The Dryad's Cursed Forest

At one point in history, the Dryad's Cursed Forest was once a lush and green forest with abundant life. It likewise was vital for the populations living in and around it, helping the people with anything from timber to the hunting of game.
No one knows when it began, but over time, the forest slowly turned into the cursed forest that stands today with dried and the dryads that were not able to escape by transferring to other trees or with the help of the people, like the trees turned into dried and gnarled up versions of themself and began to roam the forest killing anything and everyone, leaving the forest as an empty shell of its former glory.
The dryads that were able to escape reported that one morning, a thick fog had engulfed the entire forest and that the trees had trouble seeing the sun just as they were about to lose hope, the fog lifted and for a while they were relieved that it was over but then a few days after the fog had lifted, the first three began to dry up and slowly but at a steady pace, the trees surrounding it began to dry up and wither away, at first the dryads thought it was some disease but when their magic proved useless they got worried, the worry only increased when the sickness reached the trees that were home to the dryads and the dryads just like their trees began to be infected and turn into twisted and sick versions of themself, many dryads fell in the attempt to help those infected.
What both scholars that have since studied the forest and the dryads find weird is that once the sickness reached the end of the forest, it stopped spreading and in some places, its even receding slowly.