THIS week, rather than focussing on a plant, I have chosen to look at a serious and ugly problem in our gardens that seems to be on the increase, despite our recent harsh winters.

Woolly aphids (Eriosoma lanigerum) have been with us since the late 18th century when Sir Joseph Banks first reported their presence in London. They were thought to have been accidentally imported from North America and are still sometimes referred to as the ‘American Blight.’

Distinct colonies of small brown aphids, covered in a white woolly wax, form in spring and early summer on older branches, becoming larger as the summer progresses.

Their favourite plants are apples, crab apples, cotoneasters and pyracanthas and they can sometimes even live on the roots of these plants, sucking sap and gradually reducing the vigour of infected plants.

Irregular swellings build up beneath the colonies and these crack open eventually, allowing an entry point for fungal and bacterial diseases to further damage the host plant.

The use of modern organic, fatty acid insecticides can reduce individual colonies if applied directly and pruning out badly infected stems can help.

On larger trees jet-washing colonies can be very affective. Scrubbing colonies with soapy water is another option.

A parasitic wasp. Aphelinus mali was introduced in the south of England in the 1920s and can have a reducing effect on infestations as can ladybirds, hoverfly larvae and lacewings, although these may well be killed if chemical insecticides are used.