Well, the only real one is a fungal pathogen and it's not particulrly effectivem harder than heck to get approval for, like any biological agent and seldom does much other than reduce the impacts of the invasive weed, rather than control it.
The pathogen for Hydrilla also needs a lot fo help to get into the weed first, before becoming effective. In other words, much like Nano technology and Hydrogen supplies for cars, it sounds sexy, but it's even less likely to have a large impact anytime soon. The pathogen often lives outside the parameter of the weed as well. Many pathogens are not particularly selective either and often attack non target plants etc.