All over Dublin, and elsewhere in Ireland, Box plants have been gobbled up by hungry caterpilars. Last year (2025) we had dozens of people coming into our shops wondering what had happened to their lovely green plants. Almost overnight, the leaves dispappeared and the hedges were reduced to tatty skeletons.
For anyone who is not a plant expert, 'Box' / Boxwood' / 'Box hedging' is that small-leafed evergreen plant that is often trimmed into a ball, a cone or most often a hedge. Its botanical name is Buxus sempervirens. It is one of the more common garden plants and has been grown in Irish and English gardens for hundreds of years. It is used in many Dublin gardens and also in formal gardens around Ireland. In fact, the world's tallest box plant, at over 12 metres in height (and 300 yreas old), is in the grounds of Birr Castle in Co Offaly. Box wood is prized by craftspeople, carvers and printers: traditionally the wood was used to make printers blocks. For gardeners, its a glossy, evergreen plant that is unbeatable for its density and ability to be shaped or used a hedge.
The positive news is that the box moth caterpilar infestation is not a disease. The plants do not die if their leaves are eaten. The plants remain alive and leaves will grow back. However, if every time the leaves grow back they are eaten again, the plants will eventually run out of steam. The caterpilars hatch from eggs that area layed by fairly inconspicuous box tree moths.
So, there are a couple of things you can do to save / preserve / repair your box plants. If they are currently in good, healthy condition, BE READY for the caterpilars to appear. The first box caterpilars should appear in mid to late March or even in April, depending on temperature and light levels. You may see a sticky webbing in your plants. You might find areas where leaves have been woven together in a small coccoon. As soon as you see damage occuring on the plants, spray them with XenTari. This is what is known as a biological control. It's not a chemical or a conventional pesticide. Its a bacteria that kills only these caterpilars. It is harmless to other organisms or to animals that may eat the caterpilars. Be sure to reach inside the plants and to spray from different angles. XenTari is not that expensive and one sachet covers approx 30 square metres of box plant. If you use it at the right time (ie when there are caterpilars present) then it efficient, fast and effective. One box contains 5 sachets and costs €27.50 That box will do 150 square metres of box hedging, which is a LOT.
As there will be more than one season of box tree caterpilars, be ready to spray again two or three times again during the summer, with a last treatment around September. On a positive note, once you spray you reduce the likelihood of having a major infestation the next time around. Also, if your neighbours are attentive, the 'infestation' of the caterpilars / moths will diminish as the prevalance of them in your neighbourhood will decrease. 2025 was an especially bad year, because most people were taken by surprise and too few were prepared.
If your box plants were fairly heavily knocked back last year, as many were, there is still hope. They may look twiggy and bare, with just the occasional grean leaf. With the right care and a bit of attention, they can be revived. Shake the plants and remove dead leaves from under them (there could be a new generation of caterpilars in there). Dispose of the leaves. Spread fertiliser along the base of the plants: either a nitrogen-rich fertiliser specifically for box plants (which we sell in our Dublin shop) or a well-rotted manure such as Gee-Up, also available from us. This will help the plants to re-leaf, and give them the strength to thicken up and produce new shoots.
If you attain this, your job will be to keep a lookout for the caterpilars and to have the XenTari at the ready.
Final note: there are other treatments to help protect your plants from the box moth caterpilar. Neem Oil can be applied as a spray, mixed with lukewarm water and a few drops of washing up liquid. Neem oil is a natural insecticide and natural fungicide. It needs repeated used to be effectiv. We find it to be an excellent once-off treatment against greenfly and a useful, safe treatment for many houseplant pests. There are also products such as 'Bug Clear' or other natural pesticides that use plant-based chemicals that are harmless to the environment. Neem oil and 'Bug Clear' are available in our Dublin shops (along with many other plant care treatments).
