Do your hemlocks have a grayish appearance?  Are they dropping needles, especially on the interior of the branches?  Then, you may have an infestation of hemlock woolly adelgid. 
The hemlock woolly adelgid (Adelges tsugae), native to Asia, is a small, aphidlike insect that threatens tree health and sustainability of the Eastern hemlock and Carolina hemlock in [...]

Noticing a white “woolly” looking fuzz on your Hemlocks?  It’s a sure sign that the woolly adelgids are making a home in your trees. Once the infestation has taken hold, you’ll notice that the tree has little or no new growth on limbs and limbs will start to die back.
If you suspect that your Hemlocks may [...]