to remove all 400 plants and start the laborious and costly task to replace them with another plant that fits within our garden - a recreation of a medieval physic (medicinal herb) garden where everything found within it has a historical use as medicine or in the kitchens. This blog will outline the current issues surrounding box plants, our ‘Royal’ replacement, and reflect on the tremendous work our volunteers do in the gardens and grounds at Llanthony.
Box Hedging and its History
Box, Boxwood, or Buxus, is historically one of the most popular low hedging species. It is a native evergreen that is hardy, slow-growing, compact, and dense with oval leaves formed on short stalks. These qualities make it ideal for borders, edging pathways, knot-gardens and have also seen it used for topiary.
Box leaves (Buxus sempervirens).
Shaped box hedging.
Box has been very popular throughout history. It appears within Roman literature, and sprays of the plant have been found within Roman burial coffins within Britain. In the Middle Ages the evergreen boughs were used as a Christmas green and, particularly in Northern Europe, it was used as a substituted for palm on Palm Sunday. In the sixteenth century, the use as low edging for garden beds became common practice, and for that reason and purpose it was planted within our garden.
Box Blight and the Box Moth
Box is relatively unfortunate to have two separate issues to significantly impact the plant’s health. Whilst both Box Blight and the Box Moth/Caterpillar are decimating Britain’s box plants in a similar fashion, they are two very separate issues.
Box Blight
Box Blight has been an issue with box for many years. It is a common fungal disease that can destroy them. At first, the disease causes brown and bare patches on the plant. Untreated, it eventually spreads as the plant dies back, and eventually dies. To manage it effectively, box blight should be caught early. Whilst there are no known biological treatments, there are chemical controls, such as fungicides, that can be applied to the plants, although these are largely ineffective. Badly infected plants should be dug up on a dry day and destroyed, whilst smaller infections can be treated by effective pruning. All prunings from an infected plant should be destroyed and not composted to minimise the chances of box blight spores surviving and contaminating more plants.
The Symptoms of Box Blight on Box.
Image: M. Borden, CC BY-SA 3.0.
The Box Moth and Caterpillar
The Box Tree Moth and Caterpillar (Cydalima perspectalis) is the particular issue that we have fought for two years within our courtyard garden. It is an invasive Asian species that was first recorded in the British Isles in 2008. First spotted in Kent, the species has spread and is now well established in the London area, surrounding counties, and now the whole or Southern England.
The larvae, or caterpillars, of the moth cause severe defoliation, solely feeding on box plants, and is evidently becoming a serious insect pest problem throughout the nation’s gardens. The caterpillars are greenish yellow, with black heads.
A Box Tree Caterpillar (Cydalima perspectalis)
Box Tree Caterpillars (Cydalima perspectalis).
The adult moth usually has white wings with a faint iridescent brown border. However, they can also be either completely brown or clear. Female moths lay pale yellow eggs on the underside of box leaves. These then hatch into the caterpillars that cause the devastation before developing into pupae, which are concealed in a cocoon within the webbing. There are two or three generations per year, appearing between April and September.
The Box Tree Moth (Cydalima perspectalis).
The symptoms of an infestation includes defoliation, webbing, and finding caterpillars on box plants. Left untreated, they will completely decimate the plant. Management of the infestation includes checking the box frequently from early spring onwards to detect the issue before a damaging population has developed. The use of pesticides is not recommended by the Royal Horticultural Society, as they are likely to reduce biodiversity, including natural enemies, impact soil health, and have other adverse effects on the environment. The only proven non-pesticidal treatment includes the removal of caterpillars by hand. There are some reports of mixed nematode biological control having some effect on the caterpillars, whilst some garden birds have been noted to feed on the caterpillars, although it is not clear if this predation will result in a reduction of moth numbers.
The effect of box moth: a row of completely defoliated box within our courtyard garden.
Our 400 box plants were all eventually infested, despite two years of dedicated caterpillar removal, and it was eventually decided to replace them in phases.
Hedge Germander: A ‘Royal’ Replacement
After some debate regarding a replacement plant, we eventually settled on Hedge Germander (Teucrium x lucidrys) as being a worthy replacement. There are a number of plants that have been cited as alternatives to box. These include, but are in no way limited to: Yew, Japanese Holly, Mock Privet, Germander, Osmanthus, Euonymus, Hebe, Lavender, Portuguese Laurel, Barberry, Wire Bush, and Rosemary. After careful consideration, Hedge Germander was identified as the best choice for our garden.
The plant is a fully hardy evergreen that makes a low, neat, flowering hedge. The coloured flowers of small rose-pink flowers in mid to late summer matches our garden’s colour scheme, and they are also attractive to bees.
160 young, pot grown, Hedge Germander (Teucrium lucidrys).
Hedge Germander in a Knot Garden (Image: Cultivar413, CC BY 2.0)
Germander also had historical uses, fitting the theme of our medieval courtyard garden. John Gerard’s The Herball (1579) describes germander’s medicinal uses. Firstly, the plant could be boiled in water and drunk to treat ‘all obstructions or stoppings’, including shortness of breath, coughs, or urine. The leaves could also be ground, mixed with honey, and strained before putting the concoction into the eyes to improve vision.
The Vertues of Germander in Gerard's 'The Herbal' (1579).
The ultimate decision to go with Hedge Germander was vindicated when we subsequently found out that the plant has been nicknamed ‘A Royal Choice’, as it replaced the diseased box hedges at Highgrove.
Our volunteers started replacing the box with the germander in early April, replacing 160 plants over a few hours. Thankfully, the plants have taken to their new surroundings well. Next spring we intend to replace around 200 more plants, hopefully getting us close to replacing them all.
Some of the Hedge Germander planted within the border.
One of our volunteers planting the Hedge Germander.
We rely on the dedication of our volunteers and the support of the public, for whom the garden was intended, for the maintenance of the grounds and gardens. Please consider either volunteering to help us within our gardens and grounds or donating towards their upkeep. Without the support of the community, these wonderful spaces wouldn’t exist.
