Sudden Oak Death hitting South Coast forests

Discolored leaves show signs of Sudden Oak Death Syndrome on trees near Humbug State Park

A silent killer is taking its' toll on Oregon forests.

The South Coast was again hit by the spread of Sudden Oak Death in 2023. So far, more than 40 tanoak trees near Humbug State Park area have tested positive for the fungal-like pathogen that causes Sudden Oak Death.

The invasive disease has already killed hundreds of thousands of tanoaks in Oregon, and many more are suspected to be infected.

The pathogen Phytophthora ramorum causes Sudden Oak Death, and is present in a number of Oregon nurseries. Curry County is the only region of the state where the pathogen is found in natural settings.

According to the Oregon Department of Agriculture, it is believed that the pathogen was introduced into the area through infected nursery plants. Areas of Curry County are under a partial quarantine and growers of host plant material are subject to quarantine restrictions.

Forest agencies have been keeping a close eye on trees found in and around infected areas.

Gabriela Ritokova is a forest pathologist with the Oregon Department of Forestry who has been monitoring areas in Oregon that have been infected with Sudden Oak Death.

“It kills highly susceptible trees in the Oak family, most notably tanoaks, but also California black oak and canyon live oak, by causing cankers on the main stem that girdle the trunks of the trees,” Ritokova stated.

This 'sudden' death appears to happen very quickly, although the tree may actually have been infected for several months.

So far the Sudden Oak Death pathogen has killed more than 1 million oak and tanoak trees in 15 coastal counties in California and thousands of tanoaks in Curry County, Oregon.

The new site in Oregon where Sudden Oak Death was found is approximately 1.5 miles south of the existing emergency quarantine boundary around Port Orford.

Ritokova suspects the latest infestation near Humbug State Park spread from the infestation in Port Orford. Wind can carry the spores across the landscape as far as 3 to 5 miles per year, she said.

Although the infected trees are not within the popular Humbug State Park campground, day-use area, or most hiking trails. Oregon Parks and Recreation Department is advising hikers to stay on trails between now and December as efforts to eradicate the pathogen at the site take place.

This site marks the third confirmation of Sudden Oak Death to the north of the 515-square mile quarantined portion of Curry County since March 2021.

Ritokova said Sudden Oak Death spreads during rainy periods. Spores from infected areas wash down onto nearby tree trunks or on top of vegetation growing on the forest floor. It can also be released in foggy conditions when spores on infected tanoak leaves and twigs are released into the air.

People can also spread spores if they move plants that have been infected, carry firewood from an infected tree or track soil from the area.

The disease can infect many different types of plants. The tanoak is the most notable, but SOD can also cause damage and blight in native rhododendron, evergreen huckleberry, Douglas-fir, grand fir and Oregon myrtle.

In Oregon, these other hosts are only infected when they grow in close proximity to infected tanoaks.

The Oregon Department of Forestry and US Forest Service direct disease mitigation efforts within the infested areas of Southwestern Oregon.

The disease negatively impacts forest ecology and could create economic problems if it spreads into forest products sold in International markets. International forest product markets are not open to diseased plant material.

Public engagement is encouraged to reduce the spread of Sudden Oak Death in Southern Oregon.

Residents are asked to learn the location of the quarantine area and not to move plant material or soil from infected areas, as well as to report any dead or dying tanoak and suspicious symptoms and their location to the Oregon Department of Forestry Sudden Oak Death program manager Randy Wiese at (541) 294-8425.

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