In tanoaks, the disease is recognized by wilting new shoots, older leaves becoming pale green, and after a period of two to three weeks, foliage turning brown while clinging to the branches.

Ambrosia beetles (Monarthrum scutellare) will most likely infest a dying tree during midsummer, producing piles of fine white dust near tiny holes.

), coast redwood (Sequoia sempervirens), Douglas fir (Pseudotsuga menziesii), coffeeberry (Rhamnus californica), honeysuckle (Lonicera hispidula), and Shreve oak (Quercus parvula).

[8] In 2009, the pathogen was found to be infecting and killing large numbers of Japanese larch trees (Larix kaempferi) in the United Kingdom at sites in the English counties of Somerset, Devon, and Cornwall.

[18] These spores are then carried by rain and air currents to the leaves of the new bole canker host, which include broadleaf trees like tanoaks, where they begin to develop.

P. ramorum is spread by air;[20] one of the major mechanisms of dispersal is rainwater splashing spores onto other susceptible plants, and into watercourses to be carried for greater distances.

[29] It is currently not clear whether this pathogen can reproduce sexually in nature and genetic work has suggested that the lineages of the two mating types might be isolated reproductively or geographically given the evolutionary divergence observed.

Plugs of tomato juice agarose containing actively growing P. ramorum cultures of different types on carrot agar and incubated in the dark at 20 Celsius.

[citation needed] In 2021, research came out revealing that the origins of this pathogen are subtropical laurisilva forests in East Asia, specifically the area near the border of Vietnam and Yunnan, China, as well as southwestern Japan.

[33] P. ramorum is an introduced species, and these introductions occurred separately for the European and North American populations, hence why only one mating type exists on each continent – this is called a founder effect.

Similar impact applies to the decline of other native plant species that are traditional food sources in tanoak and oak regimens infected by the pathogen.

Bee hives situated in areas of heavy Agrifos spraying have incurred significant losses of population in direct correlation to the application of these chemicals.

Such damage to the pollinator populations may have tertiary negative effects on the entire local plant community, compounding the loss of biodiversity, and thus environmental value, attributable to SOD.

[44] Another significant environmental impact of P. ramorum is its tendency to result in large deposits of dry, woody debris in areas prone to forest fires, making them even more difficult to contain.

On the landscape level, P. ramorum's fast and often undetectable movement means that any treatment hoping to slow its spread must happen very early in the development of an infestation.

Host material is removed from the leading edge of a plant tissue canker caused by the pathogen; resulting growth is examined under a microscope to confirm the unique morphology of P. ramorum.

[51] As part of a nationwide USDA program, a ground-based detection survey was implemented from 2003 to 2006 in 39 U.S. states to determine whether the pathogen was established outside the West Coast areas already known to be infested.

[52] Aerial surveying has proven useful for detection of P. ramorum infestations across large landscapes, although it is not as "early" a technique as some others because it depends on spotting dead tanoak crowns from fixed-wing aircraft.

Sophisticated GPS and sketch-mapping technology enable spotters to mark the locations of dead trees so that ground crews can return to the area to sample from nearby vegetation.

Under conducive weather conditions, the zoospores are attracted to the baits and infect them, causing lesions that can be isolated to culture the pathogen or analyzed via PCR assay.

Of course, it cannot detect the exact locations of those infected plants: at the first sign of P. ramorum propagules in the stream, crews must scour the watershed using all available means to find symptomatic vegetation.

Since U.S. regulators in 2004 discovered that P. ramorum had spread nationwide to a number of hosts, proactive inspections of agricultural shipments have been shown to help reduce the risk of infestations of sudden oak death.

[56] Moreover, the USDA's APHIS specifically plans to stop the spread of SOD by continuing their public outreach program and by passing regulations on the transfer of agricultural products that might be a disease vector for P. ramorum.

[57] Therefore, a number of biosecurity measures must be taken to ensure that SOD is not unintentionally transferred to one's nursery, including driving vehicles only on paved, concrete, or gravel areas at inspection sites in order avoid contact with soil organic matter that could pose as a potential disease vector.

[58][59][60] The eradication campaign involves vigorous early detection by airplane and watercourse monitoring, a U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) and Oregon Department of Agriculture-led quarantine to prevent movement of host materials out of the area where infected trees are found, and immediate removal of P. ramorum host vegetation, symptomatic or not, within a 300-foot (91 m) buffer around each infected tree.

For one thing, the organism was too well established in forests in the Santa Cruz and San Francisco Bay areas by the time the cause of sudden oak death was discovered to enable any eradication effort to succeed.

An initially promising treatment for preventing infection of individual oak and tanoak trees—not for curing an already established infection—is a phosphonate fungicide marketed under the trade name Agri-fos.

Phosphonate is a neutralized form of phosphorous acid that works not by direct antagonism of Phytophthora, but by stimulating various kinds of immune responses on the part of the tree.

[63] Another area of research and evolving practice deals with eliminating P. ramorum from nursery environments in which it is established to prevent human-mediated pathogen movement within the ornamental plant trade.

In 2023 the Forestry Commission issued a Statutory Plant Health Notice to Sheffield and Rotherham Wildlife Trust ordering it to remove over 1,000 trees at their nature reserve at Wyming Brook.