The woolly aphid (eriosoma lanigerum) appears in the spring on
the bark of some fruit trees - it is common around bark which
has not been cleanly pruned. The aphids are covered in a waxy
substance which makes them look like a fungus or mould.
rub your finger over them, the aphids will be crushed and wet,
which is the proof that it is not mould. The waxy coating makes
them difficult to treat with sprays.
Where the pests are ignored, the bark will develop lumps (noticeable
in winter) which may split in frosty periods, leaving the tree
open to apple cankerHow to Treat Woolly Aphid
If the aphids are noticed early, simply paint them with
methylated spirits, or scrape them off individually. If they are
ignored and larger areas are infected, spray with derris
(available from most garden centres). Failing this, cut the
resulting lumps out from the bark.