Ascospores and Conidospores
The two most common types of pine tree infection are fungi called ascospores and conidiospores. Ascospores are spores blown on the wind that can create extremely wide-spread pine tree infections. The conidiospore on the other hand, is a fungus that grows on the trees in a gelatinous ooze. The gelatin is spread by rain washing it from one tree down to the roots of another. This type of spread is common in plantings that are very close together, such as what you would find in a natural forest. Both types of fungus cause browning of the needles of the tree.
Normal Needle Shedding
Brown needles can also be a normal part of the evergreen tree's life span. These trees will drop their old needles after a few years. If the tree experiences a good growing year three or four years before, it will suddenly begin dropping a lot of brown needles all at once. This just means that there were a lot of old needles and they will be replaced by fresh ones. Also, if two or more trees are planted too close together the branches that overlap will likely not get enough sunlight to photosynthesize, so they will gradually turn brown and drop needles, leaving bare branches behind.
Pine Tip Moths and Brown Spot Needle Blight
Pine tip moths can cause trouble in pine trees, creating brown needles at the tips of the tree's branches. Diagnosing this condition can be done by breaking off the tip of the branch and looking inside. The insect will have hollowed it out, consuming all of the living wood inside. Pine bark beetles will attack the bark on the trunk of the tree, basically girdling the trunk and causing all of the needles to suddenly turn brown and drop. Brown spot needle blight will cause inhibited growth and eventual death in the tree. If your tree has brown spots here and there in its foliage and does not seem to increase in size year after year, this could be the problem.