Dealing with Box Tree Moth/Caterpillar

Key Facts

• Common Name: Box Tree Moth / Caterpillar
• Scientific Name: Cydalima Perspectalis
• Areas Affected: Buxus Hedging
• Signs of Infestation: Defoliation
• Most Active: Late July - End of September

How to Identify Box Tree Caterpillar / Moth

The Box Tree Moth causes no damage itself; however, early identification of the adult moth will give crucial time to prepare for the emergence of the larval stage or the Box Tree Caterpillar.

The Box Tree Moth has a wingspan of up to 40mm and a generally white with a brown to purple/brown wing margin. Typically flies from late July through to the end of September although this can be effected by environmental conditions, a warm March/April will allow for early migration and pupation of the moth.

The Box Tree Caterpillar or larval stage is light green, up to 4cm long and identified by black stripes with white dots, long individual white hairs which protrude stiffly from the body and a shiny black head.

Typically, there are two generations per year although in years with mild springs and autumns there can be as many as four. Larvae will overwinter in cocoons spun with fine white webbing and leaves of box plants.

Symptoms to look out for

Box Tree Caterpillars feeds on the leaves and bark of buxus species causing defoliation, occasionally leaf skeletons will be left.  Large populations are able to completely remove all foliage, once this food source has been exhausted the subsequent feeding on the bark will cause plants to dry and out die. Box Tree Caterpillars can he hard to find, typically their presence is identified via the webbing they leave between branches.

The adults cause no damage the only ‘symptom’ of their presence will be their eggs. These are pale yellow and grouped in tight clusters.

How to control Box Tree Caterpillar / Moth

The adults are good flyers and highly mobile, control options are typically targeted to the larval stage and insecticides are rarely affective at preventing egg laying. Box Tree Moth Activity can be monitored using pheromone traps. Trapping will also help to remove some of the mating population, however, this should not be relied upon as a control measure and purely as an indication of when an insecticide should be applied.

Control of Box Tree Caterpillar can be effectively achieved using either contact or systemic insecticides. Pyrethroid based insecticides such as Decis will rapidly kill Box Tree Caterpillar, but should only be used as a last resort due to their impact on non-target species. A bio-pesticide with the active ingredient Bacillus thuringiensis, such as Dipel, should be used in the first instance. These insecticides are specific to caterpillar species are have little to no impact on non-target insect life. It requires a fine spray coverage over all leaf surface areas as these insecticides require ingestion by the caterpillar in order to work. Dipel targets only Lepidoptera (caterpillar species) however re-sprays will likely be necessary.

Regular inspection of the hedging for eggs, ‘frass’ (caterpillar droppings) and damage to leaves will be necessary to warn of further infestations.