Pest Alert – Rosellinia Blight on Hemlock
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Rosellina blight on hemlock trees photo by Steven Carroll, Schneider Shrub and Tree.
Rosellina Blight Once thought to be only in the western U. S., the Rosellina Blight fungus is now present in North Carolina. It attacks conifers including hemlocks of all sizes and ages. It can kill small trees (seedlings, saplings, and young trees up to 15-20 feet tall), but it usually doesn’t kill larger trees except in hedges.
Wet cool weather increases disease incidence. We see this disease in young trees and old hemlock hedges in landscapes at the end of cool wet summers. In drier years, the disease will remain mostly dormant.
Photo and slide info by Dr. Matt Bertone, NC State from his IPM update presentation
Symptoms and Signs On larger trees the fungus affects the foliage on lower and inner branches, turning the needles a light brown and matting needles together at odd angles. You will see white fungal threads and black ball-shaped structures on the backside of leaves. Trees eventually will begin to defoliate, dropping needles to the ground.
Spread and Control Thought to spread in the air, the fungus continues to spread and get worse through the summer until early fall when the temperature begins to cool and the humidity is lower. Observation has shown that once the disease is present in a tree, it is likely to continue breaking out each subsequent year unless the cycle is broken by fungicide treatments. It is thought that most general fungicides will suppress the fungus. Keeping trees as healthy as possible by preventing stress and injury and by giving plants everything they need such as fertilizer and appropriate amounts of water will help trees fight off the fungus.
Rosellina blight on hemlock trees photo by Steven Carroll, Schneider Shrub and Tree.