presentation by Dr. Nameth
notes by Rebecca Board

At the 2002 Region 2 Winter Symposium in Cleveland Ohio, Dr Nameth gave a presentation on the research being done on Daylily Rust at Ohio State University. An audio tape recorded the presentation, and these are the notes I made from that tape. These are my notes, not the speaker's notes and not a transcription. I have not yet been able to view the slides and had to guess a bit as to what was shown. If you think you see an error, it is quite likely mine and not the speaker's.

Introduction

• There's lots we don't know - still more questions than answers.
• Rusts are found all over the world, and there are thousands of different kinds.
• Other rusts are an economic problem, some affect food crops.
• The problem is much less serious from a pathologists perspective than that of a daylily collector or grower.
• A lot of what is said is based on work with other rusts.
• Other rusts have been worse, and are now controlled though not eliminated.
• Geranium rust will shut down down a nursery, but it is now quite rare and there are effective ways to control and eliminate it.
• A major rust epidemic threatened wheat in 1930's and 40's, but the USDA stepped in, established drastic controls, and now the problem is controlled though not eliminated.

• All three of the following are necessary for disease.
  • Pathogen
  • Susceptible Host
  • Favorable Environment
• A rust spore on a daylily leaf will not infect if conditions are not favorable.
• In the greenhouse, keeping leaves as dry as possible can prevent favorable conditions, though this is obviously not an option outdoors.
• Probably less rust in Arizona and Utah and more in the South due to rainfall.
• We're going to have to use chemicals at this time to create an unfavorable environment to control rust.
• We could, theoretically, eliminate daylily rust by eliminating the susceptible host -- ALL the daylilies.
• Long term, we can breed for resistance, as was done to solve the wheat crisis.

• [RRB - Since I son't have slides, Sue suggested this page from the Cereal Disease Laboratory for images of wheat rust as well as more information. http://www.crl.umn.edu/posters/2001/KJL/stem_rust.html.]
• Slide shown of wheat leaf with both teliospores and urediospores.
• Formation of teliospores on wheat triggered by falling temperatures and shorter days.
• The teliospores are thick walled and designed to survive winter.
• In the spring, the teliospores start the cycle which infects the alternate host, barberry.
• [RRB - More of life cycle was described, but I'm not even going to try. See Sue's daylily rust life cycle page for these types of details.]
• At one time, the US pulled out and removed barberry in an attempt to control wheat rust. It failed because spores blew back in from Mexico on the jet stream.
• Only urediospores are needed to form disease cycle - the rest of the life cycle really isn't considered a disease.
• Urediospores can travel 1000's of miles in jet stream (which has been measured by taking air samples using aircraft), so speculation that daylily rust can travel 5 miles on the wind is easy.

• Slide shown of black teliospores and orange urediospores on roses. No one in audience claimed to have seen anything similar on their daylily foliage. [RRB - I wish I had the slide, but you can view both kinds of spores on daylilies at Sue's Daylily Rust in Japan page.]
• Production of black teliospores triggered by cooler temperatures and shorter days.
• Teliospores on roses are rare in California where climate isn't suitable for triggering their formation.

• Daylily rust is a puccinia.
• It is a heteroecious rust, meaning it has more than one host.
• It is on the alternate host that the daylily rust sexual stage takes place.
• Severity varies with daylily cultivar. This is a variation in resistance, but not total immunity.
• Rust mass grows below outer layer/cuticle, then blister forms below the skin. The pustule ruptures through the epidermis to release the powdery spores.
• Plant veins tend to constrain fungal growth and make streaks.
• Heteroecious rusts produces 5 kinds of spores, but we really only have to worry about 2 of them.
• The orange urediospores have thin walls. They are only designed to spread rust in the summer months.
• Teliospores have thick walls and exist to survive the winter months, but they don't infect daylilies.
• Rust urediospores need 4-5 hours of moisture for germination. Dew would be enough if it stayed on the leaves that long. Rainy overcast days will be the worst.
• Best germination will occur when temperatures are in the 70's. It will happen below 70F and above 90F, but slowly.
• Rust germ tube penetrates tissue or grows on top until it finds an opening like a stoma.
• Rust usually grows between the cells, but sometimes it enters inside an individual cell.
• You can't grow rust in a petri dish [in agar]. It may germinate, but will not carry out it's life and disease cycle

• There are still many questions about the alternate host(s).
• We don't know if it synonymous with hosta rust.
• Don't know how snow cover affects winter survival.
• Mild winter in Ohio this year, which will affect results.

• We need more science based information - Dr Nameth doesn't claim to be either a rust or a daylily expert.
• Rust spores are like seeds. They can survive for a length of time, but require favorable conditions to germinate.
• Rust mycelium requires living tissue to grow and reproduce. It won't live in dead tissue very long.
• The urediospores' thin walls make them more vulnerable to heat, desiccation, microbes, and fungicides.
• We are going to have to use chemicals to get a handle on this right now.
• As daylily growers, we need to start carrying a hand lens into the garden to examine foliage and pest problems, looking for rust at the early stages. A cheap 5-10X lens is sufficient. We need to get up-close and personal to tell it from other pests.
• Slide shown of an edema - a calloused leaf area - another example of something that is not rust but easily mistaken for it.
• Can take cuttings of suspicious leaves and place in a jar with some moisture (moist chamber) to observe development of spores more quickly, probably 3-4 days.
• The disease cycle is different than the life cycle. We don't need the sexual stage for the disease. Eliminating the sexual cycle does not eliminate the disease. But not having a sexual stage is bad for the rust.
• Many different fungi are "imperfect forms" - meaning they don't ever produce a sexual state in nature, though sometimes the sexual stage is seen in a laboratory.
• Rust is easier to deal with if there is no sexual cycle - in part because the urediospores are more vulnerable.
• Dr Nameth says he has yet to see teliospores in Ohio in any sample brought to him. (If you see them, he wants to know!)
• If teliospores are not forming in Ohio, then it's because conditions are not right for them to form.
• The daylily rust infection is expected to stay in the leaves and not infect crown or roots. (Viruses infect the entire plant, most rusts do not.)
• Urediospores are not overwintering in Ohio - they do not remain viable, even with mild winter.
• HOWEVER, rust will definitely be able to overwinter as mycelium growing inside living leaves even though no spores are seen.
• The hyphae growing inside the leaves will not grow down into crown or dormant buds.
• The 'systemic' fungicides are not true systemics as we think of with pesticides. Rather, they are localized systemics which may move a few inches along the treated plant leaf. They offer no protection to new growth since treatment.
• Contact fungicides kill spores and apply a protective barrier to the sprayed leaf surface.

• Spores left outside on cut leaves, left on bare ground and exposed to elements and microbial action, were harvested and brought into the greenhouse to germinate. These spores were unable to cause infection since early December. (No zone extrapolation was made based on these measurements.)
• Some spores were able to generate germ tubes after exposure, but were not able to live and grow long enough to cause infection.
• Plants treated with exposed spores were left much longer than normal cycle to make sure infection was not merely delayed.
• Fungicide trials will be conducted in the spring.

• No quarantines now, and Dr Nameth does not expect to see them this spring.
• In response to a repeated question about overwintering urediospores, Dr Nameth said to forget about spores overwintering. Mycelium is the big concern, though it is possible it is less resistant to cold than the leaf.
• If you trim and overwinter in cold climate -- your daylilies should come up clean.
• We're going to have to start looking at daylilies like roses, and spray weekly.

• Don't grow daylilies and patrinia together.
• Clean up everything in the fall - remove dead dormant foliage and trim evergreens.
• Burn or compost rusty leaves. Heat and microbes will kill any urediospores.
• Watch the evergreens early and closely in spring, and get on them with fungicide early.
• Mix and match protectant and systemic fungicides.
• Wait for 60F degree days to spray plants as both fungus and plants grow slowly when colder.
• Recommends using contact fungicides after you see spores, and use systemics as preventative spray. This was hotly disputed by certain Florida folks who felt contacts were needed as part of preventative program.
• Recommends preparing incoming plants by cutting back foliage and treating with a disinfectant dip (Zerotol, 10% bleach).

--Rebecca, 3/12/02, last modified 3/15/02

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