What's eating my leyland cypress?

Leyland Cypress is one of the most pest-prone large conifers in UK and US gardens. Bagworm is the worst insect pest in the US, while the cypress aphid devastates hedges in the UK. Seiridium canker fungal disease is the single most destructive problem overall, causing irreversible branch death.

Silken bags covered with foliage fragments hanging from branches; larvae strip needles causing brown patches, branch death, and full tree loss in heavy attacks. Hand-remove bags in winter before eggs hatch; spray Bacillus thuringiensis (Bt) on young larvae in late spring; use permethrin or spinosad for larger larvae.

Large brown colonies on stems; yellowing and browning of foliage sections; sooty mould on honeydew; can kill whole hedge sections quickly. Spray with insecticidal soap or pyrethrin; systemic neonicotinoid drench for severe infestations; encourage natural predators (parasitic wasps, ladybirds).

Speckling and bronzing of inner foliage in cool spring/autumn; webbing visible; needle drop weakens the hedge. Apply forceful water sprays; miticide (abamectin or bifenazate) in early spring and autumn when mites are active; avoid excess nitrogen.

Dead brown branches with resin-soaked cankers at the base; spreads rapidly under heat and drought stress; no cure once a branch is infected. Prune infected branches well below the canker with sterilised tools; destroy cuttings; improve irrigation and spacing; no fungicide is effective post-infection.