“Can a wife sign her husbands name to a credit application without his knowledge?”
She can sign it, but will he be held accountable is the real question. And there may be some accountability to you with your marital assets while you are married (half is hers, anyway in a community property state). Now that you know about it you should notify the credit agency imediately that you did not sign the application and request to be removed from the account or that the account be cancelled. I suppose if she had power of attorney, and this was within the scope of that power she could both sign it and you could be held accountable.
If you are going through a divorce, and you want her to take the whole amount, I might argue that she breached her fiduciary duty to you when she took out credit in your joint names without your knowledge.