Mike Prager wrote:
Our leyland cypress were at least 7 to 8 years old, quite tall and
growing in the back of the yard (in zone7, North Carolina.) and
were watered by my husband when nec., the rain, a sprinkler system
which came to about 10 feet from them.
Over a period of about 3 years the east side of the plants began
turning brown and getting bare.

The species is known to be prone to diseases. Take a look at
this page:

http://www.ces.ncsu.edu/depts/pp/not...din17/od17.htm

It is not prone to diseases here in our climate.

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Travis in Shoreline (just North of Seattle) Washington
USDA Zone 8
Sunset Zone 5