Answer: Sounds like powdery mildew, but that's not usually a problem with Leyland Cypress. Another possibility is a colony of adelgids which are tiny insects that normally attack hemlock trees in the Pacific Northwest. Without knowing which problem it might be, I'm at a loss to suggest a control strategy. I'd take a sample of the problem into your local cooperative extension office (WSU King County Cooperative Extension, 700 5th Ave Seattle, WA 98101 phone (206) 296-3900?) or Master Gardener Clinic for positive diagnosis. Helpful folks there can provide control strategies.
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