I planted 4 young hornbeam (Carpinus betulus) trees in my garden,
approx 4 months ago. I noticed several weeks ago a sticky surface on
the leaves, which is now dry, but the leaves have what appear to be a
sooty black mould covering them. The leaves are not dropping, but it
looks unsightly, and im concerned it may affect the trees in the
future. When it rains it washes some of the mould off, but then it
reappears, any ideas ? thank you

wrote:

I planted 4 young hornbeam (Carpinus betulus) trees in my garden,
approx 4 months ago. I noticed several weeks ago a sticky surface on
the leaves, which is now dry, but the leaves have what appear to be a
sooty black mould covering them. The leaves are not dropping, but it
looks unsightly, and im concerned it may affect the trees in the
future. When it rains it washes some of the mould off, but then it
reappears, any ideas ? thank you

The good news is that it isn't a disease, but rather some sort of sucking
insect problem. Check thoroughly for aphids or scale, both of which
produce honeydew, a sticky excretion. This is the breeding ground for
sooty mold, a fairly harmless and wash-offable fungus, although a severe
infestation can interfer with photosynthesis. Carpinus tend not to be
bothered much with insect problems - I'd make an assumption yours are
stressed from transplanting or perhaps over-fertilization, both of which
tend to to attract sucking insects that would not normally bother these
trees. BTW, one of my favorite trees, spcially the fastigate form - nice
choice.

pam - gardengal

I planted 4 young hornbeam (Carpinus betulus) trees in my garden,
approx 4 months ago. I noticed several weeks ago a sticky surface on
the leaves, which is now dry, but the leaves have what appear to be a
sooty black mould covering them. The leaves are not dropping, but it
looks unsightly, and im concerned it may affect the trees in the
future. When it rains it washes some of the mould off, but then it
reappears, any ideas ?

The "sticky stuff" is honeydew,the excrement produced by aphids. Sooty mold
grows on honeydew. It will not impact the health of the tree but the aphids
may. You can hose them off with a strong stream of water. Repeated aphid
infestations may require the use of a pesticide.
sed5555