Thankfully the risk is still very small where I’m living in the Cotswolds. But I feel it is just a matter of time before for the box tree moths start to travel West.
The Box tree moth (Cydalima perspectalis) is native to East Asia and became established in the UK in 2011. Stoke Poges in Buckinghamshire has the unfortunate label of being the location of the invasion after a local took a caterpillar to the 2011 Chelsea Flower Show to be identified.
Now the main areas of infestation are London and Essex, but it’s realistic to expect the problem to spread to other areas of the UK soon.
The caterpillar of the moth causes the damage by feeding on the leaves of the Box. Defoliation can be very rapid. They can also attack the bark of the box, causing the plant to dry out and die.
Always be alert for the caterpillars, which are characterised by black stripes with white dots on a light green body with hairs and a shiny head. Other signs to look out for are green balls of ‘Frass’ (waste excreta) and trails of sticky webbing. Remove the caterpillars as soon as you see them to prevent damage. With early detection Box tree moth can be controlled.
The caterpillars can be controlled by spraying with an insecticide. You will need to spray hard to penetrate the protective webbing. The moth’s eggs are also protected by web ‘cocoons’ that stick the box leaves together and offer an good defence against spraying. Personally I try not to recommend using insecticides, except in extreme cases. Their use can have a devastating effect on the beneficial pollinating insects. Best to use an insecticide in the evening when the risk to pollinating insects is at its lowest.
Another solution is Box Tree Moth pheromone traps. They attract and trap the male box tree moth. With no male moths to procreate with the females then the life cycle is broken and no new caterpillars are created to cause the damage.
The pheromone used in the trap will only attract box tree moths so other butterflies and moths should not be affected. And it does not harm beneficial pollinating insects. The main downside is the unpleasant job of regularly cleaning the traps to avoid putrefaction. But this only needs to be done during mid-March and the end of October when the box tree moth is active.
A treatment for box tree moth is Xentari, which is a biological product that is sprayed on to the box to stop caterpillar damage and is safe to use around pollinating insects. This product is now available to buy on Amazon.
In France they are trialling a tiny parasitic wasps. Millions are being released in eastern France with the hope they can kill the box tree moth eggs.
Happy for you to contact me if you are concerned about the threat of the box tree caterpillar to your topiary and box hedging.