Cindy,
I cant see how Round Up could be a alternative to 2,4-D (2,4-Doichlorophenoxyacetic acid), there two completely different types of herbicides.
Round Up is a herbicide that kills all types of plant life where as 2,4-D only kills broad leaf plants (Dicotyledon's).
If you spray a lawn with Round Up it will kill everything (grass, weeds, etc.) but if you spray or spread 2,4-D on a lawn it will only kill broad leaf plants and the grass will be unharmed.
The same can be done on a field of heirloom corn, you can spray the field with 2,4-D and the corn is unharmed but spray that same field with Round Up and that corn will die..
Is one safer than the other,,,,, I cant say but will say that both will do more harm than good if in the wrong hands.
I have always said that the average "home owner" will do more harm than a farmer will when using products like Round Up, 2,4-D and Burn Out (a organic weed killer containing Sodium Lauryl Sulfate (SLS) ).