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GARDENING NEWS 26 August 2015

BOX TREE CATERPILLAR THREATENS



If you have any box tree plants (buxus) in your garden then a new threat is not far off the horizon. It is the Box Tree Caterpillar (Cydalima perspectalis) and in 2015 it has begun to rapidly spread throughout the South East of England. It is the caterpillar stage of the life cycle which causes the damage and it can be devastating.

The eggs of the moth stage are laid on the underside of box tree leaves, normally in the centre of the plant where they are protected from predators. Unfortunately they are also out of view of gardeners. The eggs hatch out to become caterpillars which eat the foliage at the centre of the plant gradually progressing onto the outer edges.

By the time you notice the damage they are doing they will have reduced most of the inner leaves of the plant to skeletons. Whilst box tree plants are prone to a variety of pests and diseases, the only one which strips the foliage is this caterpillar.

Although the defoliation will reduce the vigour of the plant, it would probably recover the next year. However, at the larvae stage of the lifecycle, they feed off the bark of the plant and it is this which is most likely to kill your Box tree plants.

The pupae overwinter near the centre of the plants where they are protected from the worst of our weather. They hatch out in spring and there can be be between two to four generations per year depending on the local weather conditions.

Box tree moth and caterpillar
Picture courtesy of Hellenic Plant Protection Journal

The caterpillars are around 4cm / 1.5in long when fully developed. They have black heads and are striped green, yellow and black. But don't wait for identification, if you see any caterpillars on your box tree, remove them manually and kill them.

CONTROLLING BOX CATERPILLAR


Manually picking the caterpillars off and disposing of them is the first course of action. If that doesn't work  then sprays containing pyrethrum, deltamethrin or lambda-cyhalothrin offer some control. Avoid spraying when the Box Tree is in flower, normally April to May depending on local conditions.

Box is not the easiest of plants to grow successfully for UK gardeners. It is unlikely to be killed by most pest or diseases but achieving that perfectly formed hedge is more difficult than the average gardener. might think.

An excellent alternative to Box is Ilex crenata 'Dark Green' (a type of holly). Only an expert would be able to tell the difference between the two and the Ilex has several advantages. The first is that it is far more resistant to pests and diseases compared to Box and certainly the Box Caterpillar will not trouble it.

Other advantages of Ilex crenata include leaves which do not turn brown when cut and the ability for the Ilex to grow from bare wood. It is also excellent for topiary and far less temperamental compared to Box. We have negotiated a 10% discount on Ilex crenata 'Dark Green' for you from Victoriana Nursery. If you click on the link here, the 10% will be deducted at the checkout automatically, no need for a code.
 

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