Hi,

I have a 4m high by 9m long conifer hedge. It is either a leylandi or
thuja type, although I have done some research I cannot be exactly
sure.

The hedge is made up of 4 trees, and since its last pruning about 6
months ago (which I did not do), some brown patches have appeared,
majority on 1 tree, slightly on another and none on the other 2.
I have researched the potential cause of the browning, and know it
could be due to many causes, and that it may never recover. One of
these could be some kind of insect infestation.

In the scenario of an assumed insect infestation I was thinking of
getting some insectiside and spraying the hedge. I am under the
opinion of spraying it for the sake of it will at least eliminate an
insect cause, even if not actually present.

I haven't got a clue what type of insectiside to use or what
equipment. Also the potential side effects on the hedge itself,
flowers and other plants in the same soil, animals and children.

Can anyone give me any advice?

Thanks,

James