Last updated 10/25/07.
The idea of this FAQ is to give a quick overview, to fill the gaps that the FACTUAL pages leave, to debunk the nonsense, and refer people to the factual pages. I will try to keep it up to date as new information becomes available and as people suggest new questions. I pretend to no special expertise in plant pathology, but do attempt to keep abreast of developments in daylily rust. I intend for this FAQ to be primarily fact based, but there are places where I offer my opinion. I attempt to identify those places, and will gladly rectify any omissions.
This FAQ is written primarily for AHS members and not commercial growers, though it may prove useful for all concerned.
If you haven't had a basic course in plant pathology, I highly recommend this very brief introduction to plant pathology concepts and practice: Plant Disease And Plant Disease Diagnosis (http://scarab.msu.montana.edu/Diagnostics/DiseaseDiag.htm).
The few technical terms used in this FAQ can generally be found in this Illustrated Glossary Of Plant Pathology (http://www.apsnet.org/education/IllustratedGlossary/top.htm).
This FAQ is divided into 6 sections:
Sue Bergeron's Daylily Rust Information Page (http://www.ncf.ca/~ah748/rust.html) is THE one web page to bookmark on this subject.
The stage of greatest concern to us now, as daylily growers, is the stage that infects and reinfects daylilies through cloned spores called urediniospores. These can be spread by wind, splash, contact, and animal (or human) transport. When they arrive on a leaf, under the right conditions of temperature and humidity they will germinate and attempt to grow through a stomate to infect the interior tissues of the leaf. When enough growth has been achieved inside the leaf, and environmental conditions are right, the rust fungus produces pustules that burst through the surface of the leaf to release a new generation of cloned spores.
This rust has spread long distances between gardens and growers primarily by shipping of infected plants. There are a few reports of infections that might have arisen otherwise, but the vast majority of infections are directly attributable to receipt of a plant that seems to have borne the infection. It seems very unlikely that these infections have been spread long distances by wind: that only seems to happen with crops that cover large amounts of land.
A report of frequent spread by wind (presumably) over indeterminate distances (probably up to a few miles) to at least 30 non-AHS gardens in Florida has come in from Dave Talbott. Infected plantings create "spore pressure": the presence of spores in the atmosphere. Spore pressure declines with the square of the distance, and the lower the spore pressure, the less the probability of infection. As more reservoirs of infection develop in overwintering areas, the spore pressure will increase, and we'll see more local transmission by wind. Long distance transmission by wind of daylily rust has not yet been shown to be likely.
Within a garden or field, rust is HIGHLY CONTAGIOUS. Wind, splash, contact, and animal transport can spread rust spores throughout a garden, infecting it thoroughly in a very brief period.
Daylily rust is not thought to be systemic. In individual fans, rust seems to pass from leaf to leaf by infection by spores alone. Not by growing though the tissues of the crown. It is not clear yet how far infections in leaves grow.
These symptoms and signs are well illustrated at the Daylily Rust Information Page.
An additional factor is that rust is conspicuously ugly on many daylilies, perhaps much worse than leaf streak.
A secondary reason is that controlling rust requires expensive and time consuming application of fungicides, comparable to the labors of Rosarians (rose fanciers). There are reports that controlling for rust adds 20% to the costs of commercially growing a daylily. And while the fungicides involved are more benign than many other pesticides, they still present a risk that it would be better to forgo.
The question boils down to whether you want to avoid unnecessary diseases enough to attempt to avoid rust. Most people who have rust wish they never had it.
All daylilies seem to be susceptible to rust, as opposed to resistant to rust. Resistance means relative difficulty for infection to occur. No resistance has been reliably reported yet in daylilies.
The variation that Matthew and others report is properly described as tolerant versus sensitive. A tolerant plant will have the disease, but not be much affected by it. A sensitive plant will be severely affected by the same disease.
Rebecca Board's Rust Survey is attempting to survey tolerance across many gardens. This should help a great deal as the data starts to flow in.
The good news for breeders, according to Matthew Kaskel, is that it seems to be very easy to screen large numbers of seedlings for tolerance at a very early stage. This doesn't imply that they will exhibit tolerance under all conditions, but it does allow one to screen out seedlings that are highly sensitive under the grower's conditions.
In the north, tolerance my not be as important as dormancy. If dormant daylilies can shed the infection with their leaves, gardens would be able to start the year free of infection. In areas of sufficiently severe winter, it's possible that even evergreens might be able to shed the infection. We'll learn more about this possibility in 2002.
I'll be happy to link here to recent recommendations for spray programs when I see them on the web.
But a brief, general outline was presented by Dr. Williams-Woodward at the Sept. 2001 Region 15 fall meeting:
"Cutting back infected leaves to the ground and removing from the garden is recommended to reduce the number of spores present, remove most of the infected but not yet fully mature infections, and remove most of the green surface needed for germination. Plants will need to be sprayed as they grow out to finish the last remaining infections and prevent the remaining spores from germinating."
"Rust should be unable to survive a cold winter if the plants are _completely_ dormant, showing no green anywhere, and if there is no alternate host present. This is based on the experience of only one winter (a cold one) in the speaker's own garden with only dormant varieties."
"It was recommended to cut and remove all foliage from the garden in the fall, and possibly to continue to cut back evergreens during the winter months to reduce the odds of rust surviving the winter. The more foliage is removed on new arrivals, the less chance of rust, though obviously one cannot reduce the odds to 0 without killing the plant."
[One further note of explanation here: when removing possibly infected foliage, care should be taken to avoid later airborn distribution of spores from the cut foliage. It could be bagged, burned, or buried, for example.]
Pat Stamile posted an excellent explanation of the recommendations for northern gardens to the email robin, available here.
Dave Talbott has passed along an outline of his current (2002) spray
program for his commercial garden. It is here for illustration only,
not recommendation. Home gardeners may not need such a thorough
program, as they may prefer to merely control rust.
We are back on a weekly spray program now that the weather is moderating. High 20's,low 30's and upper 40's are not conducive to pustule production and we only spray bi-weekly during the winter months. This is my schedule which has kept me asymptomatic for 2001 and into 2002. On a weekly basis I spray alternately with:
Chlorothalonil (Daconil Ultrex)
Triadimefon (Strike 50 or Bayleton)
Mancozeb (Dithane or Fore).
I spray plants to run-off and use a spreader sticker. Although it may be overkill for the homeowner but several times a season I will substitute Azoxystrobin (Heritage) for Triadimefon.There is a cheaper form of this material named Abound. However it has only 20% of the active ingredient rather than the 50% of Heritage. We dip each plant in mancozeb and let it dry before shipment.We know the precise dosage to use with this material to kill spores. We do not know with clorox.
Bothrotes canaliculatus, a Tenebrionid beetle that feeds on fungi, has recently been reported feeding on rust spores, but they are unlikely to eat a significant amount of rust.
This is a hotly debated subject. The current wide distribution of rust within AHS gardens is primarily due to popular central Florida hybridizers who did not shut down their sales, in my opinion. AHS members were poorly informed of the threat and its significance; the Florida hybridizers had serious conflicts of interest in publicizing this menace, and the AHS did not publish any information to the members until long after the shipping season.
If you have had rust in your garden, there is a significant chance that you might sell some plants with rust. Even if you have clean looking plants, even if you have been spraying diligently, the plants might well have concealed infections that will be revealed in as long as three to five months after leaving your garden. There have been numerous reports of this happening with plants from the Florida hybridizers in 2001. It is possible that the latest spray regimes and sanitary practices at these growers have freed their plants of rust, but unfortunately there is no easy way to test this in advance. No major grower that I know of is even attempting to test this adequately. In 2002, this problem may be continent-wide, depending on how well rust overwinters.
If you are selling to gardens that have rust control practices in operation, either quarantine or spraying, this should not be a problem.
In short, the major ethical dilemma is whether the customer understands and is willing to accept the risk of purchasing from your garden. Seller's responses to this dilemma have ranged from shutting down sales entirely (at least two popular Florida hybridizers did this) to stonewalling and downplaying the issue while continuing to sell freely. My opinion is that at the very least, customers should be informed of your garden's rust situation and control practices.
Tolerant plants thus produced might act as Typhoid Mary's, carrying hidden infections with them. However, here as in other crops, tissue culture can rescue these varieties from infection far more certainly than current fungicides. The cultured plantlets could then be grown to maturity in clean, isolated fields. Similar techniques are used for many commercial crops.
It may be necessary to outcross to rust tolerant plants from other breeding programs, if yours doesn't happen to have enough tolerant varieties.
Alternatively, seed produced from rusty plants can be surface sterilized with dilute bleach or hydrogen peroxide, and germinated free from rust. Then the seedlings can be grown in a garden free of rust. Pollen from rusty plants should also be safe, especially if cut buds are surface sterilized before they open.
Another extended discussion of breeding for tolerance is presented by Dr. Raoul A Robinson at his Return To Resistance web site. A short (but technical) summary of his methodology is: The Acceptance of Horizontal Resistance in Crops.
None of these guarantees you'll avoid rust, but they all improve your chances of avoidance.
There is a conflict of interest between sellers who have had rust and buyers who might wish to avoid rust. If a seller provides information about the rust situation, it might deter a sale, and few small businessmen want to risk their business that way. Several noted daylily growers have told me this explicitly. None of them want to send a rusty plant, but none of them want to be shut down by agriculture departments, lose business, or be sued because they implied their plants were rust free. Thus relatively few mention rust in their catalogs. All that I've asked have responded to direct inquiries.
Despite vigorous spray programs, many central Florida sellers who had rust in their gardens sent out rusty plants in 2001. Some of the plants showed no signs of rust until as much as 3 to 5 months later, and then developed obvious infections almost overnight. There is no way yet to be sure that plants are rust free while spraying them to control rust, though they might be less likely to be infected if they are from a garden which never had an outbreak. There is no certain security.
In 2002, you might be able to purchase rusty plants from almost any state, because the disease has been introduced nationwide to many sellers.
Nor are mass market sources or ordinary nurseries safe. There were many reports in 2001 of rusty plants available for sale at WalMart and other sources.
Pat Stamile has contributed this advice:
This procedure is pictured by Susan Bergeron here.
This year, the New England Daylily Society is limiting its spring sale
and auction to "companion plants" (horrible term!). The membership has
concluded that we'd like to be careful, and not sell our own plants until
we know more about the rust status of the source gardens, and know more
about how well rust overwinters here. We expect to then reconsider for
our normal August auction.
If rust infections in the north prove to be tender, and easily
eradicated by winter and dormancy, then a strategy of buying after
the northern bloom season would minimize rust problems.
If there are any plants you are unsure of I would break off the outer two or three leaves right down to the crown. Leave no bits of these outer leaves. Cut the remaining foliage down to 1-2 inches and dip the plant in Daconil. If Daconil is not available use a 10% bleach solution or a solution of 2 oz. of Zerotol in one gallon of water. The scapes and plants will be smaller than normal but you should be able to avoid rust. Do not just cut the plants back and dip without removing the outer leaves. Dr. WW reported that she saw spores and pustules on these outer leaves which were only one half inch above the crown. Remember no treatment I know of can remove rust once it is inside of the plant which is why you especially need to remove these leaves and cut back the plants.
Pat Stamile has contributed this advice:
This procedure is pictured by Susan Bergeron here.
This year, the New England Daylily Society is limiting its spring sale and auction to "companion plants" (horrible term!). The membership has concluded that we'd like to be careful, and not sell our own plants until we know more about the rust status of the source gardens, and know more about how well rust overwinters here. We expect to then reconsider for our normal August auction.
If rust infections in the north prove to be tender, and easily eradicated by winter and dormancy, then a strategy of buying after the northern bloom season would minimize rust problems.
The Brooklyn Botanical Garden booklet on Natural Disease Control has a good summary in the chapter Least-Toxic Controls of Plant Diseases.
You can't fill factual gaps with facts: you have to fill them with statements of what is not yet known. That way people know that they don't need to search for the information, and they also know where they can contribute new information.
An excellent example and explanation of phenology is at the Daylily Spring Sickness Phenology Page.
To the best of my knowledge, phenological information on this rust has been essentially undocumented in the USA, and never assembled. Because of the huge range of climates, phenology might require very different indicators in different regions. This would be a nice project for somebody, and the results could be placed in this FAQ.
A note of caution here: there are already reports in 2002 of northern growers overwintering rust on plants grown in greenhouses. It seems likely that the infection could escape to plants grown outdoors.
These are not approved for any use in the USA or Canada, and that situation is not likely to change because of daylilies. It should be possible for these to be tested by US researchers.
Francois also writes about non-systemics:
At MWS, BAS 500 was said to be the most effective fungicide, better than the often heralded HERITAGE. It was also announced that BASF (the makers of BAS 500) were almost ready to introduce INSIGNIA, a spray based on BAS 500, tested on ornamentals and to be applied with intervals of about 1 month.
has adopted the following scale:
Poor: The plants are covered in rust pustules and are highly disfigured and noticeable even at some distance.
Fair: The plants are covered in rust pustules and are somewhat disfigured when viewed at short range.
Good: The plants have many pustules, but their presence is only offensive on close examination.
Excellent: The plants have very few pustules, and/or their presence is only noticeable on very careful examination.
Matthew Kaskell has provided a more extensive description of how the
most tolerant plants differ from more susceptible plants:
These are plants in which only the outermost leaves are infested with pustules, and there are very few pustules actually present. The pustules are mostly confined to the very ends of the foliage and along the margins of these oldest leaves. Also, there is not much tissue damage to the affected leaf and there is very little "yellowing". The pustules are on what otherwise appears to be a fairly normal and apparently healthy leaf. But the most important COSMETIC attribute that I have found to be shared by the most attractive clumps is that they all have arching, healthy-looking, unbroken foliage with the tips of each leave pointing "down". And these leaf tips are usually buried within the foliage mass, with their rust damage discreetly concealed from public view. The foliage, except at the very tips, is clean and free of pustules. Except under the closest inspection, these clumps APPEAR free of rust damage.
The Kaskell observations may be only one of many forms of rust tolerance: we should be on the lookout for others. For example, if a period of dormancy can eliminate rust, that is a mechanism of tolerance.
Judging rust tolerance across more than one location might be much more difficult: environment and plant behavior my vary significantly, and cause different susceptibility to rust.
In short, there is no good scale yet. Whatever scale is developed should be calibrated in each garden against some common varieties: perhaps widely grown Stout medal winners such as STELLA DE ORO and STRAWBERRY CANDY. The calibration will help to compensate for differences between gardens and measurers.
I'm deeply in debt to Dr. Williams-Woodward and Susan Bergeron for much information, fact checking, and miscellaneous advice. Errors, omissions, and ungraceful statements are doubtless my fault. I'm also grateful for contributions from (in no particular order) Matthew Kaskell, Dave Talbott, Pat Stamile, Francois Verhaert, Darrel Apps, Rebecca Board, Mike Derrow, and perhaps others whom I've clumsily forgotten. Remind me, and they'll be included.
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