If it didn't produce flowers then you could try taking out every plant that is flowerless. The fulvas tend to have paler foliage but that's the only way I can think of to differentiate. Even if you dig everything up, if some rhizomes or parts of rhizomes still remain in the soil then they'll come right back. It may just be better to take out your fancy hybrids to a new bed, and leave that bed to the fulva (or go at it with herbicide after you've taken the others out).
