GA Prime is right about the difference between Surmount and remedy, except Surmount also has fluroxypyr herbicide in it, which I can't use here as it is extremely toxic to fish and other aquatics. (I live next to a river and have a lot of pond area myself)
Here's a list of herbicides with fluroxypyr as an ingredient: (Surmount is listed)
http://www.fluoridealert.org/pesticides ... .meth.html
Pasture Gard will probably do what ya want too, which is triclopyr and fluroxypyr--if you can use it without a problem. I believe Tractor Supply carries it.
Yes, Remedy is expensive, but not as expensive as Grazon Next.
If you live close to Bryan Texas, I've found that Producers Co-op usually has the best prices on Remedy, Grazon, and other herbicides--and they have cases and cases of it stacked up this time of year.
Roundup won't come close to doing the job on what the op is talking about, plus, it will kill grasses ya want to keep. It will 'hurt' some woody weeds, but sweetgum suckers will just laugh at Roundup and it's generics.
Remedy and 2-4D will kill most of the bad crap, and leave the grass, and not hurt any grass seedbank.
Mix it yourself as Caustic Burno said, or buy Crossbow since you have an applicators lic. Crossbow can be bought for about $65/gallon, but Crossbow only has 16% triclopyr and Remedy Ultra is listed as 60% triclopyr.
I tried 1 gal of Crossbow, and had poor results with it and went back to Remedy Ultra.
There are a couple of generic versions of Remedy Ultra available at places like Keystone Pest Solutions.
Here's an older post by Dun about Surmount with more details.
viewtopic.php?f=14&t=66152
The only way I would mow first, is if I was going to IMMEDIATELY hook on a sprayer and spray the crap out of the brush as a cut stump procedure, but you are better off imo, doing the cut stump thing with a backpack sprayer and spraying it hard and heavy with herbicide mixed with a penetrant like diesel. If you wait too long, the cut stump of even small brush or saplings scabs the cut surface off with dried sap, and you wasted time and $$. I try to cut stump spray within 30 minutes, especially with sweetgum--they are tough to kill.