From the Previous Pics It looks like Its In a Low Lying area and Im hoping it's Not root rot.
(this happens when the soil's drainage isnt too good and the roots are constantly sitting in a puddle in the bottom of the hole).

Its kind of hard to Make a diagnosis with out actually being there.
But check the soil directly around the Pant.
make a small hole with a stick or somthing just to see If the soil Is too Damp down below.
I Make small mounds and Plant ontop Just Incase Because I lost a Good Patch a few years ago due to root Rot.

dont Panic Just yet I'm Only guessing here.
see what HARDON has to say He's defenetly a grow encilopedia.(i mean that with all respect)..

ps.New Music on the way today....