{"id":12486,"date":"2019-05-30T16:21:57","date_gmt":"2019-05-30T16:21:57","guid":{"rendered":"https:\/\/www.purdue.edu\/fnr\/extension\/?p=12486"},"modified":"2025-07-30T14:36:32","modified_gmt":"2025-07-30T18:36:32","slug":"special-alert-sudden-oak-death","status":"publish","type":"post","link":"https:\/\/www.purdue.edu\/fnr\/extension\/special-alert-sudden-oak-death\/","title":{"rendered":"**SPECIAL ALERT** Sudden Oak Death"},"content":{"rendered":"

\"Dying<\/a>Sudden oak death, as the name suggests, is a disease that is capable of rapidly killing certain species of oaks.\u00a0 It was first identified in California, in 1995. Two years earlier it was identified in Germany and the Netherlands, killing rhododendron. Because the pathogen originally infected and killed tanoaks, an undesirable, understory scrub tree, it generated little interest until other, more desirable oaks species began dying.\u00a0 However, by this point, the disease was well established and eradication no longer an option, with millions of oak trees killed by the disease.\u00a0 Currently, over 120 hosts in addition to oaks have been identified, and more continue to be added to this list.\u00a0 What is most unusual about sudden oak death is the severity of disease symptoms coupled with the broad host range of the pathogen. This leads to difficulty in diagnosing and managing this disease.<\/p>\n

What causes this disease?
\n<\/strong>The pathogen that causes SOD is Phytophthora ramorum<\/em> (pronounced F\u012b-toff-thor-\u0103\u00a0 r\u0103-mor-\u01d4m).\u00a0 This pathogen belongs to a group of organisms in the Kingdom Chromista, and has characteristics similar to fungi, plants and animals.\u00a0 It spreads throughout the plant by hyphal threads (like fungi), produces spores (like fungi) that have flagella and swim through water (like animals), but its cell wall is made up of cellulose (like plants). When conditions dry up, Phytophthora can produce thick walled sexual spores called oospores, or asexual chlamydospores. Because P. ramorum<\/em> is not a \u2018true\u2019 fungus, many fungicides labeled for control of other fungal diseases are not effective against it.<\/p>\n

With such a broad range of plant hosts, it is important to stress that P. ramorum<\/em>\u00a0affects different species in different ways. Identification must be confirmed in the laboratory and cannot be identified on field symptoms alone. Many common landscape shrubs are also infected by other endemic Phytophthora species, and symptoms look similar. Boring insects and other root rots may be mistaken for this disease. For this reason, all Phytophthora infections should be screened by the Purdue Plant and Pest Diagnostic Laboratory<\/a>.<\/p>\n

What are the symptoms of SOD?
\n<\/strong>To understand this disease, it is important to recognize that there are two categories of hosts: bark canker hosts and foliar hosts. Further complicating this is the fact that oaks are divided into three subgroups, and only the red oak group are susceptible to this pathogen. Of our 17 oak species in Indiana, half are potentially, or known to be susceptible, and include black, blackjack, cherrybark, Northern pin, pin, red, scarlet, and Shumard oaks. Diagnostic symptoms of infected red oaks include oozing sap and red-brown cankers that often leading to death.<\/p>\n

Our concern right now is on \u2018the other\u2019 hosts. Despite its name, sudden oak death primarily spreads through foliar hosts that are sold throughout the United States. Foliar hosts include rhododendrons, azalea, viburnum, lilac, and periwinkle (Vinca minor)<\/em>.<\/p>\n

These hosts (and many others) are infected via the leaves and small branches. These infections rarely cause death, and can be mistaken for sunscald, twig canker, and dieback caused by other pathogens, including native Phytophthora species. Although symptoms from these infections are not severe, and are rarely fatal, the infections produce enormous numbers of spores that can infect neighboring, susceptible oaks\u2014and other plant species. For this reason, we are asking people to examine any rhododendrons (or other co-mingled hosts like azalea, viburnum and lilac) purchased this spring from Walmart and Rural King, while the disease may still be controlled and the pathogen contained. Although this disease doesn\u2019t look like much on rhododendron or lilac, its ability to spread to oaks and kill them is what makes it so devastating. These shrubs play a key role in the spread of P. ramorum<\/em>, acting as a breeding ground for spores (inoculum) that can spread through water, wind-driven rain, plant material, or human activity. Oaks are considered terminal hosts, since the pathogen does not readily spread from intact bark cankers; they become infected only when exposed to spores produced on the leaves and twigs of neighboring plants.<\/p>\n

For full article and photos view: Purdue Landscape Report<\/a><\/p>\n

Other resources:<\/strong>
\nSudden Oak Death<\/a>, California Oak Mortality Task Force
\nSudden Oak Death<\/a>, Indiana Department of Natural Resources
\nWhite Oak<\/a>, The Education Store, Purdue Extension resource center
\nPlanting Forest Trees and Shrubs in Indiana<\/a>, The Education Store
\nSuccessful Oak and Hickory Regeneration<\/a>, The Hardwood Ecosystem Experiment: 2006-2016, The Education Store
\nFind a Certified Arborist<\/a>, International Society of Arboriculture<\/p>\n

Janna Beckerman<\/a>, Professor
\nPurdue Botany and Plant Pathology<\/p>\n","protected":false},"excerpt":{"rendered":"

Sudden oak death, as the name suggests, is a disease that is capable of rapidly killing certain species of oaks.\u00a0 It was first identified in California, in 1995. Two years earlier it was identified in Germany and the Netherlands, killing rhododendron. Because the pathogen originally infected and killed tanoaks, an undesirable, understory scrub tree, it […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[38,870,42,80,49,53],"tags":[488,817,916,918,917,262],"class_list":["post-12486","post","type-post","status-publish","format-standard","hentry","category-alert","category-disease","category-forestry","category-trees","category-plants","category-urbanforestry","tag-disease","tag-landscape-report","tag-oak-death","tag-phytophthora-ramorium","tag-rhododendron","tag-tree"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts\/12486","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/comments?post=12486"}],"version-history":[{"count":15,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts\/12486\/revisions"}],"predecessor-version":[{"id":33807,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts\/12486\/revisions\/33807"}],"wp:attachment":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/media?parent=12486"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/categories?post=12486"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/tags?post=12486"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}