Thanks for your question. Too bad about your plants.  I will try to help you determine what is going on.  Before doing that I need some information:

1).  Did you start these plants inside under grow lights?

2).  If you started them inside, did you bring them outside in a single step, or did you bring them outside for just a few hours and then back inside over a period of a week or so (i.e., a gradual transition)?

3).  If you have initially grown these plants inside in past seasons before bringing them outside, have you encountered this problem in those past seasons?

I will look forward to hearing back from you.  Many thanks.