Editing a report with conditional dropdowns

In my form, I have a 3 conditional dropdowns in my "Loads" table.  My users will first pick a "Grower", then based off of the "Grower" selection, the "Farms" will be filtered.  Then, the user will pick a "Parcel" and then a "Crop Zone".  My conditional dropdowns are working great.

The problem I am having is when the user goes to edit the record after they have created it.  For example, they will have a parcel called "South of Railroad".  The crop zone will be "Corn".  They realize they entered the parcel incorrectly and go to change "South of Railroad" to "North of Railroad".  When they do this, I need the crop zone field to clear out so they are forced to choose a new crop zone.  When it does not clear, the incorrect crop zone will stay in the field box and will cause issues in other areas of the app.  

Another instance where this happens is when my users copy a record and edit the parcel name.  

I have used the form rules to clear out the crop zones whenever the parcel is cleared out, but do not know how to do it if the parcel name is just modified.

Thanks for your help!