Prowl?  No.  The only way Prowl will control pigweed family weeds is when they are small you sit the jug on them.

Pigweed, waterhemp, and Palmer Amaranth are not the same.  Very similar but still different. The main differences are when you try to kill pigweed it lives or it dies.  When you try to control water hemp you make it sick and the family comes to visit and hangs around.  When you try to control Palmer Amaranth it gets really mad and it is going to show you!

OK, first a question: When you are spot spraying are you wanting the kill everything regardless or are you wanting to be selective and not hurt the crop?  Generally glyphosate alone just kills the competition and lets it grow better

My best luck on water hemp in a traited crop is glufosinate (ai in Liberty) BUT it has to be Liberty resistant.  Also glufosinate is a contact killer.  If you spray part of the plant you only kill part of the plant.  And it will not necessarily kill the roots.

If I were in a "Kill it! I don't care what else dies" mood I'd mix glyphosate, glufosinate, 2,4-D and triclopyr (2% Roundup, 4% Liberty, and 2% Crossbow)  Actually the Crossbow is probably enough. Remember it is death on soybeans, tomatoes, grapes, and especially the wife's favorite flower.  This mix is death on everything and probably a violation of labelling laws. I'd also throw in some dawn dish soap and defoamer.

Just remember when you walk across the yard after spraying this your footprints will probably show up.  And don't even consider driving the 4 wheeler across the yard if you've been spraying with it.

Don't ask how I know ....