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Japanese Maple Disease Problem - What To Do?

I recently had the following exchange with one of the newsletter subscribers. I think it illustrates how microscopic soil diseases and other pathogens can take advantage of opportunities to enter damaged tree roots. I really wasn't able to offer him much encouragement about the situation, but I'll be happy to pass along helpful suggestions from any of you.

To: Don Chapman
Subject: Verticillium Wilt

We have purchased a variety of products from you over the years for use with seeds or transplanting a wide variety of plants and receive your email newsletters.

A very serious problem has arisen with one of our old mature Japanese maples (25' x 20'). The almost certain diagnosis is verticillium wilt. There are several organism-specific biofungicides on the market and there is, of course, your own endo- and ecto-mycorrhizal products. I am wondering if you might have any experience in dealing with such problems in maples or can offer advice on the usefulness of drenching the area around this large, mature tree.


Hello Arvid -

My view is that the mycorrhizal fungi have been proven capable of preventing many diseases and warding off soil pathogens, partly by creating a better nourished tree and partly by directly blocking some problem organisms, but I doubt that putting our inoculant around the roots of an older tree would do any good after a disease is present. I have heard of some success with mature problem oaks by removing grass or other plants from underneath their drip area, putting down a coarse mulch, and then allowing the soil to dry out completely between waterings. The oak can survive extended droughts, but the soil pathogens cannot. Not sure if that applies to your maple??? Does it maybe receive too much watering?

Sorry I can't be more helpful.

Best regards,
Don Chapman

Hi Don --

Thank you for your response. Our troubled Japanese maple has occasionally irrigated lawn within six feet of the trunk on one side, every-other-day irrigation twelve to fourteen feet from the trunk on another and no irrigation on the other 150 degrees. I re-sodded the non-irrigated section last fall in preparation for our daughter's wedding last fall and kept that area drenched for several weeks. Before re-sodding I had to remove the old sod and in the process noticed that the maple had a dense root system right on the surface just underneath the sod. Needless to say, the roots were scuffed up during this process. If I'd had my wits about me I should have inoculated the scuffed areas prior to laying down the new sod. This is the only stress that this tree has had and is coincident with the winter die-back.

I will use up our remaining innoculant -- however old it may be -- on the surrounding lawn and reduce irrigation to a bare minimum. Anything further that I try or learn I will write to you about.

I don't mean to involve you unnecessarily in this problem, but having read so many of your newsletters, you may just have a passing interest.

Arvid ----------------------------------------------------------------------------------------------

Hi Arvid -

I think you've figured out the cause of the problem. Some trees are much more sensitive than others when it comes to disturbing their roots. Then, after the roots were scuffed, keeping the soil soaked for a long time allowed the disease organisms to multiply and enter the unprotected root openings. These diseases are always present in soil, but normally a tree and the mycorrhizal fungi are able to keep them outside the roots. Letting the soil go dry between waterings also keeps the disease populations low. Unfortunately, at this point the disease is systemic and I don't think that there is much that can be done beyond cutting back the dead parts of the tree and hoping that it will recover and re-grow.

Good luck with it,

Don Chapman

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