Pine can take stain unevenly. This is why some folks recommend the Pre-Stain conditioner. It is really a thinned poly which seals the pores so the stain goes on more evenly.
Another product which will seal the wood is Zinsser Seal-A-Coat. This is essentially a dewaxed shellac. Very easy to apply.
If you are willing to try a dye instead of a stain, you can mix a few drops of the dye in a cup of Seal-A-Coat and seal and dye in a single step.
You will not find dyes at the big box stores. You will need to go to a dedicated woodworking store like Woodcraft or Rockler.
The dyes are not cheap. Don't be put off by the small bottle, it only takes a few drops.