Taking out carpet runner on stairs

Q: My entire stairway is stained oak with a carpet runner that I want to eliminate. I am painting the spindles and risers white. I planned to stain the banister and tread a dark walnut or ebony. When I removed the carpet I found that the center of the tread had never been stained. What should I do to get a seamless dark stain on the tread?

A: The entire tread has to be fully sanded or cleaned of any existing finish and stain and prepared to receive a stain. Not a job for a DIY.