The Drakostomes are the bark of the Panakes, which can unleash the deadly gnomish plague. In Book 4: Neverseen, King Dimitar aligns with the Neverseen to unleash the plague so the gnomes will work as slaves for the ogres.
The Cure 
Edit
The only known cure to the drakostomes comes from the flowers of the Panakes. King Dimitar announced to have the cure to the plague, although it was later revealed to be a fake. When Sophie, Keefe, Fitz, Biana, Alvar, Calla, Tam, and Linh break into Ravagog they plan to steal the cure but when Sophie and Fitz sneak into Dimitars mind they figure out in the chest was the plague not the cure. They didn't want to tell Calla but she knew from the former roots.
The Sacrifice Edit
Calla also knew from the roots that the Panakes were the old dead gnomes. So Calla sings a song before telling everyone she must sacrifice herself to be the cure. Sophie originally tries to convince Calla there is another way, but Calla doesn't change her mind. Then the next morning overlooking the ocean was a beautiful tree with braided bark and flowers that turned from blue to pink to purple at Havenfield. The trees blossoms were the cure for all the gnomes with the plague.
