Dealing With Caterpillar
The box tree caterpillar (Cydalima perspectalis) has the capacity to devastate box plants very suddenly. There are reports that this can occur overnight but it is likely that earlier signs of infestation have been neglected and plants have not been inspected on a regular basis. However, once an infestation with the caterpillar has taken hold the voracious insects can do extensive damage very quickly. The more vigilant the gardener is, the better the outcome because when caterpillar attacks are managed at an early stage, the plants will recover quickly with new leaf growth from healthy stems.
Identifying attacks of box tree caterpillar
On close inspection, damaged leaves are present, some partly eaten, others brown. Skeletonised leaves are observed with only their ribs and outer margins intact and there is a characteristic presence of pale-coloured wispy cobwebbing between leaves. Once an attack by caterpillar has been identified, plants should be searched for live insects which should be removed and disposed of. Next, clear away the damaged parts of the plant with a secateur and collect and burn the debris from the ground.
Eliminating box tree caterpillar
Biological agents are the first choice for treating attacks of box tree caterpillar. An extremely effective compound is the bacterium Bacillus thuringiensis which is available on the internet as Xen Tari. Dipel is also available but its use is restricted to professionals. The compound causes damage to the stomach with feeding stopping within an hour and the insect is killed after one to three days. Spraying should be carried out at the first sign of infestation but not in wet conditions, although it remains effective once it has dried. These biological agents are active for up to ten days because they are destroyed by u/v light. They are specific for caterpillars and do no harm to other insects.
Pheromone traps have a role in the identification and control of box moth infestation. Although the number of moths caught in a trap has a small effect on control, the chief benefit is that when moths are seen it is a sign that the infestation is present and the gardener will be extra vigilant in searching for the presence of caterpillars, so that measures to eradicate the pest can be carried out at the earliest time.
A new book
A recently published book has a fully illustrated chapter on measures to control the box tree caterpillar as well as all the other important pests and diseases of box plants:
A Gardener’s Guide to Box; designing, shaping and caring for Buxus.
By Jenny Alban Davies
Price £14.99.
