fungus or mold in ground under Japanese maple

Asked October 28, 2019, 5:43 PM EDT

Hi, While cleaning up under some Japanese maples for the coming winter I encountered in a few spots a scattered and thin layer of white substance about 1/2 to 1 inch below the surface. It appears to be some type of mold, but might be a fungus. I used a flat shovel and scraped off the top 1 to 1.5 inches of soil and intend to replace it with an acid-loving planting mix such as either Gardner & Bloome Organics acid planting mix [from the Grange] or Master Nursery Bumper Crop natural organic soil builder [from a local nursery where I have been buying maples]. My question: should I first treat the soil under the tree with a fungicide before placing the layer of either of the above? Will the fungicide hurt or help the Japanese maple? I ask because I lost a beautiful Japanese maple 3 years ago, we think due to fungus in the soil. Following that, I removed that soil down 2 feet and across 8-9 feet under where that tree died and treated the hole [bottom and side walls with a fungicide [ferti-lome Consan 20]. Early this summer I planted another maple in that same spot [this is not the one where I recently encountered the mold or fungus, which led to this email]. Your thoughts? Thanks, Tom

Jackson County Oregon trees and shrubs fungi

3 Responses

You may have a problem with phytopthora, a root fungus. Avoid ponding of water around plants. Avoid over- or under-watering plants. Plant in a well-drained area. Remove and destroy all infected plants and plant debris. Prevent mechanical injury to trees, especially late in the season. Do not let sprinkler irrigation wet landscape tree trunks.

Here are some publications that may be useful:

If your tree does not appear to show any symptoms of root rot, and appears to be healthy, then cover the bare ground with compost.

Hope this helps!

Looks like I lost what I was writing when I went back to one of the links you posted. Assuming this response posting process allowed that to get to you, I wanted to add that we live at about 2450 ft elevation on a hillside above Ashland [within the city limits]. Our soil is mostly DG and drains quite well. About 30 years ago right after the house was built a layer of bark dust was brought in to control weeds [after killing and removing weeds, especially poison oak. Over the last 10-12 years I've planted 4 Japanese maples in the general area of concern, and only lost the one tree 3 years ago.
Earlier this year when I dug out [down 2 feet and 8 to 9 feet across] what I feared was contaminated soil where a tree died 3 years ago I treated the hole with "Consan 20" as mentioned in my 1st email seeking help. The 2nd link you sent [pnwhandbooks,org] says that I may need to alternate different fungicides to avoid the fungus [if it is the bad fungus] from developing an immunity to just one type of fungicide.

How important is this [alternating different fungicides] and what would you recommend besides the "Consan 20"?
I suspect I won't know if what I have already done has been effective until next spring when the maples leaf out.

Even if there is no obvious problem next spring, I'm temped to apply a fungiside to try to control any bad fungus.
The lady at the Grange suggested I apply a seaweed solution [Ohrstrom's Maxicrop liquid seaweed 0-0-1] now to help the tree root this winter and in the spring. Her concern is that if the fungus I encountered is just normal wood decomposition, applying a fungicide could harm the tree roots that rely on normal non-pathogenic fungus in the soil for acquiring nutrients. At least, that's what I think she said.
Your thoughts?
Oh, I forgot to mention that before the maple died 3 years ago [had been in the ground and healthy for about 3 years] a quaking aspen ["QA"] had died because of having been "buck-rubbed" [removing about 70% of the bark around -- almost girdling the tree]. I dug out the root mass from that dead QA, before planting the maple that eventually died in the same spot [we joked about it being bad karma]. Is there anything about decomposing QA roots [that I failed to completely dig out] that might be a problem?

Sorry for so many questions.


One of the links sent describes many beneficial fungi. This is more likely what you are seeing.

I would recommend that you refrain from applying fungicides to your trees and soil until you know you actually have a problem. Why do you think your soil is contaminated?

Do you see damage to your trees? Wilting foliage? Cankers on the tree trunk or branches? Stunted growth? If not, you can just apply compost and mulch and keep your tree hydrated during the dry periods.

Hope this helps!