I've used gly on small seedlings and it worked. Will it work on 4ft pines?

Pure stand or are you trying to rid a mixed stand of pine?

Not sure what you want to protect, but Garlon 4 is our goto spraying fence rows and anywhere else we want to kill rist size trees without hurting the grass. Just need to angle spray head high and use low pressure so there are drops, not mist.

Gly and garlon will kill any sized pine.

I’d need to hear more about the situation before I’d feel good about a recommendation. The gly/Garlon rec is good, but you get pine with gly along with a good adjuvant and coverage.
Are there trees around you want to keep? Do cows graze the area? Are you planting anything after they are killed? Just some of the questions I’d like to know.

I'm trying to kill pine on an abandoned power line without killing deer food.

If possible I’d just run a bush hog over them. Especially if you intend to keep the old power line right of way open.

I’d just use glyphosate if that is all you are after. Id add an MSO (methylated seed oil) or crop oil and roll with it.

Power line is really sloped and hilly. Bushhogged all we could. I'll just use some hot gly. Thanks for the replys.