beckygardener said:I wonder how long rust stays dormant in a daylily plant?
I don't recall any specific test other than the one summarized on the link below from my rust site, in which it was latent for a minimum of seven weeks because environmental conditions weren't conducive to sporulation. It could be longer than that, for example it may overwinter inside the foliage where the weather doesn't get cold enough to kill the daylily leaves. In ideal conditions (for the rust!) the infection is only invisible for ten days to a couple of weeks.
http://web.ncf.ca/ah748/latent...
Regarding irrigation spray - overhead irrigation would favour most fungal foliar diseases and it's most likely something like the leaf streak fungus getting into the insect damage that causes the brown spots with aphid/mite feeding. Another way to confirm rust besides the tissue test is to look at the spots with a magnifying lens. Rust is the only daylily disease that causes raised spots with yellow/orange spores. Sometimes you may only see the raised bumps if the spores have been blown or rained off. Bringing a suspicious leaf segment indoors and putting it in a plastic baggie (in a lid or something so that the plastic doesn't contact the leaf) for a day or two may make the spores more visible.
It is possible to just see flat brown spots with no raised bumps of spores in daylily rust if the cultivar is resistant but that wouldn't likely happen without some other plants sporulating because without spores there's no rust.
Unfortunately I've heard of several cases where plants were destroyed unnecessarily due to misdiagnosis.
