Question
Most of my pine trees have needles that are turning brown on the tip.  what should I do??

Answer
If you are talking about the needled on the very tip of the branches it is an insect called tip moth. This is a moth that lays its eggs on the bud and the larvae hatch and bore into the twig killing the tip. Tip moth will attack small trees and when the tree gets about 20 feet tall you see no attacks. The tip will die but will send out new twigs making the tree more bushy. Tip moths rarely kill tree but can stunt the growth or make them look very bad.
Control depends on if these are small yard trees or a plantation of pines. If they are small trees in the yard the tips can be cut off and destroyed or you can use a systemic insecticide applied to the soil. Sprays can be used but the timing of the spray has to be when the moths are present and will take some monitoring. Imidacloprid is a systemic insecticide that has recently been labeled for use by homeowners. It is sold under the brand name Bayer Advanced Garden Tree and Shrub Insect Control, and, in this formulation, is applied as a soil drench around the roots or ornamental plants, rather than as a foliar spray.

For a plantation I would not recommend doing anything since the growth loss that may occur would be less of a value than the insecticide spray and the timing issue and the need to spray twice will out way the damage. The tree will out grow the tip moth damage and at the first thinning you will not be able to tell the damaged trees from the in damaged.

Here is a web site that has pictures of tip moth.
http://creatures.ifas.ufl.edu/trees/moths/nantucket_pine_tip_moth.htm