Phytophthora lateralis: what the agencies record

This page reports what the official source says. It is not legal advice: ask the office named here. It lists what the sources record about Phytophthora lateralis and does not diagnose any tree. It describes a reporting rule for the plant trade in the United Kingdom, so the exact wording is on the page linked below. The list of other diseases is on the tree diseases page, and the reporting lines are in the United Kingdom report-a-pest guide. A related water mould is covered on the sudden oak death page.

At a glance

Item	What the sources say
Pathogen	Phytophthora lateralis, a water mould. Forest Research calls it a fungus-like pathogen. Oregon State Extension says water moulds are relatives of fungi that lack conspicuous fruiting structures.
Hosts	Forest Research says it mostly affects Lawson cypress (Chamaecyparis lawsoniana) and lists Sawara cypress, western red cedar, Pacific yew, northern white cedar, other cypress species and juniper. In its native range the host is called Port-Orford-cedar. Oregon State Extension says Pacific yew can also be infested and that Douglas-fir and western redcedar neighbours are not.
Where	Forest Research says all four countries of the United Kingdom, more prevalent in Scotland and Northern Ireland than in England and Wales, plus the Republic of Ireland, the Netherlands, Belgium, France, west-coast states of the USA and Taiwan. Don't Move Firewood says it was first reported near Seattle in 1923 and found in native Port-Orford-cedar in 1952.
Status in the United Kingdom	Present, and notifiable in the plant trade. Forest Research says there is no requirement to report suspected cases in the wider environment.
Report to	Trade premises: the plant health authority for the country. Public sites with several trees: TreeAlert in Great Britain or TreeCheck in Northern Ireland, as Forest Research asks. See the United Kingdom guide.

How the sources say it spreads

Forest Research says the disease spreads when tree roots meet spores in soil or water, that planting infected plants or using soil that carries spores are key ways it reaches new sites, and that once present, spores can travel in water run-off or on footwear and vehicles. It also describes genetic variants able to cause branch dieback through spread in water droplets in the air. Oregon State Extension says the pathogen is easily moved on muddy road-building machinery, maintenance equipment and shoes, that it passes from one tree to the next through joined roots, and that infestations often start at the edge of a road or driveway and move slowly into the forest. Don't Move Firewood adds that spores travel in surface water or splashing rain, mostly in wet spring weather, and that moving infected nursery stock, including other Chamaecyparis species, can spread it.

Symptoms as the sources state them

Foliage. Forest Research says foliage of infected Lawson cypress turns pale green, then dull bronze or rust red as the tree dies, and that isolated bronze or brown patches in the crown show the stem or branches are infected. The US Forest Service abstract says killed Port-Orford-cedars typically turn vivid reddish brown, which shows from the air.
Inner bark. Forest Research says the phloem becomes discoloured as infection rises from the roots and root collar, and that tongues of darker dead tissue show when the outer bark is removed. Oregon State Extension describes a characteristic stain on the cambium of a newly dead tree.
Speed. Forest Research says infected trees decline quickly and few recover. Don't Move Firewood says seedling death can come within days and that mature trees can take two to four years to die.

Look-alikes

Forest Research says the symptoms can be similar to those caused by Phytophthora cambivora or Armillaria species, which occur in the United Kingdom. Oregon State Extension says western redcedar and Port-Orford-cedar can look alike from a distance and describes cones, the pattern on the underside of foliage and bark as ways it says to tell them apart. It also says beetle galleries under loose bark on dead trees can come from beetles that invade already dead or dying trees.

What the agencies publish for control

Forest Research says statutory action by the plant health authority, usually destruction of infected and nearby susceptible plants, is exceptional, and that in most cases the owner or manager carries out the work voluntarily. It advises asking suppliers about nursery stock origin and biosecurity. Don't Move Firewood describes restricted movement of people and machinery in wet periods where spores are abundant, and a US Forest Service breeding programme that has screened over 9,000 trees for resistance. Oregon State Extension says the disease is difficult to treat, that fungicide treatment on a single notable tree needs continued repeats and is unlikely to be practical when many trees are infested, and that resistant seedlings are available. Who may apply pesticides is covered on the pesticide licences page.

Credit

The Forest Research material was read under the Open Government Licence v3.0 and is restated here in our own words. The US Forest Service page is a federal publication.