Systemic insecticide. We lost 4 trees to pine beetles and another one looked really bad. Mixed that stuff up with water and dumped in on the ground near the pine trees, and the one that looked terrible has new growth now. Too soon to tell if the tree will come back, but it's a good sign.
I dumped that stuff near every pine tree on the property, those fxcking pine beetles are super hard to get rid of.