{"id":2766,"date":"2019-05-18T00:04:54","date_gmt":"2019-05-18T07:04:54","guid":{"rendered":"https:\/\/depts.washington.edu\/hortlib\/pal\/pal-question-559\/"},"modified":"2024-01-31T11:31:19","modified_gmt":"2024-01-31T19:31:19","slug":"diseases-affecting-english-laurels","status":"publish","type":"pal","link":"https:\/\/depts.washington.edu\/hortlib\/pal\/diseases-affecting-english-laurels\/","title":{"rendered":"diseases affecting English laurels"},"content":{"rendered":"<p><strong>I have some laurel bushes that are developing black or<\/strong><br \/>\n<strong>dark brown leaves. It starts at the top and then works down.<\/strong><br \/>\n<strong>Trimming them off seems to help but then another bush develops the<\/strong><br \/>\n<strong>problem. I want to take care of this before it gets out of control.<\/strong><br \/>\n<strong>A neighbor had an entire laurel die&#8211;it was probably 15 feet tall.<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>While I cannot diagnose a plant problem via e-mail,<br \/>\nit might be a bacterial or fungal problem, or an environmental<br \/>\ndisorder. I am assuming your laurels are English laurels (<em>Prunus<br \/>\nlaurocerasus<\/em>), not Mountain laurels (<em>Kalmia<\/em>). According to the<br \/>\n<a href=\"https:\/\/pnwhandbooks.org\/plantdisease\/host-disease\/prunus-laurocerasus-leaf-spots-shothole\">Oregon State University Extension&#8217;s Plant Disease database<\/a>, English<br \/>\nlaurel can suffer from leaf spots and shothole. Excerpt:<\/p>\n<blockquote>\n<p>Cause: Shothole symptoms are commonly observed on Prunus sp. and<br \/>\ncan be caused by a variety of factors. The bacterium Pseudomonas<br \/>\nsyringae pv. syringae and several fungi including Cercospora sp.,<br \/>\nBlumeriella sp., and Wilsonomyces carpophilum (Coryneum blight) can<br \/>\ncause leaf spots and shothole on cherry laurel (English laurel,<br \/>\nOtto Luyken, or &#8216;Zabeliana&#8217;). Copper spray injury and boron<br \/>\ntoxicity can also cause leaf spotting and shothole. When symptoms<br \/>\nare advanced, it is not possible to identify the cause<br \/>\nspecifically.<\/p>\n<p>Cherry laurels (English laurel, Otto Luyken, or &#8216;Zabeliana&#8217;), P.<br \/>\nlaurocerasus and sometimes other Prunus sp. including cherry and<br \/>\nplum, commonly show shothole symptoms resulting from cultural or<br \/>\nenvironmental stress. Research has failed to identify what specific<br \/>\nstress is responsible. Both container- and field-grown laurel can<br \/>\ndevelop symptoms.<\/p>\n<p>Symptoms: Necrotic leaf spots with circular to irregular margins.<br \/>\nBacterial spots are brown surrounded by a reddish border with a<br \/>\nyellow halo. Abscission layers develop around necrotic leaf spots<br \/>\ncausing the injured tissue to drop away, leaving holes and tattered<br \/>\nareas in the leaf (as if someone fired a shotgun at the leaf-thus<br \/>\nthe name shothole). After tissues drop, most often it is difficult<br \/>\nto determine specifically what caused the initial injury.<br \/>\nObservations of early symptom development, signs, and symptoms on<br \/>\nother areas of the plant may help make an accurate diagnosis. Note the holes in the leaves.<\/p>\n<p>Cultural control: No management practices have been shown to help<br \/>\nreduce physiological shothole. For disease-induced shothole, try<br \/>\nthe following cultural practices.<\/p>\n<ul>\n<li>Avoid overhead irrigation.<\/li>\n<li>Remove and destroy fallen leaves.<\/li>\n<li>Do not plant near other flowering or fruiting Prunus sp.<\/li>\n<\/ul>\n<\/blockquote>\n<p>If the problem is <a href=\"http:\/\/www.ipm.ucdavis.edu\/PMG\/GARDEN\/ENVIRON\/physiolshothole.html \">shothole,<\/a> this is usually an environmental<br \/>\ndisorder, and infected parts of the plant should be removed and<br \/>\ndestroyed.<\/p>\n<p><a href=\"http:\/\/www.ipm.ucdavis.edu\/PMG\/GARDEN\/PLANTS\/DISEASES\/baclfblight.html \">Here<\/a> is more information from U.C. Davis Integrated Pest Management on bacterial blight, which in laurels<br \/>\nusually affects only the leaves.<\/p>\n<p>If you want to be sure of what the problem is, I suggest<br \/>\nbringing samples of the affected leaves to one of the Master<br \/>\nGardener Clinics in our area.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I have some laurel bushes that are developing black or dark brown leaves. It starts at the top and then works down. Trimming them off seems to help but then another bush develops the problem. I want to take care of this before it gets out of control. A neighbor had an entire laurel die&#8211;it was probably 15 feet tall. &nbsp; While I cannot diagnose a plant problem via e-mail, it might be a bacterial or fungal problem, or an&#8230;<\/p>\n<div><a class=\"more-link\" href=\"https:\/\/depts.washington.edu\/hortlib\/pal\/diseases-affecting-english-laurels\/\">Continue reading <span class=\"screen-reader-text\">diseases affecting English laurels<\/span><\/a><\/div>\n","protected":false},"author":4,"featured_media":0,"menu_order":0,"template":"","keyword":[646,63,695],"class_list":["post-2766","pal","type-pal","status-publish","hentry","keyword-bacterial-diseases-of-plants","keyword-fungal-diseases-of-plants","keyword-prunus-laurocerasus"],"acf":[],"_links":{"self":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/pal\/2766"}],"collection":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/pal"}],"about":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/types\/pal"}],"author":[{"embeddable":true,"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/users\/4"}],"wp:attachment":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/media?parent=2766"}],"wp:term":[{"taxonomy":"keyword","embeddable":true,"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/keyword?post=2766"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}