Peach Tree Borer

We discovered peach tree borers in our stone fruit trees. We dug out the oozy eggs from the base of each tree and now have a trench around the trees. We are going to fill with gravel as Michael Philipps recommends in his book Holistic Orchard rather than backfilling with soil. I am also going to mix in some DE with the gravel. I see where the borers also entered at the SW side of trunks (we have not ever wrapped them but will now). One online site recommends filling holes on trunk with a paste. They say to "take wire, poke the holes out as much possible and then make a solution of Diatomaceous Earth and fill the holes with this. You can either use a syringe to do this, or you can reduce the water and just pack it into the holes. Complete this by using window putty or plastic wood to seal the hole."

My question is I do not want to use window putty or plastic wood, as it is not organic. Any other ideas to seal the hole? I am not sure what plastic wood even is...

Thanks,
Beth
Idaho 7B

This is plastic wood, I've used it for many wood projects and it holds up very well.

http://www.dap.com/product_details.aspx?BrandID=147&SubcatID=24

I agree it's unlikely to be organic but I think the air-born and water-born pollutants would be more of an issue.

You might try DE and then fill it up with a safe clay and allow the plug to dry in place slowly, or make a flour and water paste and plug the hole with a hardwood dowl.