Does fertility effect blackspot?

I found this while searching the web. Your comments are appreciated on the following from the University of Saskatchewan .

Study 2: Evaluation of fertility level, nitrogen source and topdress treatments (Container)

Two products were evaluated (19-5-8 HighN + Minors, 8 - 9 month; Osmocote 18-6-12, 8-9 month) at three levels (1, 2 and 3 lbs actual N/yard3 of media). 19-5-8 HighN is designed to release at an initially high rate and then taper off to a lower but steady rate. Osmocote release rate is mainly influenced by temperature in that when media temperature is low, release rate is low. Urea (46-0-0) was added to the Osmocote treatments to offset the initial slow release. Species used in this study were silver dogwood (Cornus elegantissima variegata), cistena sandcherry (Prunus x cistena) and hardy shrub rose (Rosa arkansana

I think the answer is YES. Lack of soil fertility can reduce resistance to blackspot, and I think that lack of water is an even more important factor. I know these things because while I am only a hacker at hybridizing, I am a master of the art of Rose Torture by Pot Cultivation, and have sent many a vaunted rose into spiraling sickness