Privacy Screens and Plant Disease

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The perfect solution for a fast-growing privacy screen might appear to be Leyland cypress (x Hesperotropsis leylandii), or some species or cultivar of arborvitae (Thuja). But there are two serious problems with this approach. The first is the reliance on any single species or cultivar of plant for an entire, large-scale screen; if an insect or disease becomes established, the entire screen is at risk. A diverse planting provides the best chance of long-term success. The second problem is that the cypress family (Cupressaceae), which includes arborvitae, Leyland cypress, and junipers, tends to be problem prone, with Leyland cypress at the head of the line. In a recent online presentation, the NC State University Plant Disease and Insect Clinic reported that Cupressaceae is the 4th most common group represented in problem samples submitted to the Clinic. As I’ve suggested to many property owners through the years, go ahead and plant a Leyland cypress or two; just don’t plant 50. I would suggest the same for arborvitae such as ‘Green Giant’.
Contact your local Extension office for a list of suggested screening plants for your area. For further commentary on Leyland cypress problems, see the NC Forest Service note, Disease of Leyland Cypress on the Rise.
Diseased tree

‘Green Giant’ arborvitae diagnosed with Botryosphaeria dothidea, a fungal dieback pathogen. Several other ‘Green Giant’ arborvitae in this privacy screen displayed the same symptoms. Landscape stresses such as compacted, droughty, or overly wet soils can predispose plants to infection. Fungicides are of no practical value in this situation.