I can't really say what is wrong with your Scotch Pine. It could be winter burn or it could be salt damage or if your sprinkler hits them it could be from that. You might want to consider having a certified arborist take a look at them and help you figure it our. Make sure that they are certified. Here is a link to info about disease issues that you can compare to your trees but it doesn't really look like any of those things to me. http://apps.extension.umn.edu/garden/diagnose/plant/evergreen/pine/needlesonebranchdie.html . Here is a link to finding an arborist. http://www.treesaregood.org/