2-4-D is used as a broad leaf herbicide. It is actually a groth acelerator. It makes the plant go through its entire growth cycle in 7-10 days and therefore it does not have the time needed to polenate. If 2-4-D is used sparenly, one can expect curled leaves yet no complete die off.
Jimmy, that is expected since the plant you killed tying up the nutrients before. Now that the nutrients are free floating, the only plant there to use them is the algae.
