How to control box tree caterpillar
Box tree caterpillar larvae feed on the young leaves of box, and are even able to strip the bark of twigs. We saw extensive damage throughout last year, visible mainly on box topiary and hedges — this is bad news, as excessive emergence of box tree moth tends to continue for a few successive seasons, and can weaken box trees.
Box tree moths overwinter among the leaves, webbed together as tiny caterpillars. When the weather warms up during March - April and young leaves begin to emerge, the caterpillars start feeding. As they strip leaves from the plant, they leave behind a trail of white webbing — this is when the damage becomes apparent.
Here are 3 simple ways to reduce the risk of damage to box trees
Keep an eye out for young caterpillars, and if practical remove them by hand
Encourage biodiversity in the garden, as birds, wasps or ants will all act as natural predators to caterpillars
Try to use mixed nematode biological control
For further tips, see the RHS website for what can be done to protect against the damage of box tree caterpillar.