Daren Mueller, Plant Pathology, (515) 294-1741, firstname.lastname@example.org
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, email@example.com
Yard and Garden Column for the Week Beginning May 28, 2004
An Update on Daylily Rust
By Daren Mueller
Iowa State University Extension
For daylily enthusiasts, the word 'rust' may not strike fear like it would have a few years back. After its introduction into southeastern United States in 2000, daylily rust exploded onto the national landscape. While nurseries and hobbyists still struggle with this disease in the southeast United States, it thankfully doesn't appear to survive here in the Midwest; yet.
So much was made of daylily rust, and rightfully so, when it was first introduced into Florida. Here was a disease that infected one of the most popular herbaceous perennials that has been considered highly resistant to most pests. Because of widespread shipping, the rust is repeatedly being re-introduced into the Midwest. We have already received plants with rust at the Iowa State University Plant Disease clinic this year that were shipped from Florida. It should be only a matter of time before it can survive in colder climates.
Like many other rust pathogens, the daylily rust pathogen needs a secondary host, in this case Patrinia, to complete its life cycle. Patrinia is a seldom-used ornamental. As far as I know, the rust infects Patrinia in Japan but has not been seen on Patrinia in the United States.
What does that mean for us? The probable reason the pathogen has not survived in the Midwest is that the reddish-orange spores we see on the daylily plants need green tissue to survive, thus are not capable of surviving the Midwest winters after daylilies go dormant. As winter approaches, these reddish-orange spores turn black. These black spores survive the winter and can produce another spore not capable of infecting daylily plants, but do infect Patrinia in the spring. The life cycle will be completed when spores produced on Patrinia will infect daylily. This two-host rust life cycle seems complex and somewhat far-fetched, but actually happens quite often with several rusts on other plants such as cedar/apple and wheat/barberry.
By continually shipping infected plants from the south, we increase the chance of spores from daylily infecting Patrinia, allowing the pathogen to complete its life cycle and enabling the pathogen to survive in the Midwest. The daylily rust pathogen can survive colder climates in its native land, Far East, by doing exactly this.
There are two situations that daylily enthusiasts should be concerned about; preventing daylily rust from getting in your gardens and dealing with infected daylilies already in your gardens.
If you are concerned about daylily rust, there are a few simple steps you can take to lower the chances of introducing this pathogen in your garden. First, purchase plants from a nursery that is 'rust-free.' If the daylilies have come from a nursery with rust or have had rust in the past, you can cut plants back to the crown and/or spray with a fungicide that will kill the fungal spores (e.g. Compass, Daconil Ultrex, Dithane T/O, Heritage, Phyton 27). Please read and follow label instructions carefully.
Also, chose resistant cultivars or more importantly, avoid very susceptible cultivars. A list of over 80 cultivars' reactions to the daylily rust pathogen is available in The Daylily Journal [volume 58, pages 348-351]. Screening cultivars and understanding the genetics of resistance are areas needing continued research. Shortly after the cultivars' reactions were published, researchers in Georgia found a different strain of the fungus that was able to infect previously considered 'resistant' cultivars. What does this mean? If you purchase a 'resistant' cultivar, there is still a chance that you may have a strain of the pathogen that will be able to infect your supposedly 'resistant' cultivars.
If possible, separate newly purchased plants from the rest of the garden until you are confident no rust will develop. A minimum amount of time has not been established, however, six months often has been suggested.
If you have infected daylilies, there are a few options to slow or eliminate the spread of rust. One option is removing infected plant material. Also, several fungicides are considered highly effective against daylily rust (see list above). Again, read and follow labels instructions carefully.
Although winter survival of the daylily rust pathogen has not been seen in the Midwest, reducing the amount of inoculum (mostly the black spores found as winter approaches) lowers the chances of this rust completing its life cycle. There are some simple things that can be done to reduce the chance of the fungus overwintering such as cutting plants back to the crown and apply fungicides (listed above) late in the fall.
If you suspect you have daylilies infected with rust, please contact your local ISU Extension county office or send your sample to the ISU Plant Disease Clinic323 Bessey Hall, Ames, Iowa, 50011, (515) 294-0581 or on the Web at http://www.extension.iastate.edu/Pages/plantpath/pdcintro.html. Let's all try to do our part in keeping daylily rust out of the Midwest.
Editors: Two color photos, suitable for publication, are available at right. Click on each thumbnail photo to go to the fullsized photo. The top picture's fullsize photo is 1.8mb and the bottom picture's fullsize photo is 300K.
Caption: Black spores on a daylily leaf
|Caption: Rust on a daylily leaf|
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