Parse DateTime Without Allowing Default Values?

I currently receive spreadsheets from clients which include several date fields. Since these are coming from many different sources, the date formats can vary widely (although they will all be US format). It could be "April 19, 2010", "4/19/2010", "2010-04-19", etc. I would very much like to use the DateTime.Parse function rather than having to write my own parsing function--I don't want to have to write out every possible combination of date strings.

The problem is, the DateTime.Parse function includes default values if all values are not supplied. So if the field comes in as "03/2009", since no day was specified, the function will return a datetime equivalent to "3/19/2009" (today's day along with the values given). I cannot use this. If a client provides a date that is incomplete, my program must produce an error, not fill in default values for them. Is there a way to tell DateTime.Parse not to use default values? Or perhaps there's another function that can parse multiple string formats into DateTime type without using defaults?