Thus in the field, efforts should be made to encourage the diversity and uniform distribution of the pathogen for reliable data on the field resistance of this ascomycete. Potential approaches to ensure a diverse and abundant source of inoculum for a screening plot would be to have permanent rows of moderately susceptible varieties to supply a diverse source of inoculum, the use of infected potted plants, infected leaves or inoculum sprays, by allowing the accumulation of debris on which the fungus overwinters and/or keeping trials for at least 3 years. The dispersal of the black spot conidia could also be encouraged by the use of overhead irrigation. The general approach for active commercial rose breeders is to plant their trials with no or a minimal spray program. Beyond this, little directed effort is made to increase the inoculum levels although their trials generally contain susceptible cultivars and are frequently planted along side established trials with disease. To ensure they get reliable ratings for resistance they do not rogue susceptible cultivars and run the trial for 2–3 years. The best performing roses are subsequently replanted in multiple sites to expose them to a greater range of pathogen diversity. Nevertheless, field screening will not distinguish the race(s) the plants are resistant to. This type of screening can be done efficiently using a detached leaf screening technique with specific races in the laboratory