Dear Joe: I don't know what to make of all this new rust disease of daylilies. Some people seem to be overly worried while others seem to think it will be a minor inconvenience. Is this a disease that we should be worried about and what effect may it have on the way we grow daylilies. Should we be doing a preventative spray program or should we wait until the disease hits us. Will it be possible to breed for daylilies that are resistant to this rust disease.
Jack: I wish I could give you some clear answers to all the questions you asked. Unfortunately, there are still a lot of questions that we do not have any answers for, and may not for some time yet. I do believe that it is safe to say that this disease will have some impact on daylilies as we know them today and also impact the daylily society as we know it. A lot will depend on how far and quickly this disease spreads, how severe the disease is and how people respond to this disease.
If you had asked me back in January of this year I might have said that I thought there would be a chance to eradicate this disease before it became a problem. Now, I am believing that this is a disease that we may have to learn to live with. Daylily rust has appeared in a number of states besides the original four states were it was discovered, and it has also been found in landscape daylilies in Florida.
There are several things that need to be considered whenever a new disease or pest makes its appearance. First, is the disease of economic importance? Daylilies may be important to us, but their overall importance is minuscule compared to crops like wheat, corn and other grains and vegetables that make up the bulk of our diets. The loss of daylilies will be missed by those of us who love them, but their removal as a commercial horticultural crop won't have any significant impact on the over all economy. Still, the USDA and various state agriculture departments are currently recognizing daylily rust as a serious disease and that some effort should be made to eradicated or control it.
The next question we need to ask is if the disease can be eradicated, and if so what is the potential for reinfection. To be able to eradicated daylily rust would require isolating the disease when it was first discovered. There are a lot of questions about this rust disease that we do not have answers for, but all indications seem to be that it is a rather aggressive disease and it seems to have spread beyond the point where it can be easily controlled. Eradication at this time isn't impossible, but is becoming more and more difficult as the disease spreads. The initial response to a disease like this, if it is clear the initial intent is to eradicate the disease, is to enact a total embargo on the shipment of daylilies within and out of infected areas which includes a significant buffer surrounding the infected areas. For example, the disease was initially discovered in Florida, Alabama, George and South Carolina. A total embargo on the shipping of daylilies within and out of these states, and a total embargo on the importation of daylilies from South and Central America where the rust disease is believed to have come from, may have significantly impacted hybridizers and growers within these states, but could easily have been justified. Even if it is possible to eradicate this rust disease, the chances are pretty good that it will reappear in the future. Any country that is importing daylilies is going to have to be on a constant vigil for this disease.
If we can not eradicate this rust disease, can we control it? The answer is probably yes, at least in the short term. This is a true rust disease, Puccinia sp., which is an obligate parasite on daylilies. The rust disease reproduces asexually on daylilies, but completes it's sexual cycle on Patrinia, a genus of ornamentals that is not common in the USA. This rust disease seems to be able to survive without its secondary host, which means that it will probably be more difficult to control the disease, but which also means that spray regimes may be developed that will, hopefully, control the disease without it being able to develop resistance through sexual reproduction.
The next question we need to ask is how are gardeners going to react to this disease once it shows up in their gardens? There are probably two extremes while most of us will be in the middle somewhere, at least for the time being. On one side will be the die hard daylily fanatics whose motto will be "spray, spray, spray and then spray some more regardless of the risks." On the other extreme will be those who will compost their daylilies and move on to other plants. Many of us may love daylilies, but we may not like the idea of having to go through the trouble of constantly spraying to keep our plants healthy. My impression is that many AHS members are looking at daylily rust as if it were leaf streak. This is a serious disease that can not be taken lightly.
I suspect that most of us will take a middle, wait and see, ground, and I suspect that our reactions will depend on just how severally this disease does effect daylilies. If this rust can be controlled by simple sanitation and fungicide spraying, then I suspect we won't see many major changes. However, if it becomes apparent that this rust is going to severally effect the health of daylilies or even kill them without a constant spraying program, then I suspect we will see some major changes in the way we hybridize, buy and grow daylilies. The most common approach will probably be to quickly discard those cultivars that are highly susceptible and to look for cultivars that are resistant. It shouldn't take too long to discover which cultivars are susceptible and which are resistant.
The question that many gardeners may have now, especially those with significant financial investments in their daylily collection, is what can they do to limit the chances of daylily rust showing up in their gardens. A preventative fungicide spraying program might at first seem reasonable, but will be of little benefit if there is no rust inoculum to infect the daylilies. I do believe in reasonable and responsible use of chemicals, but I also have to question the repeated use of toxic chemicals in a backyard garden setting in residential neighborhoods, especially when children may be exposed to these chemicals. Personally, I would not recommend a routine preventative spraying program for those at low risk. However, a preventative spraying program may be in order for those who purchased daylilies from growers in infected states who later became infected with rust. Rust spores are spread by wind, so a preventative spraying program may be in order if the disease appears in a garden in your area. Those who do wish to spray their daylilies as a preventative measure would probably be better off using a long term systemic fungicide over a non-systemic fungicide and to alternate between at least two, and preferable three different fungicides.
The most obvious thing to do right now would be to delay the purchase of any daylilies from hybridizers or growers in areas where daylily rust as been detected. If you do purchase daylilies from Florida or any of the other states where daylily rust was originally detected, South Carolina, Alabama and George, then you should grow those daylilies in pots as well isolated from your other daylilies as possible and watch them carefully for any signs of rust. Spraying these plants with a systemic fungicide known to be effective against daylily rust may be in order. You really should grow these daylilies in pots, because, if they do develop rust you will want to quickly and easily dispose of the plant, or move it to another location where you can attempt to treat the infection with as little chance as possible of spreading the disease.
If daylily rust becomes a serious problem, then I can see some major changes in the AHS and in the way daylilies are hybridized and sold. The AHS has a number of problems that are common to amateur based non-profit plant societies, such as high levels of inertia to change, and lack of professional management, besides problems that are unique to the AHS. The total lack of leadership on the part of the AHS in regard to daylily rust is only one indication of the problems facing the AHS. The AHS has grown significantly over the last 20 years, with a few bumps along the way, but has been seeing a slowing down of this growth in the last few years. The question is, how will the AHS respond if there is a significant drop off in membership of three or four thousand, or even more? A discussion of this topic alone could easily occupy an article of its own. Not only is there a total lack of leadership by the AHS in regard to daylily rust, but there isn't even an effective scientific studies committee to keep up to date on daylily rust and to make recommendations or to initiate an educational program.
All of us in the AHS face a dilemma because almost all of the major daylily hybridizing is being done in Florida. The occurrence of rust in Florida and the concentration of hybridizers in Florida provides an opportunity for daylily rust to quickly spread to all the major hybridizers, and if that happens we will be rewriting the history of the AHS and daylily hybridizing. Daylily people on their annual mecca trip to Florida could easily, but unknowingly, spread rust spores from one garden to another. A Florida hybridizer could honestly say he isn't infected with rust today, ship daylilies to all corners of the country, only to discover rust infections tomorrow. If we, as customers, play it safe and not buy any daylilies from Florida hybridizers because of the potential of rust infection, then we may be putting these hybridizers out of business, or at least out of the daylily hybridizing business. On the other hand, if they do get infected they will be prevented from shipping daylilies for a period of time which may also put them out of business or seriously impact them economically. I don't know if anyone will listen, but this should be a wake up call to all of us in the AHS to the fact that we need to diversify daylily hybridizing to a more regional basis and not rely on a limited number of hybridizers all located in basically one area.
Can we hybridize for resistance to daylily rust? The answer is clearly yes, but we face another dilemma - you can't breed for resistance to daylily rust unless you can test your seedlings for rust resistance, which basically means that rust is going to have to be present in your garden, or you will have to artificially inoculate the seedlings. Breeding for disease resistance is no more complicated then breeding for any other traits. You locate sources of resistance, cross them to daylilies with the flower traits you want, and then advance them to future generations selecting out those seedlings that have the beauty you want along with the disease resistance. Selecting for certain flower traits, like spiders or red flowers, is easily because you can visually evaluate the seedlings. However, just because a seedling doesn't develop a disease symptom doesn't mean that it is resistant - it could have luckily escaped being infected. You have to go through the trouble of actually infecting the plant or growing it over a period of time in an environment where the disease is present. I'm sure, if daylily rust does spread through out the country and is a severe enough disease to require breeding in resistance to rust, that we will in fact develop rust resistant daylilies, but it will come with a significant price tag. It's going to take a significant amount of time to bred in rust resistance and combine that with the beauty we expect.