Woolly aphid is a black aphid that sucks

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

Woolly aphid is usually easy to spot:

• Between spring and early autumn, affected parts of the trunk and branches are covered with a fluffy white waxy material. This is secreted by the blackish brown aphids
• The thinner bark around old pruning cuts is a prime site for woolly aphid colonies in spring but by mid-summer the insect spreads to younger shoots
• Affected shoots usually develop soft, lumpy growths in the bark as a result of woolly aphid feeding. Such shoots are easily spotted during winter pruning. The swellings can split in frosty weather and create entry wounds for the fungal disease known as apple canker
• Woolly aphid is only found on apple, cotoneaster and pyracantha on other plants the white waxy deposits could be signs of other insects including scale insects, woolly beech aphid or in glasshouses, mealybug

Aphids form the basis of many food chains and it is not unusual to have some of these animals in a healthy balanced garden ecosystem. On tall trees aphids aphids can be considered part of the biodiversity they support; natural enemies will normally reduce numbers by late summer.

• Where possible tolerate populations of aphids; plum aphids often do not affect cropping or future health of the tree
• Check trees frequently from spring onwards so action can be taken before a damaging population has developed
• Use finger and thumb to squash aphid colonies where practical
• Encourage aphid predators in the garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. Be aware that in spring aphid populations often build up before natural enemies are active in sufficient numbers and then give good control
• Research has indicated that earwigs on fruit trees can reduce aphid numbers and in fruit trees they do not cause damage. Providing shelters such as flower pots loosely stuffed with hay in trees can help increase earwig numbers

Woolly aphid overwinters on its host plants as nymphs that hide in cracks in the bark or in crevices around old feeding areas. During the winter months the aphids do not produce the waxy material that gives them the characteristic woolly coating in spring and summer.

In spring, the aphids become active again, mainly around old pruning cuts or other places on the trunk or larger branches where the bark is thinner. They begin sucking sap from beneath the bark, and start secreting the fluffy ‘wool’.

Populations reach a peak in mid to late summer, when the aphids spread onto the younger shoots. Chemicals secreted into the plant as the aphids feed induce lumpy growths in the bark, especially on the younger shoots.

In mid-summer, winged forms of the aphid develop and these will fly off in search of new host plants.