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Daylily Rust- Where Will It End

© Wesley Ford

Some of us who garden with any regularity have become aware of a "new" disease infecting daylilies (Hemerocallis spp.) in the United states. If we aren't aware of it we should be, and if we are aware of it, we should be very concerned. That is the opinion of Mike Likens, State Plant Pathologist, Virginia Department of Agriculture and Consumer Services.

So what is this new disease that has plant pathologists and daylily propagators so concerned? It goes by the simple common name of Daylily Rust. It's Latin name is Puccinia hemerocallidis. Like most all rust diseases it utilizes an alternate host of a different genus for a portion of its life cycle. We say that it is heteroecious. For this critter, plants in the genus Patrinia serve as the alternate hosts.

But the problem with daylily rust is that like only a few of the rust diseases, it doesn't necessarily require an alternate host. It can short circuit its natural cycle and will successfully re-infect the same host. This is a very important factor, in that you can't break the life cycle by isolating the alternate hosts as you can with most other rust diseases.

Take for instance the Cedar-Apple rust. One portion of its life cycle is spent on apple trees (genus Malus) where it manifests itself as a leaf infection causing necrosis (death) of the leaves and thus reducing the productivity of the tree. Several stages of the 5 stage life cycle are spent on the apple, then the fungus produces spores asexually and these are wafted on the winds to near by Eastern red Cedars (genus Juniperous). The spores geminate and infect the twigs and needles and complete the remaining stages of the life cycle culminating in sexual reproduction and the production of a bright orange octopus-like fruiting body that release spores that in turn infect apples. The cycle repeats itself.

One method to control these diseases, is to use the multiple plant requirement to break the life cycle by removing one of the host plants. In orchard country, cedar-apple rust used to be combated by eliminating all the cedars within several miles of an orchard. In the Shenandoah Valley of Virginia, counties with significant commercial apple orchard production used to have laws requiring that property owners within a certain range of an orchard must keep their land clear of cedars. With the advent of chemical controls these laws have largely fallen by the wayside.

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