Pine trees are evergreens but that doesn't mean they don't shed their needles. They shed approximately 25 percent of their needles every year. The old needles, which can be found on the inner part of the tree near the trunk, don't photosynthesize as well, so they turn yellow or brown and fall off. New needles are found on the tips of the trees. If new needles are turning brown or yellow, your tree is probably suffering from pests or disease.
Pests that can kill your pine tree include bark and wood-boring beetles and nematodes. Beetles usually attack older trees. Look for circular holes in the branches or trunks. Unlike the holes made by woodpeckers, beetle holes will not be arranged in neat lines or horizontal rings. Nematodes are microscopic worms that cause needles to turn brown and branches to become brittle. Symptoms appear in late summer or early fall. Infected trees have to be removed because there's no way to control nematodes.
Pine trees are susceptible to several blights and rusts. Look for yellow or tan spots or bands of red or brown on the needles. Does your tree have cankers, and does sap bleed from them? Do you see galls with orange blisters? A large number of dead needles, branches or twigs dying throughout the tree, or dieback of shoots along with the appearance of resin soaked tissue, all signal disease.
Inspect your tree for injuries caused by lightning, mowers or wind damage. Pine trees are sensitive to wind damage and can suffer from internal injuries that don't show up on the surface. If your tree has visible wounds that cover more than 30 percent of the bark circumference, it will probably die, because the wounds restrict the flow of water and nutrients in the tree and encourage insects and disease to attack. Remove it. You should also remove your tree if more than 30 percent of the live branches are damaged. Remove dead and diseased trees in the winter because the newly cut logs won't attract insects the way they do in warmer months.
Don't be too quick to cut down trees that are partially dead. Instead, remove all dead branches and branches with brown needles or no needles. Don't remove branches with yellow needles. Weakened trees are more susceptible to disease and pests. Reduce stress on your tree by providing it with sufficient water and fertilizer. Clean up fallen needles. Control any insect problems, and wait one year to see if the tree's health improves.