A few things...
What zone do you live in & what kind of pine tree is it?
Evergreens do occasionally have needles that brown/yellow up & fall off. Evergreen trees shed their older needles & produce new ones. I'm wondering what zone you live in since in my zone there is a HUGE outbreak of bagworm which almost appear like little pine cones hanging from the tree but are actually worms in a little cocoon type thing feeding off the tree then "hatch" in the spring & kill your evergreen. They're pretty partial to Spruce trees but I've been seeing them around randomly on Concolor Firs & a few others.