There’s a creepy serial killer hanging around in UK gardens – and it’s got everyone on edge. I’m not talking about the knife-wielding kind, but one that will munch all the way through your box hedge until it’s completely naked!
The box tree caterpillar
The box tree caterpillar is fairly new to Britain, having been introduced around 2007 and first spotted in private gardens in 2011. However, since its arrival, it has caused many gardeners headaches, as well as devastating our wild Buxus hedges, too.
This caterpillar feeds exclusively on Buxus shrubs and trees, specifically the leaves and shoots – so you can see why it has made its home in the UK! We’re a nation of hedges! It can be found across the UK and Ireland, but is particularly prevalent in the counties surrounding London, and in the South East – so much so that gardeners in these areas will likely see recurring infestations throughout the near future.
The life cycle of a box tree caterpillar
Despite its devastating effect, the box tree caterpillar only lives around 45 days. First, the box tree moth lays its eggs on the underside of the box leaves, then the eggs hatch and the caterpillars eat leaves, producing a cobweb-like webbing over their feeding area. If you see your Buxus covered in this webbing, this is a tell-tale sign that you’ve got a box tree caterpillar infestation.
After around three to four weeks, the caterpillar will spin itself a chrysalis and transform into the box tree moth. The cycle then begins again.
Why box tree caterpillar populations thrive in the UK
Unfortunately for us, there are no natural predators of the box tree caterpillar or moth in Northern Europe. This is because the insect is a native of south-east Asia, and therefore its composition is not appealing to our birds or larger insects (one exception is the Asian hornet, which also naturalised in Europe having originated from Asia, and exists in warmer regions such as the south-west of France).
So why does it like Buxus? This plant is not only found in Europe; it occurs naturally in Africa, parts of South and Central America, and parts of Asia. The genetics of the European and Asian species are very similar, which may be why the caterpillars, having come from Asia, are quite happy to munch on our hedges.
How to get rid of box tree caterpillars
There are many methods that gardeners have used to attempt to get rid of box tree caterpillar populations from their prized hedges.
Some have the patience to pick individual caterpillars off the plants and kill them before they get the chance to eat too much of the box (although this is a very laborious and somewhat grim task if you feel guilty about killing insects).
These traps feature a synthetic pheromone to mimic that produced by the female box tree moth. The male moths are then attracted to the pheromone and become enclosed inside the trap. Although this only captures the male moths, it disrupts the breeding cycle. However, the drawbacks of these traps are that the traps need to be replaced often, and it does not guarantee the entrapment of all male moths in the area – some may still settle on your hedges and mate.
These are not recommended due to their impact to other beneficial species such as bees.
Bacteria called Bacillus thuringiensis are often sold online as a treatment for box caterpillar. However, this type of treatment should only be used by professionals who have been trained in its use.
The natural way to protect box plants
If you’re looking for a natural way to get rid of box tree caterpillars and moths, then natural pesticides are the way forward. Richard Jackson has just released a Box Plant Health ‘Cleanse & Shine’ treatment, handmade in the UK with pure essential plant oils. These oils deter caterpillars from eating the leaves of the plants on which it is sprayed, while cleaning and shining the leaves for a healthier-looking Buxus.
The treatment also works on Buxus shrubs and trees that have already experienced an infestation. Regular applications suppress the infestation and allow the plant to recover – which it should do, as caterpillars do not eat the bark or roots of this plant.
The Box Plant Health ‘Cleanse & Shine’ is 100% natural and chemical free, and safe for children, pets, the environment and wildlife. It is available as a ready to use spray (£9.99) and a 500ml concentrate (£12.99) which makes 10 litres of diluted spray.
The product has been independently tested by independent entomologist Dr Ian Bedford, who said, ‘having used the product product on the box balls in my garden over the summer months, the plants not only looked tremendous, displaying clean and glossy leaves, but the damage being caused by box moth caterpillars was effectively stopped.’
Other major invasive species and how to control them
UK gardeners have seen the intrusion of many invasive species over the years. Here are just a few to watch out for:
Spanish slug – Considered a pest not just in newly inhabited regions, but also in its native country of Spain, this slug is considered to represent a potentially serious threat an invasive species which could negatively affect agriculture, natural ecosystems, human health or commerce.
Spanish slugs are hermaphrodites and lay hundreds of eggs, so a single slug can start a massive infestation. One of the best ways to control these infestations is to encourage natural predators into your garden (such as birds, frogs, toads and hedgehogs), or use barriers around your plants and crops, such as copper, slug fences and slug paint. Alternatively, Richard Jackson also has an effective slug and snail control formula that is approved for organic gardening.
Red lily beetle – Indigenous to parts of Europe and Asia, the first major colonies of this beetle established in the UK around 1939, and spread rapidly in the 80s. The beetle eats the leaves, stem, buds, and flowers, of lilies, fritillaries and other members of the family Liliaceae.
Treat plants during the growing season, as these beetles overwinter away from the host plants. Beetles can be removed by hand before populations establish, or sprayed with Grazers G4, which is environmentally safe.
Western flower thrips – These very small, thin insects are native to the southwestern US, but have spread to Europe, Australia and South America. It feeds on over 500 different species of host plants, and can devastate fruit, vegetable and ornamental crops.
Deter these thrips by growing non-host plants around crops, or use biological pest control such as the fungus Metarhizium anisopliae.
Horse chestnut leafminer – This moth species attacks horse chestnut trees, and was first spotted in outbreaks near Yugoslavia in 1984. Since then, thanks to vehicular transport, the moth has spread rapidly across Europe, including the UK.
Horse chestnuts do grow back healthily the season after an infestation; although if you want to keep your trees infestation-free, try raking up and burning fallen leaves to kill any larvae. The use of pesticides are not advised on large trees.
Have you found box tree caterpillars on your Buxus? Let me know how you dealt with them in the comments below!
Michael has been involved with gardening and plants since he was just five years old. He is a self-professed Plant Geek, and was listed in the Sunday Times top 20 most influential people in the gardening world, thanks to his plant hunter role at Thompson & Morgan.
Michael was responsible for new plant introductions such as the Egg and Chips plant and the FuchsiaBerry and keeps busy travelling the world in search of new plants as well as lecturing worldwide, including stints in Japan. He is very active on social media – so why not give him a follow at @mr_plantgeek or Facebook. You can also listen to The Plant Based Podcast with Michael and co-host Ellen-Mary on iTunes, Spotify and Google.