Black Pepper Stalks

I've been growing Cayenne and sweet pepper plants in my perspex cube boxes along with my water melons and they've been doing great; starting to flower. But the forked V in between the leaves (where the flowers emerge) have started to go black, and the most developed flower has just withered and died back. I have a chili pepper plant in the same atmosphere which is doing fine. I'm worried if it's too humid in there for them and the black is some kind of rot. It isn't a surface mould; it's the stalk itself which is discolouring. It isn't on any other part of the plants, just at the stem forks. Any ideas :?:

Mine always do that too Mellow, did you get the cayenne seeds from Kitchen Garden Mag?  I did, adn they are doing really well, loads of chillies on them