I have been fighting sweet gums and other saplings as well as
Jessamine, trumpet creeper, poison ivy, and honey suckle on some land
I own in SC. It was in pines and I had them thinned about 8 years ago
and lost some to to wind and ice and possibly to disease and have
never cleaned them. Every third row was removed so I am starting to
mow between them and kill the saplings. Last month I borrowed my
brother's tractor and bush hog to clear most of the remaining cleared
rows.

I have also been fighting with roundup for a couple years, but a 3
gallon hand pump sprayer or a 4 gallon backpack sprayer is kind of
like peeing on a forest fire. So I just bought an 8 gallon electric
pump sprayer from AgriSupply to try out this month. Also got a 2.5
gallon jug of roundup and a gallon of Trimec broadleaf herbicide.
Will start using it on the next trip back.

Some to these remaining gum "saplings" are 6 inches in diameter. Will
attack them with ditchbank axe, chainsaw or drilling holes in them and
putting in roundup diluted 5:1 instead of the normal 40:1.

I will post a product update later this year.