‘Effective’ ways to remove ‘serious threat’ box tree caterpillars from your hedges

Gardeners' World: Expert on removing box tree caterpillars

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Box tree caterpillars, also called box hedge caterpillars, feed on box plants, specifically hedges, and can take down a healthy plant in a matter of hours. The pests were first found in gardens in the UK in 2011 and quickly became widespread, now found across England, Wales, Scotland and Northern Ireland. The very hungry caterpillars can strip mature bushes of leaves in just a couple of days.

Fortunately, gardening experts at BBC Gardeners’ World Magazine have shared how to identify and deal with these pesky garden pests.

They said: “Box tree caterpillars are a serious threat to box plants – they can completely defoliate them, ruining prized topiary and native box hedges. 

“The caterpillars cause most of their damage between March and October. 

“A box ball can be destroyed within a week if action is not taken.”

Box tree caterpillars are the larvae of a moth, which lays its eggs on the undersides of box leaves. 

The resulting caterpillars create cobweb-like webbing over their feeding area, and devour the box leaves. 

After around a month, the caterpillar forms a chrysalis which emerges as a box tree moth, which then mates, perpetuating the cycle. 

Box tree caterpillars can be a problem from spring to autumn, producing multiple generations. The caterpillars overwinter among box foliage, resuming feeding the following spring.

The experts noted that the signs of box tree caterpillars can be confused with box blight.

They said: “You are likely to become aware of box tree caterpillars when you see the tell-tale webbing, dieback and droppings on your box plants. 

“As the caterpillars conceal themselves deep within the plants, this often becomes apparent when you have trimmed or shaped your plants.”

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The symptoms include webbing, dieback, dropping eggs, moths and stripped bark.

The gardening gurus explained that biological control is an “effective” way to get rid of box hedge caterpillars.

They said: “If the caterpillars are really taking hold, a biological control that contains the micro-organism Bacillus thuringiensis is said to be effective. 

“Treatment needs to be repeated several times across the season, when the temperature is at least 15 degrees.

“Spray thoroughly, coating both sides of the leaves so it penetrates deep into the plants.”

Gardeners can also opt to remove the pests by hand.

The experts said: “You can try to remove the caterpillars by hand if the infestation is small or you only have a few plants.

“However, you will need to do this every day once signs of their presence have been spotted, and check deep within the plant. 

“You can also prune out the stems covered in webbing, using secateurs.”

Insecticides can also be used to control these garden pests, although it is not as effective as biological control.

The gardening pros said: “Insecticides can be used on box tree caterpillars but they are not thought to be as good as the biological control and will also kill other insects. Multiple applications are needed. 

“Do not spray insecticides near plants that are in flower to avoid harming beneficial pollinators.”

Prevention is a great way to ensure box hedge caterpillars never make it into gardens in the first place.

Setting pheromone traps is a useful indicator of the presence of box tree moths so gardeners can take prompt action.

The experts said: “Pheromone traps feature a synthetic pheromone that mimics the one produced by the female box tree moth. 

“The male moths are then attracted to the pheromone and become stuck inside the trap, disrupting the breeding cycle. 

“The traps need to be replaced frequently and are unlikely to catch all of the male moths in your garden.”

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