It has to start with the planting.  Is the soil and sun/shade conditions the same for this plant as the other two?  What type of soil do you have there, clay, sand, etc.  Does it dry out or remain moist?  Has any weed prevention been done in the area?  Was the planting hole loosened up or just a small hole that the roots were dropped in.  The plant honestly looks like the roots are rotting.