Help with brown branches

I have five Itailian Cypress planted in my backyard. The bottom branches have turned brown and the brown is beginning to advance up the trees. They are about 24 feet tall and the brown is 5-6 feet up from the bottom and rising. They receive morning sun, but are blocked by two 50 year old oak trees by noon time. Is it the lack of sunlight that is causing this? I would rather remove the oak trees than lose the cypress. My husband had raised the sprinklers around them to 4-5 feet and I thought this might have something to do with it and have now lowered them to soil level.

 

You aren't registered so I don't know where you live. Under those circumstances I can't comment on the sprinkler and water situation as you could be in a drought area or in an area where the cypress doesn't need all that water. Take a look at this site and scroll down to 'Winter Browning' and keep going for help.
http://www.agr.gc.ca/pfra/shelterbelt/evergreen_e.htm

Newt