Question
We have an old crab apple tree and noticed white fluffy fungus which we believe could be bark scale attached to two stumps and  bark at the bottom of the tree.  Someone advised we spray it with anti-fungal spray which we did last year but it hasn't made much difference and has, in fact spread a little further this year. What can we do to eradicate this problem?

Answer
If it is an insect (scale)  you will need to spray it with an insecticide. I am not familiar with the Insecticides that maybe available in the UK but if you have tree or plant nurseries check with them for an insecticide for aphids or scales. Ones in the US are Orthene and horticultural oils for the scales. The white fluffy sounds like an aphid. Touch the fluffy and if it moves it is an insect. IF it does not it maybe Powdery mildew a fungi.

Fungicides for control of powdery mildew :
  Banner MAXX? Immunex?
  Benomyl? Benlate
  Folpet? Phaltan
  Bayleton? Strike?Triadimefon
  Funginex? Triforine
  Triact? Rose Defense? Neem oil
  Pipron?
  Phyton 27? copper sulfate
  Rubigan AS?
  Cooke's?wettable, Safer?Garden Fungicide, Microthiol Special?Sulfur