I am surprised that that article did not mention an alternate host for the disease. All rust diseases complete their life cycle on two very different species. Most rusts must have both species in the environment to persist. (Example:Cedar Apple rust must have both apples (Malus spp.) and "Cedars" (Juniperus spp.) to persist.) However some, like Daylily rust, can continue life by infecting only daylilies.
This is important because different kinds of propagules are produced, depending on which host species propagates them. This can also means different cold hardiness. In the case of daylilies, the type that daylilies produce is not very cold hardy. But the type that the alternate host produces is very cold hardy (at least zone 3). Fortunately, the alternate hosts for Daylily rust are Patrinia species, and I don't think any are native here in North America. However, all of us grow plants native to other parts of the world, and although Patrinia are virtually unknown here, there will always be some who might grow it. In fact, until this spring I was one of them! I grew it as an edible crop, but when I discovered it was the alternate host of Daylily rust, I killed them all. Thankfully, they were never infected, anyway.
