You can't see from the cab where it's good and bad?  I'd never want to take out what are likely your highest yielding plants to replace with less yield potential. 

Even if the patches are sporadic I'd run the same guidance lines from planting to not run down any crop and then drop the planter in the ground when it's thin and lift when it's a good stand. Could redo the whole field that way if needed and just drop/raise to only get the bad spots