Killing and Preventing Fungus Wood Rot

Please read and advise on killing and preventing future fungus and wood rot on the underside of my deck. For a couple of years, my 8 year old deck has been showing signs of white fungus and wood rot in a couple of areas on the underside that are in the dampest locations. The deck is 8 feet above a patio, so there's lots of air circulation - but it's super humid here in Tennessee and summers are hot. The deck is partially shaded and fully PT and the decking is PT 5/4. I have cleaned and stained the decking and tops of railings every two years - and it looks fine on the top side. I began to notice a few decking boards looking dark and feeling soft, and of course there was much more fungus eating away at places where two pieces of wood are in contact with each other on the underside. I have replaced a few of the 5/4 sections that were getting soft. Some sections of the joists and stringer are also being affected and I need to kill and prevent this from getting worse. What is the best thing to spray on the unstained structure and decking in areas where the fungus keeps growing? I'vet spritzed some vinegar on the spots where it's growing but figure there's a better solution. Thanks for the advice !!