Scale insects

Small fixed bumps on the bark or stems, sticky honeydew and a black deposit (sooty mould): these are scale insects, protected by a shell, that weaken the tree by sucking sap.

How to recognise

• Gently scrape a bump with a fingernail: if it lifts off and leaves a small insect underneath, they are scale insects.
• Look for sticky honeydew and black sooty mould on the leaves below the affected twigs.

What to do

• For a small attack, rub the twigs with a brush and a cloth soaked in soapy water (soft soap).
• Spray an oil (rapeseed or white oil) in late winter to smother the scales and their eggs.
• Cut off and destroy the most infested twigs to reduce the population.

Prevent

• Encourage ladybirds and lacewings, natural predators of scale insects, and avoid excess nitrogen feed, which attracts them.

Trees affected