GALVESTON – The century-old Ghirardi Oak, a local landmark that League City spent $200,000 to relocate two years ago, is suffering from a canker and that could threaten its survival. The oak gained international attention when it was moved a quarter-mile in an impressive feat of engineering in June 2012 to make way for a street widening. [...] city officials say it has signs of the deadly Hypoxylon canker, a tree disease that is impervious to any known treatment. Several small limbs and five main tree limbs are showing signs of canker infection, and wood-boring insects have begun feasting on the Compton oak in the infected areas, according to a recent city manager's report. The only treatment is to keep the oak supplied with nutrients and good soil conditions so that it has a chance to defeat the canker on its own, he said.