Box Tree Caterpillar (2)

Here are a few tips on what to do if you find the Box Tree Caterpillar in your garden…
Pesticides
Fortunately, there are many insecticides available that will kill the Box Tree Caterpillar. Look for products containing pyrethrum, deltamethrin or lambda-cyhalothrin. Follow the instructions, ensure you achieve total coverage and repeat spray as instructed. Two applications a fortnight apart may do the trick – but keep checking.
Organic gardeners should look for pyrethrum insecticides as the active ingredient – made from dried Chrysanthemum flower heads – is natural.
NB: Over-the-counter pesticides are an effective and workable solution for smaller Box hedging and Box growing in pots and containers. However, if you have more extensive Box hedging and/or specimens to which you are particularly attached, it is worth consulting a professional. They’re equipped to spray large areas and are licensed to use more powerful pesticides than those available to the general public through garden centres etc.
Birds
Many birds eat caterpillars – including the Box Tree Caterpillar– and encouraging these birds into your garden from April-October will offer an extra line of defence. Hang nuts, fat balls etc. near to your Box. This will help, but can’t replace regular checking.
* Including Tits, Finches, Thrushes, Robins and Warblers.
Hand Picking
If you catch an infestation right at the start, hand removal is an option. But once a colony of Box Tree Caterpillars is established, you will probably need to adopt more aggressive measures.
Biological controls
Biological controls are gaining popularity to counter a wide range of garden pests and can offer an effective solution…
Nematodes: Generally, a specific pest requires a specific control and in the case of the Box Tree Caterpillar it’s a nematode (a microscopic worm) called Steinernema carpocapsae (pictured above, considerably magnified). A quick Google will throw up mail-order suppliers. They are best applied when the weather is overcast and cool.
Pheromone traps: The pheromones used in pheromone traps also have to be species specific and we are unaware of traps designed to lure the Box Tree Caterpillar. In any case, the traps are more effective as a monitoring aid than as a cure.
Reporting
The RHS is monitoring Box Tree Caterpillar distribution and has asked gardeners to report its appearance to them at Entomology, RHS Garden Wisley, Woking, Surrey GU23 6QB or. Either way, please include your postcode.