Never mind. I got it! We need to kill that stump. I'll start another pecan and plant in that area.

Clearly you found your own answer.

We have black walnuts in our woodland. Would I ever let one grow in our landscape around the house or garden? Nope. It isn't worth it because of the allelopathic issues that arise with the juglone. While there are lots of plants that are not affected by black walnut, I just don't even want to have to worry about it, especially since we gather leaves that fall from the trees in and near the yard and use them as mulch and as a compost pile ingredient.