Where is it?
Yes the sweetgums are taking over.
What is your goal. You mention converting it to pine and reseeding.
Honestly, open pasture / hay ground will be the most labor intensive to maintain. On top of that the chemical / fertilizer / mowing etc is pretty much wasted if you aren't bailing it or running livestock on it. Hay ground / open pasture is pretty much worthless to the wildlife as well.
Converting it to timber. Depends on where you are. Pine plantation isn't a great yield and is a long term thing (20 to 30 years to get a return). It is good for wildlife though and is not labor intensive at all. You'd basically spray to kill out what you have and pay a crew to come in and plant your trees.
An idea I'll throw out is consider native grasses / plants. You can get some cost share from organizations like Quail Forever and Pheasants Forever and possibly from your state as well. Would be similar to converting it to pine plantation in that you'd wipe out what is there now and start over. You wouldn't necessarily do the whole thing the same either. You could strategically plant woody / bushy type cover "islands" and break the rest up into plots of native grasses with fire lanes / trails separating them. It turns your land into a wildlife haven. Small and large mammals, birds, bees and other pollinators, etc. Best part is your maintenance is low after you get it established. No fertilizer needed. You'd only mow your trails / fire lanes a few times a year. If you break it up into sections you manage it by burning the sections with prescribed fire on a rotation (one or two little sections a year).
MDWFP - Old Field Management
https://extension.tennessee.edu/publications/Documents/PB1855.pdf