Here is an excellent publication on herbicide carryover. Lots of folks use manure from there livestock, that have been grazing on forages treated by herbicides, to fertilize their gardens.The chemical residue from 2-4D based products and many other herbicides can damage or kill your plants. A lot of the chemical residue can be destroyed by composting for at least 30days if they reach a high enough temperature.
http://content.ces.ncsu.edu/herbicide-carryover.pdfJust food for thought!