beckygardener said:Are there photographs anywhere showing the amount of rust for each rating?
It would be very useful if someone would make a set of photographs or drawings showing examples of the amount of rust on daylily leaves for each rating. Below is an example used for wheat. It cannot be used for daylilies as they may or may not have as much rust on their leaves as wheat does.
Sue's explanation of horizontal and vertical resistance is reasonable. In practice there are difficulties with categorizing plant resistance no matter what simple systems one attempts to use. Living organisms seldom obey our simple 'rules'.
It is not known whether daylilies show horizontal or vertical resistance to rust. It is possible that some cultivars show vertical resistance and other cultivars show horizontal resistance - we do not know. By definition a cultivar could not show both vertical and horizontal resistance.
even if I have rust resistant daylilies, that does not mean they are horizontally resistant? They could just be vertically resistant, correct?
More or less correct but it depends.
In some cases of horizontal resistance the plants would still get some rust just not enough to cause problems or so late in the season that it does not matter. In some cases of vertical resistance the plants would not get any rust. However, it would be very difficult to know which type of resistance is present by simply observing rust in a garden.
