Hello Brendan,

Yellowing leaves with spots on a Mutsu apple tree can be caused by a combination of nutrient deficiencies, fungal diseases, pests, or environmental stress. In Michigan’s climate, several pathogens are common, so accurate diagnosis is key.

Likely Causes

1. Fungal diseases

Apple scab – Dark olive-green spots that may yellow and drop leaves; thrives in wet, cool conditions.

Cedar apple rust – Bright orange-yellow spots, often with a darker border; requires nearby junipers or cedars to complete its life cycle.

Powdery mildew – White powdery coating that can cause yellowing as it progresses.

2. Nutrient deficiencies

Magnesium – Yellowing between veins, herringbone patterns in new leaves.

Iron – Yellowing between veins with green veins (chlorosis).

Nitrogen – Pale green to yellow leaves, stunted growth.

3. Pests

Aphids – Curl leaves, leave sticky residue.

Spider mites – Fine webbing, speckled or bronzed leaves.

Round-headed apple tree borer – Holes in trunk, frass near base.

4. Environmental stress

Overwatering – Soggy soil, root rot, yellowing leaves.

Underwatering – Dry soil, wilting, leaf curl.

Alkaline soil – Reduces nutrient availability.

I highly recommend you send all your images by e-mail to the MSU Plant & Pest Diagnostics Lab to get a confirmed diagnosis.

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)

I hope this helps!