Caterpillar threat to formal gardens

SOME of France’s best-loved formal gardens are in danger from a caterpillar that threatens to wipe out box hedges.

The Box tree caterpillar Cydalima perspectalis, called pyrale de buis in French, has already damaged plants in the Jardins du Luxembourg in Paris and Père-Lachaise cemetery.

Introduced accidentally from Asia, the 4cm green caterpillars can eat their way through the leaves of a box hedge or topiary work in a day and kill a large garden in a week, often leaving the dessicated wood covered in webbing.

Since it was first seen in Strasbourg in 2007 it has spread through 60 departments and gardeners in famous sites such as Vaux-le-Vicomte, Seine-et-Marne, and Chenonceau, Indre-et-Loire, are having to take preventive measures with traps and insecticide sprays.

French agricultural research institute Inra has developed a pheromone trap with Spanish company Sansan and Dutch firm Koppert. Called Buxatrap it will be sold from June as part of its SaveBuxus project.

The moth is white with dark edges to all surfaces of the wing. It lays pale yellow flattish eggs in the heart of the shrub and gardeners should look deep into the plant for any traces. Two or three generations can grow in a year.

However, the first signs are often the appearance of webbing and caterpillars. They are active from April until October.

Young caterpillars are greenish-yellow with black heads, while older ones also have thick black and thin white stripes along the body.