Hello Becky,

BASED ON WHAT I SEE FROM YOUR IMAGES:
Your apple tree does not show black rot or borer injury. This is graft wrap — not disease. The black sections you’re seeing are the edges of the
grafting tape/parafilm wrap, which is beginning to weather, loosen, and
discolor.

This is normal and not a disease, and it explains why:

The black areas are perfectly aligned with the graft
union

The bark underneath looks healthy and smooth

There is no cracking, oozing, or canker margin

The discoloration is on the wrap, not the wood

The branch structure is uniform and not sunken or dead

This is exactly what grafting tape looks like after a season or two outdoors — it begins to degrade, peel, and darken.

Why were wasps interested?

Wasps are often attracted to:

Sap weeping from graft unions (common in spring)

Sugars on degrading graft tape

Moisture and shelter around wraps

They are not causing damage — they’re opportunistic visitors.

What you should do now

1. Remove the grafting tape CAREFULLY!

If the graft has fully healed (and it looks like it has), gently remove the wrap:

Cut it carefully with a utility knife or pruners

Peel it away from the union

Avoid pulling hard — you don’t want to tear bark

This will eliminate the black appearance and reduce insect interest.

2. Inspect the graft union

Once the tape is off, check for:

Smooth, continuous bark

No cracks or sunken areas

No frass (sawdust-like debris)

No oozing sap

If the union looks clean, you’re done.

3. No chemical treatment needed

There is no disease present in your photo.

No fungicide, insecticide, or pruning is required.

If you want absolute confirmation - VERY IMPORTANT!
You can send a photo to MSU Plant & Pest Diagnostics, but based on what I see, this is a healthy graft union with aging wrap, not a pathological condition.
MSU PLANT AND PEST DIAGNOSTIC LAB IS NOT DOING EMAIL REFERRALS FROM IMAGES RIGHT NOW. THEY ARE BACKED UP! IN OTHER WORDS, THEY ONLY DIAGNOSE SAMPLES!

If you want a precise diagnosis
Send to the MSU Plant and Pest Diagnostics:

A SAMPLE OF A BRANCH WITH GRAFTING TAPE. WITH THAT SAMPLE, PLEASE SEND ALL YOUR IMAGES. I strongly suggest you call them if you have any questions.

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

Bottom line
Your McIntosh apple tree is not infected — the black areas are old grafting tape, and the wasps were simply attracted to minor sap or sugars around the wrap. Removing the tape will resolve the issue.

I hope this helps!