Dark stain on pine

Use a pre-treatment. They sell a conditioner, but I get the same result just putting on some mineral spirits, let sit for 10 minutes or so, then stain.

Alternative method is to put a spit coat of 1 lb. shellac first.

If you use something like Minwax's Wood Conditioner, let it cure overnight. The two to three hours recommended in the can directions is not enough to fully prevent blotching.

You may need to experiment to find just the right solids content for the shellac washcoat but a 1 pound cut is a good place to start. You may need to use a lower cut.

You might also consider using a gel stain as most of the stain lies on top of the wood and does not penetrate well.

Good Luck.