Dealing with Box Tree Caterpillar

Box tree caterpillars are the larvae of the box tree moth and can rapidly strip the leaves from box hedges, topiary and other Buxus plants. Look for chewed leaves, fine white webbing, black or green droppings and green caterpillars with black and white markings. If caterpillars are present, act promptly and continue monitoring the plant throughout spring, summer and autumn.

• Key facts
• What is box tree caterpillar?
• How to identify box tree caterpillar and infestation
• Box caterpillar or box blight?
• Box tree moth lifecycle
• How to control box tree caterpillar
• How to prevent box tree caterpillar returning
• Frequently asked questions
• Recommended products

Box tree caterpillars are the larvae of the box tree moth, Cydalima perspectalis. They feed primarily on box plants, including Buxus hedges, borders, topiary and container-grown plants. The adult moth does not eat the foliage, but its appearance can warn you that eggs and a new generation of caterpillars may follow.

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 affected 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.

The clearest signs of Box Tree Caterpillar are eaten leaves, white webbing and caterpillars hidden inside the plant. Check for:

• Chewed, ragged or skeletonised leaves
• Fine white webbing between leaves and stems
• Greenish caterpillars with black heads and dark stripes
• Black or green droppings, known as frass, caught in the webbing
• Brown, bare or thinning sections of the hedge
• Leaves webbed together around overwintering caterpillars
• Bark being stripped from stems in a severe infestation

Part the foliage and inspect the centre of the hedge, the underside of leaves and recently clipped areas. Young caterpillars often begin feeding deep inside dense growth, so the infestation may be more advanced than it appears from the outside.

Box Tree Caterpillar damage involves visible feeding, while box blight is a fungal disease that causes leaf browning, leaf loss and stem dieback. Webbing, droppings and chewed leaves strongly suggest caterpillars; black streaks on stems without feeding damage are more consistent with box blight.

Box tree caterpillars are usually active from early spring until autumn, with two or more generations possible in a year. Mild weather can bring feeding forward or extend activity later into the season.

• Winter: Small caterpillars overwinter between leaves held together by webbing.
• March to May: Overwintered caterpillars become active and begin feeding.
• May to June: Caterpillars pupate and the first adult moths emerge.
• Summer: Moths lay eggs and further generations of caterpillars hatch. Damage can increase quickly.
• September to October: Later caterpillars feed before creating shelters in which to overwinter.

The best way to control box tree caterpillars is to identify them early, remove visible pests and webbing where practical, and apply an appropriate treatment to active caterpillars according to its label.

Step 1: Inspect the entire plant

Part the branches and check inside the hedge, beneath leaves and around webbed sections. Confirm that caterpillars are actively present before selecting a treatment.

Step 2: Remove visible caterpillars and webbing

On small plants or light infestations, remove caterpillars by hand and prune out heavily webbed material. Dispose of infested material responsibly rather than adding living caterpillars or pupae to home compost.

Step 3: Choose an appropriate treatment

Control of Box Tree Caterpillar can be effectively achieved using either contact or systemic insecticides.

Dipel DF contains Bacillus thuringiensis subsp. kurstaki, a biological insecticide that targets feeding caterpillars. The treated foliage must be eaten, so thorough coverage of the leaves, including growth inside the hedge, is important.

Decis ProTech is a pyrethroid insecticide that can provide rapid control where its label permits. Because broad-spectrum insecticides can affect non-target insects, it should be used carefully and only in accordance with the product label.

Shop Box Tree Caterpillar & Other Plant Pest Control

Step 4: Monitor and reassess

A single treatment does not prevent moths laying more eggs later. Continue checking for new webbing, feeding damage and young caterpillars, and only repeat treatment in accordance with the product label.

You cannot guarantee that box tree caterpillars or moths will not return, but regular monitoring can help you catch each new generation before serious damage occurs.

• Inspect box plants regularly from early spring to autumn.
• Check the centre of dense plants, not only the outside.
• Remove overwintering webbed leaves where practical.
• Following an increase in moth catches, inspect plants closely for eggs and young caterpillars.
• Continue checking after treatment because eggs and pupae may remain.
• Avoid allowing the centre of the plant to become excessively dense.
• Clean up dead leaves, frass and pruned material around affected plants.