{"id":2665,"date":"2019-09-27T00:03:13","date_gmt":"2019-09-27T07:03:13","guid":{"rendered":"https:\/\/depts.washington.edu\/hortlib\/pal\/pal-question-333\/"},"modified":"2023-08-09T09:08:14","modified_gmt":"2023-08-09T16:08:14","slug":"common-pests-and-diseases-affecting-japanese-maples","status":"publish","type":"pal","link":"https:\/\/depts.washington.edu\/hortlib\/pal\/common-pests-and-diseases-affecting-japanese-maples\/","title":{"rendered":"common pests and diseases affecting Japanese maples"},"content":{"rendered":"

I have a lovely, 3-ft. Japanese Maple (Acer palmatum<\/i>) that has access to full sun. I am guessing it is over 3 years old at least. The tree is leafing beautifully, but last week I noticed there are “pustules” all over the stems and branches. They are yellowish-brown in color and somewhat mottled looking. They form in irregular clusters along the branch. Each pustule is about the size of a ladybug; in fact, at first I thought they were beetles, but they do not move and when I removed one, it was liquid-y inside and left a thin, white streak along the branch. I am a beginner homeowner, so I do not know what this is. Do you have any ideas? What can I do to treat this? I would hate to lose my Japanese Maple.<\/strong><\/p>\n

The best way to determine if your tree is diseased is to bring a sample to a Master Gardener Diagnostic Clinic<\/a> and ask a Master Gardener to diagnose it for you. This service is free to home gardeners.<\/p>\n

What you describe sounds like several quite different problems (canker, or scale, for instance), which is why having a hands-on diagnosis is so important. Below is general information about maple diseases which you can compare with your tree. Additionally, I recommend the book Japanese Maples<\/em> by J.D. Vertrees and Peter Gregory (Timber Press, 2009). It has sections on the most common pests and diseases affecting Japanese maples.<\/p>\n

This page from the University of California Agriculture and Resources about Maples<\/a> includes an extensive list of diseases and disorders that affect maple trees.<\/p>\n

Clemson State University has a factsheet on Maple diseases and insect pests<\/a> (read the entry on scale).<\/p>\n

Try searching for “maple” in Pacific Northwest Guide to Plant Disease Control<\/a>, and compare the descriptions to see if any ring true with what you are seeing. Ultimately, though, the best thing is to get a hands-on diagnosis from the Master Gardeners, as mentioned above.<\/p>\n","protected":false},"excerpt":{"rendered":"

I have a lovely, 3-ft. Japanese Maple (Acer palmatum) that has access to full sun. I am guessing it is over 3 years old at least. The tree is leafing beautifully, but last week I noticed there are “pustules” all over the stems and branches. They are yellowish-brown in color and somewhat mottled looking. They form in irregular clusters along the branch. Each pustule is about the size of a ladybug; in fact, at first I thought they were beetles,…<\/p>\n

Continue reading common pests and diseases affecting Japanese maples<\/span><\/a><\/div>\n","protected":false},"author":4,"featured_media":0,"menu_order":0,"template":"","keyword":[458,290],"class_list":["post-2665","pal","type-pal","status-publish","hentry","keyword-acer-palmatum","keyword-plant-diseases"],"acf":[],"_links":{"self":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/pal\/2665"}],"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=2665"}],"wp:term":[{"taxonomy":"keyword","embeddable":true,"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/keyword?post=2665"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}