Leyland cypress on the east coast are frequently plagued by bagworms and a variety of fungal problem including several cankers and root rots. Depending on what exactly the problem may be, it is sometimes treatable and other times, removal and replacement is the only solution.
As common as these problems seem to be, I'm surprised the county extension agent wasn't more familiar with them and could give you better advice. This link may help clarify your problem:
Anyone else experienced their Leland Cypress becoming ill? Branches are dying. So far we have followed each suggestion from the county agric. guy, the disease seems to continue spreading. Any clues? The agric. guy worked on the hypothesis that it must be something known to effect cypress. We have used all the antidotes for these things. He admitted he did not know what the problem is, and agreed that they are sick and branches are dying. Any help out there? J. Davidson zone 7, NC
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