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Phytophthora on a Red/Silver Maple Hybrid #780310

Asked January 16, 2022, 11:52 AM EST

We have a previously very healthy hybrid maple (Acer saccharinum x rubrum) that appears to have developed a black weep and crack on the trunk. We planted it in 2009 as a balled and burlaped nursery stock tree, and it has thrived until a year ago. (The trunk went from 2" diameter to about 15" diameter in 12 years.) The weep developed after we had a professional pruning a little over a year ago. From what I can find on the internet (photos), it appears to be phytophthora fungal infection. Is it possible to restore the tree's health, or will the rot result in a potentially structurally unsafe tree over time? What should we look for in an arborist? I know you probably cannot point us to specific companies, but if you can give us a tip, that'd be really helpful. Mat Martinson<personal data hidden>)

Multnomah County Oregon

Expert Response

Hello, argh, that doesn't look good.  But it may not be the end of the tree or anything.  Phytophthora is probably a pretty good guess, but there are several other possibilities.  Here is a link to the PNW Plant Disease Management Handbook re: maple and Phytophthora diseases:  https://pnwhandbooks.org/plantdisease/host-disease/maple-acer-spp-phytophthora-root-rot

This includes both cultural and chemical solutions, although chemical methods are generally protectants, there are phosphonate fungicides which appear to slow the phyphthora down.

First you may want to look at the drainage situation around the tree, does it appear compacted and perhaps there is standing water a lot of the time?  This can facilitate Phytophthora.  Is there any way to improve the drainage issue if you think it may be a problem?

Regarding arborists, you may want to try a "consulting arborist", one that can do diagnosis and recommend treatments, but won't be the one to do the treatments, so is not likely to recommend things that aren't absolutely needed.

Here is the PNW ISA (International Society of Arboriculture) website with a "find an arborist" page, with a directory.

https://online.flippingbook.com/view/871593/

In the directory, the arborists will note whether they are consulting arborists or not.

I hope this helps.

An Ask Extension Expert Replied January 17, 2022, 2:27 PM EST

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