Karen, I'm not sure I fully understand the question about dormant spores appearing? Rust lives invisibly inside the plant as fungal threads. Eventually these produce reproductive units called spores that you can see from the outside of the plant. This is similar to a plant producing seeds. In the case of rust, the plant is the fungus and the spores are the seeds.
Because the fungus lives inside the plant, you need for these fungal threads to die, it isn't enough to kill the spores on the outside of the plant if there is fungus inside the plant that has not yet shown itself by producing spores.
It has not been determined exactly how long the fungus can stay alive inside leaves without sporulating (producing spores on the outside of the leaf or scape). The only thing we know from a research observation is that it can be seven weeks or longer between exposure to spores and the appearance of the next cycle of spores.
There's more detailed info on this here:
http://web.ncf.ca/ah748/latent...
I'm not sure if this answers your question?
