BT worm killer

[chancethegardener]

I am sorry if a similar topic was started before but I have some major worm problems with my corns. Last year I used BT worm killer on cucumber plants and it worked very well for me.
My first question is: Does BT worm killer work on corns as well?
Second question: I couldn't find an expiration date on the container and I bought it last October. Is the BT worm killer still good or should I buy a new one (also I am not sure what the maximum temperature is that is still good for the bacteria)?
Third question: I was out of town for a few days and when I came back I found out that my corns were highly damaged; however they are still forming ears. I found some worms hiding and feeding underneath some of the forming ears. I killed them however I am not sure if they eat the corn stems on the inside. Should I give up my corns or keep growing them?