Sent this question to Bonnie's 'Ask the Expert' and they said it looks like fertilizer burn. I highly recommed asking over there as they will reply within 24 - 48 hours...

So how did they figure that out with the minimal amount of info you gave us?

And did you fertilize? If so, with what? and when? and how often?

Or does the bed have lots of manure in it?

Inquiring minds would like to know.