Forgive me if this is a recurring question, or indeed a very obvious one. I
have a few small trees which I am growing on in large pots prior to planting
out. On several I have noticed a white sticky substance underneath the leaves.

Is this a fungus or is it a residue from some hideous insect? More importantly
how do I cure it? (The infected trees do not look in the best of health, ie
drooping leaves etc)

Any help would be greatly appreciated

John