White mildew-like spots on thornless Hawthorns - Ask Extension
We have white spot covering the trunk, large branches and at the nodes of small branches of all of our thornless hawthorn trees. At the nodes the whit...
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White mildew-like spots on thornless Hawthorns #778290
Asked November 23, 2021, 3:57 PM EST
We have white spot covering the trunk, large branches and at the nodes of small branches of all of our thornless hawthorn trees. At the nodes the white crud builds up to nearly pea-size. It looks only vaguely similar to images of powdery mildew online. Can you tell us what this is and how best to treat it? Three images (trunk, large branch and small branch node) uploaded. Thank you.
Boulder County Colorado
Expert Response
From the pictures at this point I would agree with you concerning the powdery mildew esp. considering our cool nights and warm days.
However, please check something first. The nodules on the branches..with a clean scraper..scrape off one of the nodules. If the nodules comes off fairly cleanly, look at the branch. If the branch is still "powdery" I would agree with the powdery mildew and have attached an information sheet on this.
If the node is hard or soft but one piece, look at the branch and see if a sticky or area of adhesion is left behind. It will look rather like a tiny snail had glued themselves into place. If this is the case this might be scale, but I'm not convinced. I have also attached a worksheet on this.
Either way best practice is to clean up and trash-so as not to spread-the leaves, berries,etc. under the tree. Do not fertilize as the tree is stressed right now. Control the -mildew I'm thinking- and water this winter at the base of the tree. Check you irrigation to be sure the spray is toward the base and not into the tree. Don't worry about any leaves already cycled into the compost outside of your yard. If you used the leaves in your yard, i recommend removing as much as possible.
Powdery mildew is fairly specific and shouldn't transfer to say-the pumpkin patch. The current weather bouncing back and forth between warm and cold, along with a bit of moisture is contributing to the mildew. These trees are pretty tough and should come back once treated. Be sure to check neighboring trees also.
I hope this helps. If you have further concerns, please text.
Boulder co mg
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Sent: Wednesday, November 24, 2021 2:54 PM
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Subject: [EXTERNAL] Question assigned to you (#0048221)
Sent: Wednesday, November 24, 2021 2:54 PM
To: Boulder County Parks Master Gardeners <<personal data hidden>>
Subject: [EXTERNAL] Question assigned to you (#0048221)
Hi Boulder County,
Question #0048221 has been assigned to you by CSU E.
White mildew-like spots on thornless Hawthorns
We have white spot covering the trunk, large branches and at the nodes of small branches of all of our thornless hawthorn trees. At the nodes the white crud builds up to nearly pea-size. It looks only vaguely similar to images of powdery mildew online. Can you tell us what this is and how best to treat it? Three images (trunk, large branch and small branch node) uploaded. Thank you.
From: James Snedeker
Submitted: 11/23/2021 3:57 PM
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