Thanks Michele. It's odd that only one plant looks like that. I have also gotten burnt looking foliage from spider mites. Jim Spencer was loaded with mites 2 years ago and foliage turned brown. I guess different areas of the garden can have different ph's.

Thanks, Cindy, I'm so glad I mis-read that bit, as it seems that rust is slowed around 90 and above, and that research result may well confuse (or possibly clarify) the idea of whether heat is a way to control or kill off rust. Even more reason to clarify ahead of any further internet transmissions whether that means it is possible that it is truly killed off at some temp, like we hear is sometimes the case with certain winter conditions, or just slowed, etc. I well remember not long ago that we were also hearing from some (and still see on some internet sites) that daylilies were "developing immunity" to rust and that there was only one strain of daylily rust ... perhaps these internet memes are other related topics that ATP members can support with discussion and sharing between gardeners in its more open forum?

Becky, perhaps either your rust hasn't read the study or there is some other factor at play between your shade and sun beds. For example is the shade provided by trees in which case the night temperature would normally be lower over the open beds, is there a difference in air circulation, different genetic lines in the different beds, differences in the prevailing wind direction?

Tina, I think if rust could be killed by high temperatures we wouldn't still have it in Florida and Texas for example. I understand it just takes a break during the hottest periods. In the U of Guelph study described in part on my web site (on the spore longevity page, and available in full PDF from there) daylilies were inoculated with rust but no pustules appeared for seven weeks or more during hot weather.

Theoretically if heat killed all the foliage on all the daylilies in an area then presumably it would have the same effect as when winter kills the foliage since the rust cannot survive without living tissue (except as spores which can only infect living tissue) but I don't think it's likely that all daylilies in an infected garden would have total foliage kill during hot weather as happens with cold in the colder climates.

Sue - I appreciate your response very much! I know my front garden bed border of daylilies gets quite hot. Definitely in the 90's if not the 100's. We've been having quite a bit of rain lately, so that may be enabling the rust to grow and spread around my garden beds.

Yes, the shaded raised daylily beds are shaded by trees & the house during part of the day. The foliage on some of the seedlings do show some mild rust, but many do not show any rust. Not sure if they have developed some sort of resistance or if the shade is playing a part in this. Those plants don't look as "stressed" as the full sun daylilies. Could that play a part? I have a mix of seedlings all around. I have no idea what the parentage is on 99% of them, but many have blooms that look similar, so I am guessing there may be some siblings among my 300+ seedlings in the 4 different raised beds (2 partial shade beds, 2 full sun beds).

I will tell you that I moved all the seedlings that are currently in the partial shade beds from the full sun beds. And many of them had full blown rust fungus on them last year in the full sun beds. I am rather surprised that this year some have a slight outbreak of rust instead of full blown rust attack. And some are NOT showing signs of rust at all. I am pretty surprised by this because most of them looked really bad last year. What is your thoughts on this? My area had a very mild winter this year, too. Most of my daylilies are evergreens or semi-evergreens. So they never completely died back to the ground. I don't quite know what to make of this.

For comparison ...

This is what the daylilies look like in one area of one of the full sun raised beds. I do grow other plants in with them. The majority have rust on their leaves just like the seedling that were in that bed last year (which were moved to the shade beds):


This is one area of daylily seedlings in a partial shade raised bed. The leaves were trimmed recently so that I could add the knife markers easier than pushing long leaf fans out of the way. This is a BIG difference from how they looked last year.:


Any explanation why they could be looking a lot better this year? I used the same soil mix, same fertilizer, same watering scheduled, etc. as the full sun raised beds. The only difference that I can think of is the fact that they are in partial shade now instead of full sun.

I think when you cut off the leaves, you didn't just groom your garden, you removed a ton of spore-producing areas on the leaves, which would be sapping strength.

Judy - The spores start on the tips of the leaves? I'd honestly never noticed that. I usually start seeing the rust along the base of the leaves and it seems to spread from there. It will cover the leaves within a week. I didn't see any spores on most of those plants. Some yes has some minor spores along the base and middle of the plant, but I didn't see any spores on the tips. The tips looked as green and nice as the rest of the plant. I wonder if these 2 new garden beds has anything to do with the lack of rust being that these are the very first plants grown in them?

No, if I gave that impression, I apologize. That's not what I meant. You said you trimmed the leaves. When you trimmed, you ridded your daylilies of additional areas that COULD have been producing spores, resulting in a possible slowing of spore dispersal. Less leaf area = less spores. I'm not of the opinion that shade diminishes rust infection. Cutting back leaves, however does slow rust down.

I can see where plants in the shade would stay damp longer than those in the sun and would thus be more susceptible to rust. I have read where many people have found rust to be more of a problem in the shade than in the sun, don't know if that is the reason or not.

Judy - I just recently clipped the ends off my partial shade daylilies, so the tips have been long for several months. The reason I thought that the shade might have something to do with those daylilies having less rust this year (vs. last year) was because they do indeed look much healthier this year. I transplanted daylilies to the front yard as a border as well. Those are pretty much covered in rust except 2 or 3 different daylilies. All the rest in that border look pretty awful. I never had daylilies in the front yard before this year. They are in full sun. The intense heat in that border and the other full sun raised bed in the backyard are both showing the majority of the daylilies with rust. A LOT of rust! They look just like the photo I posted previous showing the rusty daylilies. I also have daylilies in other areas of my backyard. Daylily plants here and there in other garden beds. Those get partial shade as well. They also look better. I have not noticed rust on any of those daylilies. The only common denominator of those and the daylilies in the 2 partial shade raised beds is the shade factor. Most all those daylilies in the partial shade this year, were in full sun last year and had rust last year. So how can that be? I don't treat them for rust. My thought was that daylilies that are less stressed might be better able to resist or cope with rust infection. All the partial shade daylilies now look a lot healthier this year than they did last year in full sun. Could the stress of full sun, intense heat, and the occasional dry situation in the soil be a factor in the exposure and spreading of rust in daylilies? Those harsh environment factors really do cause stress in the plants. I have no other explanation for this.

And I agree, you would think that the partial shade areas would be MORE rust prone as moisture doesn't evaporate as fast in shade as it does in sun. But that has not been the case in my yard. What else could it be?

I am really very surprised that the partial shade beds have such healthy plants. I was concerned that it would be the opposite. Imagine my surprise!

The reason the shaded plants may look healthier and no rust is because the heat may stress the others and make them more susceptible to an outbreak like you said. I have observed that mine that are more shaded (not on purpose, need to trim trees) look better than the ones in full sun. Of course the ones in deep shade tend to get spindly and scapes grow too tall and no branching or buds.
These areas last year I did not spray because we were not keeping the plants anyway and they did not breakout in rust throughout the season until around September (when the fall outbreak occurs) but by this time they were being stressed because I stopped watering them for a few months.

There is more factors that contribute to rust than just moisture as you are finding out

Michele - Thank you for confirming what I am seeing. I know I wasn't losing my mind or imagining things! LOL!

I will have to pay attention to the scapes on my partial shade daylilies. So far, I haven't noticed any difference in the bloom factor from last year to this year on any of those plants that bloomed again this year. They are not in deep shade and do get a few hours of direct sun each day and the rest of the day is filtered sunlight from the Oak tree. I was really impressed with how nice they look this year! I always thought that once they had rust, they would always have rust. But apparently that is not necessarily true. Healthy and happy daylilies can better fight off or cope with fungus, diseases, and pests. I think extreme heat is the real factor in my yard, not so much just sunlight. When the temps are cooler in late Winter, the daylilies all around my yard looked good, but as soon as the temps began rising to 85+, that is when I started noticing the rust on the full sun daylilies. I always thought that daylilies were able to cope with heat and drought ... but that does not mean they will cope well. They just don't necessarily die right away from those conditions. It does weaken them and make them more susceptible to pathogens and pests. Which in turn may be what actually causes their demise.

I agree that plants in full sun not having their optimal water requirements met are dealing with more stress than those in shade and partial shade.

Becky, there are all sorts of combinations of effects that might be responsible. Looking at your pictures, is there a difference in mulch between the two areas?

It also happens with other plants that seedling resistance and adult plant resistance to rusts can be different, I don't know if that might apply to daylilies.

Like Judy, I also wondered if the leaf trimming might have made some difference. Bear in mind a leaf or part of a leaf can have rust inside that hasn't sporulated (produced spores) yet in which case you can't tell it's there. It does look like in one of your pictures that the leaf tips are affected, I think.

Regarding stress, that's a rather controversial topic. There are some authorities who believe that stress reduces rust rather than increases it. Others say that might only be the case at certain stages of the disease. The logic would be that since rust is one of the few fungal plant diseases that needs living tissue to survive and reproduce, it will do "better" on healthy foliage. Most fungal diseases of plants can also persist on dead and dying foliage but not rusts, smuts or powdery mildews which are considered "obligate parasites". Some daylilies have a reaction to rust that causes the whole or part of a leaf to die. That might make it appear that the plant was more stressed.

It's also possible that your two beds, although fertilized the same, do have different nutrient status (from differences in the native soil), and that can affect rust severity. I wouldn't have thought that would make such a big difference though unless there is a dramatic difference in the nutrient balance.

Edit: forgot to mention, is there a difference in plant spacing between the beds (including non-daylily)? The trimming could also have created more air circulation as well. Another thing again is temperature related resistance genes, if such exist for daylily rust.

Regarding stress and water needs, in my experience and environment, even when optimal water requirements are met in sun-baked heat above 90 degrees, daylilies will undergo much more stress than in shade or partial shade. I'd be interested in learning how, and where, the upper zones divide so that (especially sustained) 90-100 degree temperatures do or don't result in high stress to daylilies, and to see information and pictures that document growing conditions (soil type, humidity, watering styles, etc) and show the difference in results between those environments. Perhaps, also, whether there are differences in practice between commercial (or commercial grade) applications and practices that impact results (spraying, use of chemical treatments, etc.). Whatever ways that rust may be helped or impeded by temperature, environmental or gardening impacts, including trimming, I think there are different results that follow climate/temperature conditions (as there are from cold-stresses in the the lower temps of northern zones).

Focusing of hot temperature impacts, we recently had a heat-wave averaging 105-degrees over three days. Prior to the heat wave, the plant and foliage health in three distinct areas were the same in terms of level of green, and with budding and blooming at comparable rates, soil moisture equally robust within half to an inch of the topsoil, and with only incidental size differences as distinguishing features between foliage and blooms.

Quickly after the heat wave passed, the full sun beds were filled with scorched and highly stressed daylilies (the same as I see every summer once the heat fully commences), while partial shade and deeper shade plants remained unaffected. After doing extensive digging and relocating of daylilies last fall I also learned that after the usual three months at extremely high temps, with as much hydration in the soil as possible during the season, most of the daylilies in beds with full sun exposure had retrograded to a level of juvenile development that required support in a sheltered greenhouse over winter in order to rebound. They are still not back to full-size yet, in terms of foliage and root systems, nor have they flowered this year.

Here are pictures from just after the current heat wave. Again, soil moisture was comparable, as was health, vigor, budding/flowering, etc., immediately prior to the change in temperature, and full sun beds were given supplemental watering as needed during those days.

Deep and partial shade areas:


Full sun beds:

I find there is a definite difference between summer and the cooler months with rust. It likes the warmer times. Even in wet winters, water does not seem to make a difference. Temperature.

My experience is that rust buckets are rust buckets in the shade or the sun. Same with air circulation, a rust bucket in splendid isolation with max air circulation is still an excellent rust bucket.

Unfortunately, some of my favourite daylilies are rust buckets. I trim and burn the leaves now. But I also spray which has made an excellent difference. But I will give it another season to see how I feel about all the spraying.

I suspect the RBs' days might be numbered. There are thousands of daylily cultivars out there that won't need the chemicals. To embrace them seems sensible.

... and with thoughtful cross-breeding between RB's and RR's, with attention and emphasis on RR's and seedling evaluation for performance over time, a helpful variety of genetics is preserved and kept available in the tool kit useful against present and future rust strains. I sometimes find that partially resistant breeding parentage has resulted in sustained and remarkable improvements to resistance in a number of generations of offspring. Just my own take on practical observational information, and my own "secret recipe" for what to cross with what, but similar to what is found in other breeding programs where a super parent may still show some slight lack, but where offspring invariable are found to have picked up a more helpful mix of genes.

If I had to dig up daylilies to pot because they couldn't take heat and full sun, I think I would be turning a critical eye to those cultivars that needed that sort of treatment. I believe that daylilies have their comfort zone. What may be a thriving, robust plant in one zone, may fail miserably in another. If a daylily isn't happy in the zone it is growing in, it needs to live elsewhere. In my case, growing conditions are extreme. Full sun, constant high heat from March to November, no trees, no shade of any kind. If a daylily needs special treatment to grow and thrive here, then it has no place in my garden of 14 raised beds.

I like your proactive approach, Judy! I too am slowly but surely narrowing down those that perform best in the unrelenting heat and sun, just as I think Becky is making thoughtful adjustments to where her's fare best with rust. We are learning so much from each other, with garden environments that may never have received much studious support in the past. It is challenging, yet rewarding, to discover potential ways to accommodate daylily gardens in otherwise inhospitable conditions.

That is why I find sharing info here, as well as in the comments section of a daylily cultivar's database page, is so very helpful, and really appreciated when ATP members take the time to record and help out with their experiences. Performance for heat, sun, shade, rust/conditions, slow or fast increase, strong/floppy scapes, etc., all of those things are so very helpful to everyone, and add such value to the information that will be available in the future to those who want to study or learn from them.