Expulsion from doctoral program
My experience is in mathematics, rather than creative writing, but I imagine both fields approach this issue similarly.  Issues of academic honesty have come up when I've served on admissions committees, and they're a huge obstacle to admission.  A previous expulsion for plagiarism could turn an otherwise strong case into a quick rejection.  In order to have any chance, you need to do several things:


You have to give a convincing explanation of what happened and why nobody needs to worry about future dishonesty.  This is not easy, and most people fail to write anything convincing.  For example, if you write "I didn't realize this counted as plagiarism, but now that I know, I certainly won't ever do it again", people will wonder what other ethical principles you might be unclear on (and how you made it to the qualifying exam in a doctoral program in English without knowing what's considered plagiarism).  If you write "I was sloppy, but I've learned from the experience and will be much more careful from now on", people will worry that being careful is easier said than done, and that this is too facile an excuse.  And it only gets worse from there: if you knew it was wrong and did it on purpose, then you really have a lot of explaining to do.
You need letters of recommendation from people who know what happened and are nevertheless willing to vouch for you.  A letter that doesn't mention the plagiarism will probably be ignored, since the committee won't know whether the recommender even knows about it or how their opinion might change if they found out.  (And it's a sensitive enough subject that nobody's going to call up the recommender and ask, out of fear that you would complain that the committee was leaking confidential information.)


I'd recommend starting by trying to recruit letter writers.  If you can convince enough people to write strong letters for you, then you can take the explanation you used to convince them and incorporate it into your personal statement.  If you can't secure enough letters or aren't confident in their strength, then it's not worth applying now.


  I was recently expelled from doctoral program in English for plagiarism in qualifying exam. Although it was for the lack of a citation, I attended a major research university with a zero tolerance policy. 


I should warn you that this sounds like a terrible basis for an explanation.  It comes across like you are saying omitting citations is not so bad and your expulsion was due to an overly strict policy.  Maybe that's not what you meant, but this is a delicate issue and it's important to keep from being misunderstood.