Two negative ways of looking at this...firstly if it is correct that diseases like rust, which need living tissue to survive (most plant pathogens do not), do better on or "prefer" healthy plants then that kind of counts against the idea if the notion is to make the plants healthier. In fact there was a paper published many years ago that found being stressed by thrips and other stresses reduced the incidence of rust on some plant species - I'd have to find the article again if anyone is interested (it didn't include daylily rust).
Secondly daylily rust, for a hundred years or so before it came to North America, evolved and happily infected wild daylilies in Asia, in that latter case presumably nature wasn't in balance there either
It is true that nutrient status can affect diseases like rusts, which are favoured by high nitrogen and discouraged by adequate potassium. It certainly also true that problems can be caused by indiscriminate inputs and over-fertilization.
There was a lot of discussion some years ago about aerobic compost tea suppressing diseases although we don't hear as much about it these days, perhaps because it wasn't, according to this article by Dr. Linda Chalker-Scott, supported by scientific testing:
http://puyallup.wsu.edu/wp-con...
I'm kind of doubtful that soil microorganisms would directly affect a foliar disease like rust, but there are other microorganisms called hyperparasites that attack rust on the leaves (in the absence of fungicides of course).
Interesting about the monitor for changing the susceptibilty or resistance in the database, I didn't know that. Even so there is another negative with an either/or definition like that because rust is not that straightforward in the sense that a resistant plant may still show some spots. So presumably someone might rate that either way?
