What attacks cedar: pests and diseases the sources name
A register of the root disease of Lawson cypress, the cedar rust fungi on eastern red cedar and juniper, and the leaf-mining moth of eastern white-cedar, from Forest Research, the Morton Arboretum and Natural Resources Canada: which tree each row names, where it is recorded, and where the full profile is.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. Each row names its source, all read on October 9, 2026. Where this site has a full profile, the row links it. The word cedar covers unrelated trees in these sources: eastern red cedar is a juniper (Juniperus virginiana), western red cedar and northern white cedar are Thuja, and Lawson cypress is Chamaecyparis lawsoniana. Each row says which one the source means. The trees are on the eastern redcedar and northern white cedar pages.
The register
| Agent | What the sources record |
|---|---|
| Phytophthora lateralis, a root disease. Full profile | Kind: Water mould, a fungus-like pathogen Hosts: Forest Research says it mostly affects Lawson cypress (Chamaecyparis lawsoniana) and that few infected trees recover. It lists a wider host range that includes western red cedar (Thuja plicata), northern white cedar (Thuja occidentalis) and Pacific yew. Where and status: Forest Research says it is present in all four countries of the United Kingdom, more prevalent in Scotland and Northern Ireland than in England and Wales, and also reported from the Republic of Ireland, the Netherlands, Belgium, France, the west-coast states of the United States and Taiwan. It lists it as notifiable in the plant trade. |
| Cedar rusts, Gymnosporangium species including cedar-apple rust. Full profile | Kind: Rust fungi that need two hosts Hosts: The Morton Arboretum says the fungi spend part of their life on eastern red cedar and other junipers and part on apple, hawthorn and other members of the rose family, and that both hosts are needed to complete the life cycle. It says spores made on the rose-family host only infect juniper, and those from the evergreen host only infect rose-family plants. It describes the rust as spending one full year on junipers. Where and status: Eastern red cedar is the juniper named. No regulated status is given. Season: The Arboretum says that in the second spring, around crabapple bloom, rain-soaked galls swell and produce jelly-like spore horns, with spores dispersing mainly within several hundred feet but up to 5 miles. |
| Arborvitae leafminer, Argyresthia thuiella | Kind: Moth whose larvae mine the foliage Hosts: Natural Resources Canada names eastern white-cedar as the main host. It says the foliage turns from pale yellow to brown and the shoots die as larvae mine the needles, and that severe attacks over several years can kill twigs and occasionally stems, though infested trees can usually renew their foliage later in the growing season. Where and status: Natural Resources Canada lists British Columbia, Manitoba, New Brunswick, Ontario, Prince Edward Island and Quebec. It says it was first reported in Connecticut in 1921, first recorded in Canada in 1940 in Ontario, and that an infestation in Quebec from 1967 to 1973 killed a large number of stems. No regulated status is given. Season: Larvae overwinter and resume feeding in spring, and adults emerge between late May and late June. |
How the sources describe the effects
Forest Research calls Phytophthora lateralis aggressive. The Morton Arboretum says repeated cedar-apple rust infections can seriously weaken susceptible plants. For the leafminer, Natural Resources Canada describes salvage cuttings in southern Quebec stands after the 1967 to 1973 infestation.
Who the sources say to report to
Forest Research gives a report-a-sighting section for Phytophthora lateralis because it is notifiable in the plant trade in the United Kingdom. The pages read for the cedar rusts and the leafminer name no report line. The offices for each country are on the report a pest in the United Kingdom and report a pest in Canada pages.