Erysimum problems
 

since moving to a house along the Carmel River in Carmel Valley village, the various Erysimum species I have been propagating (E. capitatum, E. franciscanum, E. concinnum and E. menziesii) have all shown varying degrees of decline from what appears to be some sort of rust type fungi. The problem shows up as very powdery looking light sulfur yellow patches on the tops of the leaves. The leaves eventually curl somewhat and then the plant dies. I have spread the various species far apart in my small (15' x 70') nursery space in varying degrees of partial to full sun. Only the Erysimum species, out of maybe 100 different total plants being propagated, are showing this problem. Does anyone know of a specific fungal parasite that is genus specific to Erysimum?
And then of course, a way to prevent it from wiping out my collection?

According to a RHS site the species is affected by downy mildew and bacterial leaf blight.