Answer: Since they have been fine in your soil for all this time, I would tend to consider other problems first. Unfortunately, pines are potentially subject to a number of pests and diseases which include the symptom of dropping needles. I would strongly suggest you consult with your local county extension (or on site with a professionally trained and certified arborist with experience working on residential ornamental trees) and get a specific diagnosis of the problem. Based on knowing that, you can decide how to proceed. I'm sorry I can't be more helpful long distance.
Q&A Library Searching Tips