[potonono]

This has a solution for turning it on, so perhaps you can set it to NO to turn it off.

http://stackoverflow.com/questions/2...ld-on-mac-os-x

// Focus TextField
[textField becomeFirstResponder];

// Disable Continous Spelling
NSTextView *textView = (NSTextView *)[self.window firstResponder];
[textView setContinuousSpellCheckingEnabled:NO];