Hi Green DC,
You haven't responded to Backyardgardener's links so I don't know if you have found the cause of your problems.* You don't say how you've watered (we had a drought in Maryland and DC last year) and if these were b&b or potted plants.* I can't quite tell from the picture if these are in full sun or not.* Without that info it would be difficult to say what is going on. Some browning of the interior needles is common as the older needles die off.* I can't see excessive browning in your picture.
This site might give you more insight into what might be the cause.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.