Leaves small and thinning on mature maple tree in masonary raised circle bed

Asked June 17, 2020, 5:06 PM EDT

We noticed this spring our previous healthy 15 year old maple tree branches are very small and thinning and haven’t grown out this summer. Some branches look Like they still have buds on them. Is this the start of verticillium wilt? Any cure besides cutting it down? Thank you, Sheila

Clark County Washington

1 Response

Yes, unfortunately it most likely is verticillium wilt. For now, prune out the branches if you want to enjoy the tree for a few more years. You can diagnose it for yourself when you prune affected branches: There is usually a characteristic staining in the affected branches. Take a look at this image. https://www.apsnet.org/edcenter/disandpath/fungalasco/pdlessons/Article%20Images/VerticilliumWilt06..... Normal branch appearance is on the left. The brown staining on the right is what you might--not always--see with branches affected by verticillium wilt.

One of the characteristics is loss of leaves and death of branches on just a part of the tree. This can progress until most of the limbs are denuded. Verticillium is a fungal disease that lives in the soil and attacks the tree's vascular system.
One more thing--if you decide to take the tree out at some time in the future, be sure to replace it with a shrub or tree that is resistant to verticillium wilt--remember, the pathogen lives in the soil and can infect other susceptible plants.

Here is a very good article from PNW Handbooks, with good images. Your care of the tree is going to be managing the problem, not curing it. https://pnwhandbooks.org/plantdisease/host-disease/maple-acer-spp-verticillium-wilt
Check out the article:

Prune off and burn affected limbs preferably before leaves fall and thus before new inoculum is incorporated into the ground.
Clean pruning equipment after use.
Do not track soil from infested areas into clean areas. Clean boots, equipment, and tools before leaving an infested area.
Keep nitrogenous fertilizers to a minimum-enough only to produce normal, not succulent, growth.
If the tree dies and/or is removed, replace it with a nonsusceptible host such as any conifer, birch, dogwood, or sycamore.
Avoid planting maple in fields with a history of Verticillium wilt. Avoid fields previously planted to potato or tomato; however, former peppermint fields may be lower risk.
A preplant soil test for Verticillium propagules will help determine a planting site.
Incorporating freshly mown Italian ryegrass followed by covering the soil with plastic for 3 months in the late summer was effective in the Netherlands at reducing disease incidence in a nursery crop of Norway maple planted 6 months later. Effect was observed up to 4 years after planting.