About daylily rust.

How cold must the temperature be and for how long to kill the rust?

Thanks.

Third Q and A down on this page, but basically to be safe you need for it to get cold enough for all the foliage on all the daylilies to be killed down to the ground all at the same time for an as yet undetermined period of time. Cold alone does not kill daylily rust spores, and the fungal body inside the leaves may be able to survive the same temperature that the leaves can survive. That's going to vary by cultivar and probably local climate.

http://web.ncf.ca/ah748/FAQ.ht...

The cold doesn't kill the spores, the lack of a living host does.

There's two ways... wait till the foliage dies back to the crown, Or cut the foliage to the crown.

Cutting to the crown wouldn't be possible for established plants growing in the ground though, because the crown is usually beneath the soil surface. Cutting the leaves a bit above the soil surface may not get rid of the rust unless the remainder of the leaves are killed by cold - cutting infected leaves causes spores to fall down between the leaf stumps where they could infect, and also pustules can exist not very far up from the crown.

It's not likely that the rust would winter over in Gerry's zone unless there were some specific circumstances, like possibly a heavy winter mulch that allows some leaf bases to stay green. Or maybe a very heavy winter snow before the plants have frozen back and which remains all winter. Those last two are speculation though, not something that we know happens for sure. A greenhouse would be risky though.

@Sooby Instead of cutting the leaves to as close as possible to the crown, would ripping all the leaves off (as close as possible to the crown) be better, especially for true evergreen cultivars?

admmad said: Sooby Instead of cutting the leaves to as close as possible to the crown, would ripping all the leaves off (as close as possible to the crown) be better, especially for true evergreen cultivars?

If they would rip off cleanly then yes, but since they don't detach easily unless they are senescing I don't think so. If you look at this page, when I tried this the outer leaves would pull off cleanly but as I progressed to the inner ones they started to break off.

http://web.ncf.ca/ah748/newpla...

They still may have broken off close enough to the crown that it wouldn't be a problem, but this was with a plant out of the ground. If it was in the ground you wouldn't be able to pull sideways like that. If the plants are evergreen they may put up new growth if it is warm enough before any dislodged spores have been de-activated by the environment, too.

How about digging the earth away from the crown and cutting all the greenery down to very near the crown. I am sure it would not be a 100% cure, but I am asking if it would have a significant deterrent effect?
I don't remember why but I always thought it would be good to spray the daylily foliage with a fungicide then cut it back, but then I read you should cut it back then spray. Which is actually best or does it matter?

I had a row of seedlings mixed with a few named cultivars along my back fence. The temps are finally getting below freezing supposedly tonight. So I went ahead and cut all of the foliage off all those plants down at ground level or below (all except one that showed no rust-the rest did show some signs of rust). So I will wait and see next year if it has any affect on them. Some of them were real rust buckets last year.
I also had a row of named cultivars mostly with a few NOIDs in my rose bed, I cut them all back about a month ago and now they already have new pristine looking green foliage growing back. I will be interested in seeing how they fair next year. The named varieties were new this year and some of them are known to have a rust problem so I thought it worth a try with them.

The idea with the double fungicide treatment (before cutting, wait a few days, then spray the cut stumps) as opposed to fungicide treatment after cutting was to reduce the number of live spores in the environment, having been disturbed and become airborne from the cutting. It was suggested to me by a plant pathologist that a single treatment after cutting may be sufficient but it would depend on the fungicide also. The cut stumps would get better fungicide coverage. I don't think it has ever been investigated scientifically which might be better. It would also depend on the fungicides used. Since a soil drench with azoxystrobin (Heritage) was effective for a prolonged period of time, I wonder if that would be a viable alternative.

Whether cutting back (without spraying) as you described would work would likely depend on how long it takes before new growth emerges that could encounter spores that are still alive on the cut stumps.

Thank you for all your inputs. It looks like this is a subject that needs a lot more experimentation and research. I have read that rust does not survive the cold winter, but some of you indicate otherwise.

I need more time to observe my plants and try different methods of dealing with rust. I did spray some and more will be sprayed. I am always concerned about new arrivals. They arrive when I am most busy and I do not spray them immediately.

Would it be worthwhile to spray the soil when preparing for new arrivals?

I guess it depends on what you consider a "cold" winter. The general rule of thumb is that daylily rust may survive the winter in Zone 7 or it may not, depending on the location and the conditions that winter. Warmer than that, i.e. Zone 8 and warmer, it likely will survive. In zone 6 and colder zone it won't normally survive. It definitely doesn't survive here in Zone 4 because I've twice introduced it to experiment with. In other experiments it did not survive in Ohio, nor did it persist without Patrinia in a relatively mild winter in Japan where the daylilies were deciduous.

If your daylilies all die back to the ground for the winter then it cannot survive without the presence of the alternate host, Patrinia spp. because rust diseases need a living host. The "winter spores", the black teliospores, that form towards the end of the season can survive on dead daylily tissue but cannot re-infect daylilies in the absence of Patrinia to re-start the process. In zone 5 you shouldn't have rust overwinter.

I don't see that spraying the soil when preparing for new arrivals would be worthwhile. It would be the new arrivals that bring in the rust.

I'm in zone 5b and rust was introduced to my daylilies for the first time this year. I have it in all areas of the yard. If there is anything I can do to prevent it coming back in the Spring I would love to do that. I haven't removed the leaves yet, some are still green because of our mild Fall, and am wondering first, if when I remove the foliage if disposing of it in our timber away from the daylilies would be ok, and also if I should treat with a fungicide this Fall or in the Spring. I am supposed to be on our local garden tour next June and really don't want the rust showing up again. Thanks for any advice!

Ginny, if all your daylilies typically die back completely for the winter, which I assume they do in Zone 5, you don't need to do anything. If you think any infected daylilies may stay green through the winter then you could cut back and treat with a fungicide. It's much more likely that you would bring it in again if you buy new plants from an infected garden next spring. I'm assuming that you don't grow any Patrinia plants because that is how daylily rust persists in very cold climates like Siberia. If there's no Patrinia then it would be safe to dump any cut foliage in your timber area assuming you don't have any daylilies that stay green through winter. You wouldn't want to do that if there are any Patrinia plants nearby or if your daylilies stay green.

Not sure what a Patrinia plant is so I assume I don't. Yes, my daylilies completely die back in the winter in normal years and assume this will be no different even though we are just now getting freezing temps.

Patrinia is not native to North America and you (or someone nearby) would have to have deliberately planted it.

In that case I'm good - thank you.

profesora said:Thank you for all your inputs. It looks like this is a subject that needs a lot more experimentation and research. I have read that rust does not survive the cold winter, but some of you indicate otherwise.

I need more time to observe my plants and try different methods of dealing with rust. I did spray some and more will be sprayed. I am always concerned about new arrivals. They arrive when I am most busy and I do not spray them immediately.

Would it be worthwhile to spray the soil when preparing for new arrivals?

It's not the cold function that kills the viable spores, as it will overwinter on patrina.

For us its the function of our plants losing all their living foliage. So in these colder zones 7 and so and down, when the plant goes Dormant or the SEV/EV's die back to crown the rust spores no longer have a viable host in which to live.


If rust does concern you... as it does me since I operate a heated greenhouse year round now... You can read this blog entry of mine which I go into some detail on the products I have used, and continue to use to combat rust.

http://northerngreenhouse.blog...


I see someone mentioned using heritage as a drench. As this is a MOA for Azoxystrobin but unless you only have 5 or 10 plants I would use it as a foliar spray since it will be far more effective and cost effective.

I am a bit confused.
Aren't there three different aspects of daylily rust that are of possible concern?
1) The spores that can survive winter, the black teliospores, cannot directly infect daylilies. They are not a concern unless they infect Patrinia.
2) The spores that cannot survive winter, the urediniospores, can infect daylilies. However, they presumably are killed either by low temperatures or other environmental factors?
3) The actual rust growing inside daylily leaves, the mycelium. If all the infected daylily leaves die then the mycelium also dies. Is that correct? If infected leaves do not die then is there a temperature at which daylily leaf tissue survives but mycelium within the tissue dies?

I don't think there is a temperature which will kill the rust and not kill the leaves themselves.

Peter, daylily rust doesn't overwinter on Patrinia, it overwinters as teliospores, the black winter spores, (not the orange summer spores except in very mild winter climates) on dead daylily leaves and then transfers to Patrinia in spring. Of course an existing infection can also overwinter as mycelium (fungal threads) inside any daylily leaves that can stay green and alive.

The spores are are just the reproductive units, like a plant seed, the actual fungal body itself lives inside the leaves feeding on nutrients from the plant's internal cells.

Heritage as a soil drench was found to control daylily rust for 120 days with a single application, a result that was comparable to 14-day interval foliar sprays, see Dong et al, 2013 : http://apsjournals.apsnet.org/...

Maurice, yes to 1 although technically it is not the teliospores themselves that affect Patrinia but their next spore stage but it amounts to the same thing.

For 2, daylily rust urediospores (the orange ones) can be deep frozen for use in lab tests at temperatures far colder than would occur in nature. So it is not cold alone that kills them outdoors but some combination possibly combining time, light intensity, moisture and temperature.

For 3 yes if the infected leaf dies, the mycelium inside it (the body of the fungus) dies too. In some rusts the mycelium can be killed by temperatures above that which would kill the leaves but nobody has tested this for daylily rust. So to be safe we assume that the leaves need to actually be killed to kill the rust. It is possible that the fungus could be killed a little before the temperature goes low enough to kill the leaf.