chalyse said:Last night I bumped into a helpful FAQ on the American Hemerocallis Society website after searching for info on "daylily summer dormancy." What I was looking for was included in a section on "What diseases affect daylilies?" and just below the nod to summer dormancy there was an entry for rust which mentioned avoiding excessive nitrogen and inadequate potassium nutrition. I don't know what level would be considered "excessive" (??), and I'm sure the nitrogen/alfalfa mentioned here must not even be in the same realm as what is meant, but the juxtaposition caught my eye and may make others wonder, too?
So, now I'm curious about what the possible link might be between rust and high nitrogen or low potassium, because I was also planning to use some nitrogen sources like alfalfa or chicken manure. Having had some fertilizers "burn" plants after use, I try to be careful about possible impacts, and if the "excessive" use of mild fertilizer mixtures can do that to my plants, I wondered if other sources of nitrogen might also?
I suppose it is possible the information has been superseded, since rust is also referred to as a "new" disease, so it may have been written almost 15 years ago. Does anyone know, though, where that association may have come from? Hate to bother @sooby again but hoping she might be able to clarify for us?
The section appears about 3/4 of the way down the page here:
http://www.daylilies.org/AHSfa...
It's not a bother, and in this case I'm certainly the person to "bother" since I'm the one who wrote that part of the AHS FAQ
What is "excessive" N is a good question and is something that would probably need to be researched as far as a connection with daylily rust specifically is concerned. (As an aside, I would be cautious with chicken manure because it can be alkaline so you wouldn't want to use it for daylilies if your soil pH is already above, say, 6.5).
Nutrient levels and pH have an affect on plant diseases. The reference to high N and adequate K in regard to rusts comes from Marschner's Mineral Nutrition of Higher Plants, Academic Press. There is a table that shows increased severity of Puccinia rusts with high N, and decreased severity with higher levels of K. In the text it is suggested that there is a difference between obligate parasites (e.g. rust) and facultative parasites (e.g. Fusarium) in this regard.
"As shown in (table) a high nitrogen supply increases the severity of infection by obligate parasites but has the opposite effect on diseases caused by facultative parasites, such as Alternaria and Fusarium, and most bacterial diseases, for example Xanthomonas spp. In contrast to nitrogen, potassium elicits uniform responses: high concentrations increase the resistance of host plants to both obligate and facultative parasites.......".
The chapter goes on to say that stem rust in wheat increases with increasing nitrogen, the most resistant plants being N deficient. As far as K is concerned, the text states that the response to K is usually confined to deficient plants: "that is, potassium-deficient plants are more susceptible than potassium-sufficient plants to parasitic diseases of both groups....." and "Beyond the optimal potassium supply for growth, no further increase in resistance can be achieved by increasing the supply of potassium and its content in plants."
The reference to a "new" disease doesn't mean the FAQ was written 15 years ago (rust only started being noticed around 2000 and it would have been a while after that that I wrote it but I don't remember when for sure). It was meant to convey that the disease hadn't been around in North America long enough for there to be much information on cultivar resistance and susceptibility. That's pretty much still the case.
Regarding fertilizer choices we often talk about specific ratios, such as 3-1-2, or analyses such as 24-8-16 or 20-20-20, but rarely are the amounts applied per unit area mentioned which is also important. For instance you'd need to use a lot less 45-0-0 than 5-1-2, you wouldn't apply them pound for pound (nor compare the costs by the lb of total fertilizer bag weight but by the cost per lb of the nutrient you're going for, such as the cost per lb of N in the bag).
