This spring my Green Mountain maple looks terrible, and I can't figure out if the problem is a fungus or a pest. The tree is not ancient - it's about 15 years old. The new leaves are shriveling and blackening. It is worst on the lower branches, but appears to be spreading. I've found several hairy little black and yellow insects on the leaves (about half an inch long), but don't know if they're the problem or not. Should I call an arborist?