Question
What insecticide do you recommend for spiders on cotoneaster hedge, some hedge has died , some is covered in powdery mildew.
I think sevin would work in the powder form.

Answer
Shawna:
Spiders by themselves usually do not damage plants.  They are probably after an insect that may be doing the actual damage.  An accurate ID of the insect(s) is essential in management.  Snip off a twig with the "mildew" that is representative of the problem and carry by your local nursery/garden center to get their observations and suggestions.

Regards
Steve