damage from hole through center of pecan tree.

[little1406]

About a year ago, I made a wonderful tree swing for my kids and grandkids (and me) in a huge pecan tree. I made the attachment to the tree by drilling a 5/8" diameter hole straight through the center of a major limb about 30' off the ground. The limb is 9-10" in diameter at this location. Through this hole, I passed a 5/8" diameter galvanized eye bolt. I used a 5" square 3/16" thick steel "washer" on top, curved to fit the limb. This swing functioned perfectly until sometime last night, when the entire upper portion of the limb broke off right at the drilled hole....! I'd quess that the fallen portion weighs 1000 lbs or more. It looked perfectly healthy with lots of green leaves despite the record-setting drought we're presently suffering here in Central Texas. Clearly the drilled hole is a major factor in this break because precisely half of it is on the fallen limb and the other half is still 30' up in the air. Examining the fallen portion, I see a dark brown staining around the hole that extends about 1/2" into the surrounding whitish pecan wood. Also, there was apparently an axial crack that had developed over time 6-7" downwards from the lower half of this hole. The two sides of this crack were cleanly separated in the break and I can plainly see that the brown staining extends along the crack, too....but not significantly INTO the surrounding wood.

Now for my question:

Two weeks ago, I made a nearly identical installation, again in a huge pecan tree, at my son's house.....! What can I do to prevent a similar disaster befalling his tree? Is there any sort of sealant that should be applied to this hole? How about anti-fungal or anti-bacterial solutions that might be applied to prevent infection of the tree? Any suggestions would be greatly appreciated.

Thanks!

Scott Little