[rubixs49]

can some please identify what this white fur is on my apple trees is and what to do to get rid of it and if its harmful

ty

[Featherstone]

possibly woolley aphid. I used an organic pest control (basically veg oil) and applied with a soft toothbrush which done the job.

[ghost61]

Definitely woolly aphid.  You can scrub them off with a small scrubbing brush, or spray.

[rubixs49]

is there anything i can use to prevent them coming back.
would these effect the crop/harvest

[gobs]

The badly affected branches you want to get rid off, before applying any treatment.  Aphelinus mali is your biological control agent.