Hi, everyone,
Fred, months ago on the Rust forum I used your experiences with rust (i.e., seeing a marked decrease of it over the years) to question whether daylilies could acquire resistance. There were many responses. One was that it’s unlikely that Systemic Acquired Resistance is occurring. Instead, other rusts tend to develop a resistance to fungicides, which is why rotating fungicides is recommended. Also since commercial nurseries are spraying to contain rust, there are fewer rust spores in the environment, which results in less severe infestations.
Applying knowledge from studies of other plants, it may be possible (but not proven) that adult daylilies may show rust resistance, but not when they’re seedlings. However, the reverse is also possible in the plant world. In other words, a seedling that shows rust resistance, could develop rust susceptibility when it reached ‘adulthood.’ However, no one knows how to define what it means for a daylily to be an adult. And once again: this hasn’t been studied, so no one knows whether it applies to daylilies.
It was also mentioned that daylily rust has existed in Asia for more than 100 years, and affects native daylilies severely. What’s interesting about this is that the native plants are dormant and die back completely in the winter, so theoretically they shouldn’t get rust in the following season. (Patrinia wasn’t brought up in this post, but certainly if it’s in the area then that would explain the continued daylily blight.)
Another possibility: in the last 10+ years, hybridizers at the very least will not register a seedling that shows rust susceptibility. This could also account for a decrease of rust among the newly acquired daylilies in your garden. A breeder of dips in Arkansas mentioned that when rust first appeared 75% of his dips got rust. Now, it’s about 25%, and he believes the marked decrease has to do with his breeding for rust resistance.
There was also a differing opinion about the success of breeding for rust resistance. One hybridizer found that of newly purchased daylilies from hybridizers claiming them to be highly rust resistant, 50% turned out to be of only average rust resistance in his garden. He also spoke about daylily rust having “good years and bad years,” in the same way that daylily performance varied from one year to the next. This is where differing environments/garden settings may come into play.
Here’s a very technical article that explains graphically the factors that affect the development/appearance of a plant disease. (Note that environment – climate, humidity, etc. – is one of the key factors.)
http://www.apsnet.org/edcenter...
I would urge anyone with a deeper interest in rust to join Sue Bergeron’s Daylily Rust Forum by sending an e-mail to:
[email protected]
Sometimes discussions are very technical, which is to be expected since among the participants are plant pathology and genetics experts. But they also provide very practical information. I’ve found reading the posts (and especially the archives!) to be very helpful. Rust is a very complicated subject, and in my opinion hasn't been studied nearly enough for any of us to have a good grasp of what we're up against.
I heartily agree with the suggestion that Ed made (on the Rust Forum) months ago that ideally we need a lab to which we could send rust-infected leaves, so that an independent analysis of rust could be made, and an objective scale of rust resistance could be developed. At the very least, we could determine whether there is more than a single strain of rust in the North American continent.
All the best - Elizabete
Thanks everyone for sharing your experiences!!
