{"id":374,"date":"2017-10-03T06:15:52","date_gmt":"2017-10-03T06:15:52","guid":{"rendered":"http:\/\/blogs.oregonstate.edu\/mgmetro\/?p=374"},"modified":"2017-12-27T07:11:22","modified_gmt":"2017-12-27T07:11:22","slug":"pear-trellis-rust-new-disease","status":"publish","type":"post","link":"https:\/\/blogs.oregonstate.edu\/mgmetro\/2017\/10\/03\/pear-trellis-rust-new-disease\/","title":{"rendered":"Pear Trellis Rust – A New Disease"},"content":{"rendered":"

Natter\u2019s Notes:
\n<\/strong>Pear Trellis Rust, a new disease<\/strong><\/h1>\n

Jean R. Natter, OSU Master Gardener
\n<\/strong><\/h3>\n

Recently, Pear Trellis Rust (Gymnosporangium sabinae<\/em>) became the newest contributor to this hodge-podge-let\u2019s-try-everything year. During 2016, the first case of pear trellis rust was reported in the northern section of the Willamette Valley, that on a Bartlett pear growing in Milwaukie, Clackamas County. (See \u201cPear Trellis Rust: First Report in Oregon\u201d Metro MG Newsletter, January 2016;\u00a0 http:\/\/extension.oregonstate.edu\/mg\/metro\/sites\/default\/files\/dec_2016_mg_newsletter_12116.pdf<\/a>). Then, in mid-September 2017, an inquiry about a pear leaf problem in Multnomah County was submitted to Ask an Expert. [Fig 1; Fig 2] Yes, it\u2019s another fruiting pear tree infected with trellis rust. It seems that gardeners are beginning to recognize this newcomer.<\/p>\n

\u201cSymptoms [of trellis rust] on pear begin as yellowish-orange leaf spots early in the season. Young fruit and twigs can also be infected. Leaf spots can become bright reddish orange during the summer. By mid-summer, tiny black dots (pycnia) appear in the center of the leaf spots.\u201d [Fig 3] By late summer, brown, blister-like swellings form on the lower leaf surface just beneath the leaf spots. This is followed by the development of acorn-shaped structures (aecia) with open, trellis-like sides that give this disease its common name. (Fig 4) Aeciospores produced within the aecia are wind-blown to susceptible juniper hosts where they can cause infections on young shoots. These spores are released from late summer until leaf drop.\u201d (\u201cPear Trellis Rust, Gymnosporangium sabinae<\/em>\u201d (http:\/\/www.ladybug.uconn.edu\/FactSheets\/pear-trellis-rust_6_2329861430.pdf<\/a>)<\/p>\n

Signs on affected alternate host junipers are difficult to detect. During wet weather in spring, look for swollen areas on branches which exude orange jelly-like horns.<\/p>\n

Differentiate Trellis Rust from Pacific Coast Pear Rust <\/strong><\/p>\n

Trellis Rust is quite different from the widespread Pacific Coast Pear Rust you\u2019ve likely seen every spring on Amelanchier<\/em> (shadbush; serviceberry) and pears.<\/p>\n

Pacific Coast Pear Rust infects both Asian and European pears.\u00a0 And, as is common with rusts, it also has an alternate host. During spring, host incense cedars (Calocedrus decurrens<\/em>) are recognized by the bright orange jelly-like globs on the foliage. On pears, the bright orange, powdery spores erupt on fruits, flowers, leaves, and twigs, often deforming them. [Fig 5; Fig 6] Management includes removing nearby hosts. A home-use spray is available for ornamental pears but not edible pears. (Keep current with the PNW Disease Management Handbook.)<\/p>\n

Management strategies for trellis rust\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong><\/p>\n

Minimizing overhead irrigation might help reduce the number of infections. But you know how Oregon springs are.\u00a0 It rains! Cultural management may help decrease infection rates:<\/p>\n

    \n
  1. Collect and discard infected leaves.<\/li>\n
  2. If practical, remove juniper hosts from a 1000-ft radius. (The PNW Disease Handbook states \u201cJ. communis<\/em>, J. horizontalis<\/em>, and J. squamata<\/em> are immune or highly resistant.\u201d)<\/li>\n
  3. No chemical remedies are available for edible pears.<\/li>\n<\/ol>\n

    Master Gardeners as First Responders<\/strong><\/p>\n

    When MGs see a plant affected by a disease or insect, we\u2019re required to verify our tentative diagnosis before we suggest a remedy. So, here\u2019s an important project for you: Help track the spread of Pear Trellis Rust.<\/p>\n

    If you suspect pear trellis rust while volunteering at the MG Offices or elsewhere in the metro counties, request images and\/or samples. Take pictures and jot down a history with at least these few facts, if known: the name and age of the pear; when the client first detected the problem; also, in which town the tree grows. Next, email the images and history to me (j.r.natter@aol.com<\/a>). After I verify your tentative diagnosis, I will notify both you and the pathologist.<\/p>\n

    \n
    \n \"Image<\/a>\n
    Fig 1: Pear trellis rust (Gymnosporangium sabinae) on the top leaf surface of edible pear tree; Multnomah County, OR. (Client image; 2017-09)<\/figcaption>\n <\/figure>\n
    \n
    \n \"\"<\/a>\n
    Fig 2: Pear trellis rust (Gymnosporangium sabinae) on the reverse of a leaf from an edible pear tree; Multnomah County, OR. (Client image; 2017-09)<\/figcaption>\n <\/figure>\n
    \n
    \n \"Pear<\/a>\n
    Fig 3: Pycnia (the black dots) of pear trellis rust on the upper leaf surface are involved in development of infectious structures on the underside. Bartlett pear tree; Milwaukie, Clackamas County, OR. (R. Frick-Wright; 2017-09)<\/figcaption>\n <\/figure>\n

    Click the link below for a PDF containing the above text and all the images.<\/span><\/h4>\n

    Pear Trellis Rust PDF<\/a><\/h3>\n

     <\/p>\n

    \u00a0<\/span><\/h4>\n

     <\/p>\n","protected":false},"excerpt":{"rendered":"

    Natter\u2019s Notes: Pear Trellis Rust, a new disease Jean R. Natter, OSU Master Gardener Recently, Pear Trellis Rust (Gymnosporangium sabinae) became the newest contributor to this hodge-podge-let\u2019s-try-everything year. During 2016, the first case of pear trellis rust was reported in the northern section of the Willamette Valley, that on a Bartlett pear growing in Milwaukie,… Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":8248,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1179565],"tags":[],"class_list":["post-374","post","type-post","status-publish","format-standard","hentry","category-natters-notes"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/posts\/374","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/users\/8248"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/comments?post=374"}],"version-history":[{"count":9,"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/posts\/374\/revisions"}],"predecessor-version":[{"id":649,"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/posts\/374\/revisions\/649"}],"wp:attachment":[{"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/media?parent=374"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/categories?post=374"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/mgmetro\/wp-json\/wp\/v2\/tags?post=374"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}