[rat]

2,4-D and 2,4-DB are very very similar. Both are broadleaf-specific herbicides and have virtually zero activity vs. grasses. This is why site preparation is better done with a broad-spectrum product like usfwc mentioned (glyphosate, roundup).

The difference between the two lies in the chemical structure. While 2,4-D will kill most all broadleaves (including broadleaf crops like soybeans), 2,4-DB has some selectivity of legumes like beans, peas, forage legumes. Higher plants use beta oxidation to metabolize 2,4-DB into plain ole 2,4-D and end up dying. The legumes I mentioned cant do this so they survive. A word of warning though... spraying 2,4-DB is a rate and timing specific enterprise so make sure your sprayer is calibrated and pay close attn to the label... some crop injury will undoubtedly occur so be prepared.
OR, just dont worry about a little clover in your beans. Its a foodplot right?

2.4-D's are efficient at taking broadleaf weeds out of narrow leaf crops like corn, sorghum, small grains, etc.
Use a product like usfwc mentioned to take grassy weeds out of your broadleaf food plots.

 

[rat]

There is SOME residual effect but it is not long lived and only the most sensitive broadleaf plants are normally affected.
It is not a very efficient residual on its own, but you can have plantback problems with sensitive plants (beans, tomatoes, etc).

 

[rat]

It would be illegal to sell a registered pesticide without proper labeling and identification.
If it is 2,4-DB it will (and must by law) say 4-(2,4-dichlorophenoxy)butanoic acid.
If it is jujst 2,4-D, it will say(2,4-dichlorophenoxy)acetic acid.
Just check the label to be sure.

That said, is there any reason you dont just use glyphosate (Roundup)? There are no plantback worries with it.