Botanic Garden >> Gardening > >> Question and Answer >> Plant Species >> Conifers

Leyland Cypress Top Dieback: Weevil Diagnosis and Treatment

20-foot Leyland cypress (12 months post-planting) in Washington DC area shows top 5 feet dead. Owner seeks rescue options.

Diagnosis: Pales Weevil or Similar Bark Beetle

Top-down death with a transition zone suggests a trunk-boring insect. Look for:

Slight swelling or sap flow at live/dead boundary
Small entry holes with frass

Treatment Protocol

Cut dead top at living tissue (green cambium).
Spray trunk with Onyx (bifenthrin) or similar bark beetle preventive.
Protects through growing season.

Long-Term Form

A lateral branch near the cut will assume dominance as new leader, creating a permanent crook. Several years to restore apical form. Foliage diseases (Seiridium, Bot canker) cause scattered branch death—not clean top kill.

Conifers: Leaning Saguaro Near Irrigated Lawn: Root Rot and Professional Move; Leyland Cypress Summer Planting Shock: Mulch, Deep Watering, and Guarantee Leverage; Transplanted Leyland Cypress Browning: Canker Diseases and Management; New Leyland Cypress Browning at Base: Planting Stress, Not Spider Mites; Repeated White Pine Death in One Spot: Investigating Site Problems; Moving 15–20 Foot Leyland Cypress: Root Ball Requirements and Pruning Alternative; Reviving a Dying Canela Plant; Saving Leyland Cypress from Transplant Shock and Pest Damage; Treating Brown Patch in New Dwarf Fescue Sod; Leyland Cypress Decline in Shade: Cercospora Fungus

Garden Articles

Leyland Cypress Fertilizer: Slow-Release Organic, Soil Test First

Fertilizing Leyland Cypress: Timing and Product Selection

White Ash Tree Decline After Bark Damage: No Cure, Monitor for Borers

Pruning Overgrown Mophead Cypress: The Golden Rule — Never Cut Into Old Wood

Leyland Cypress Top-Down Browning: Root Issues and Site Evaluation

Arborvitae 'Golden Biota' Dying in Shade: Diagnosis

Topping Leyland Cypress: Managing Height and Stability in Mature Trees

Plants

Honey Ash Tree Top Dieback: Signs of Internal Decay

Grafted Cactus Basal Rot: Top Scion Likely Lost Too

Drastic Leyland Cypress Height Reduction: Not Feasible

Cedar Hedge Top Dieback: Grafting Not Viable, Replacement Recommended

Recovering a Weeping Willow After Ice Storm Damage

Topping Leyland Cypress Hedges: What You Need to Know

Leyland Cypress Dieback: Seridium Canker from Drought and Cold