Drilling of tree trunks is an advanced tree risk assessment methodology used to quantify the amount of decay present in the tree. While this is a very useful technique there is the potential for decay to spread in the holes that were drilled. In this research project, two tree species, red maple and tulip poplar were drilled with a small diameter drill bit and a resistance recording drill. Holes were treated with traditional fungicides, microbial fungicides (Trichoderma), or left untreated. After four years, all of the trees were removed and sectioned. The extent of discoloration and decay was measured, and treatments were compared. This talk will present the results of that research project and propose methodology to reduce the impact of drill to detect decay.