I have dead areas o my conifer fence my neighbours side however does not

Hi, possible cause could be the conifer aphid, this has been a major problem over the last ten years or so, being a gardener I have come across this many times, on large conifer hedging you will notice large patches/swathes of dieback, and at this time of the year the early signs can be seen, the lovely deep green starts to go a sickly yellow colour and by April/May this dies back and brown patches can be seen, unfortunately once dieback occurs then you will not get any regrowth, check about 4/5 inches inside the hedge for sooty mould and big fat greyish aphids, control I have found is to spray with pro ado bugclear about three times a year, however I think they have taken this product off the shelves so you will need to look for an alternative, it has been noted too that thrips can also be a problem, confers with the conifer aphid can look patchy on one side whereas the other side can be ok.