Hello Joseph,

Most likely causes of bark scarring on a Japanese maple in Michigan include animal feeding (rabbits, voles, deer), canker diseases, or sunscald. Established Japanese maples generally need very little fertilizer—only apply a slow‑release product in spring if a soil test or poor growth indicates a deficiency.

Please read the MSUE article: A homeowner’s guide to nutrition and fertilization of landscape trees and shrubs, Bert Cregg, Ph.D., Michigan State University, Departments of Horticulture and Forestry, at this link:

Nutrition_and_fertilization_BertCreggfinal.pdf

What commonly causes bark scarring on Japanese maples?

Japanese maples have thin bark, so several issues can create scars. Based on university extension diagnostics, the most likely causes are:

1. Animal feeding (very common in Michigan winters)

Rabbits remove bark in clean, spoon‑sized scrapes near ground level, often during winter.

Voles create irregular patches of bark removal at or just above soil level, often hidden under snow. Trees may “die suddenly” later if girdled.

Deer rubbing produces long vertical shredded bark up to ~3 ft high, with polished wood underneath. These are the most frequent causes of trunk scarring on otherwise healthy maples.

2. Canker diseases (less common but possible)

Eutypella canker creates flattened, darkened areas that eventually expose decayed wood in a target‑like pattern.

Nectria canker forms sunken oval lesions with concentric ridges.

Cankers usually expand slowly and often originate at a wound site.

3. Sunscald (physiological bark injury)

Young, thin‑barked maples are susceptible to sunscald, especially on the south or southwest side of the trunk.

Symptoms include:

Discolored bark

Vertical cracks

Bark sloughing off over time

This is common when winter sun warms the trunk, followed by rapid refreezing.

I highly recommend you email all your images to the MSU Plant & Pest Diagnostics Lab to obtain a confirmed diagnosis of the scarring problem.

Their email is <personal data hidden> - Please include your first and last name.

The experts there can also provide you with the best treatment options.

The lab will let you know if they need a sample sent.

The lab may also ask for additional images. So be prepared.

Their website is at this link:

Plant & Pest Diagnostics (msu.edu)

Their Contact Information is at this link:

Contact Us - Plant & Pest Diagnostics (msu.edu)

This link will explain the details on submitting a sample to the MSU Plant & Pest Diagnostics Lab:

Submit Samples - Plant & Pest Diagnostics (msu.edu)

How to properly fertilize a Japanese maple (Acer palmatum)

University extension guidance emphasizes minimal fertilization unless a deficiency is confirmed.

1. Don’t fertilize newly planted trees

Young maples cannot effectively take up nutrients yet.

2. For established trees, fertilize only if needed

Apply fertilizer in early spring before leaf‑out only if:

Growth is unusually slow

Leaves show nutrient deficiency symptoms

A soil test indicates low nutrient levels

Michigan State University also notes that most landscape trees do not require routine fertilization unless symptoms or soil tests justify it.

3. Use the right type of fertilizer

Choose a slow‑release fertilizer with a high percentage of water‑insoluble nitrogen (WIN).

Avoid high‑nitrogen quick‑release products, which can overstimulate growth and stress the tree.

4. Follow soil‑test‑based rates

MSU recommends applying nitrogen at 0.1–0.2 lbs N per 100 sq ft only when a deficiency is confirmed.

5. Maintain good cultural conditions

Japanese maples thrive in:

Moist, well‑drained, acidic soil

Dappled shade

Mulched root zones to maintain moisture and reduce stress

Healthy trees are less prone to bark injury and disease.

I hope this helps!