Hide an editor field for all but top level categories

Hello. 

Is there a way to hide an editor field in the CMS Section  based upon it's level in the tree?

Specifically, I am creating a category menu to display service groups and the services within each group. 

1. "Accounting Services" will be level one and have an image. 

2. "Bookkeeping", "Budgeting", etc would be level 2 and not need an image. 

If need be, I'll just put a description above the upload field to let users know when to add an image and when not, but it would be a lot less confusing to them if the field was only there when they needed it. 

Thanks.