Continuing Education and
Communication Services
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
8/13/01
Contacts:
Mark Gleason, Extension Plant Pathology, (515) 294-0579, mgleason@iastate.edu
Del Marks, Continuing Education and Communication Services, (515) 294-9807,
delmarks@iastate.edu
Yard and Garden Column for the Week Beginning Aug. 17
Daylily Rust -- It’s Here
By Mark Gleason
Extension Plant Pathologist
Iowa State University Extension
If you grow daylilies (Hemerocallis) in Iowa, your life just got
a bit more interesting. Daylily rust, caused by the fungus Puccinia
hemerocallidis, was found this past week on daylilies in West Liberty
and Atalissa in eastern Iowa. In both cases, the source of the rust was
plants shipped from a Florida nursery.
The appearance of a new disease always sets off wild excitement (OK, mild excitement) among plant pathologists. But why should you care about daylily rust? The reason is that this rust could turn out to be a serious problem for daylily growers.
Consider a few factoids about daylily rust. It’s a newcomer to the
U.S., having been spotted first in a daylily nursery in the southeastern
U.S. about a year ago. Since then, the disease has hitchhiked on nursery
stock to nurseries and landscapes in Alabama, California, Florida, Georgia,
Indiana, Minnesota, Kansas, Kentucky, Louisiana, Maryland, Mississippi,
Missouri, North Carolina, South Carolina, Tennessee, Texas and Wisconsin.
And now, add Iowa to the list.
What does it look like? The most obvious symptoms of daylily rust are
yellow to brown streaks on the leaves. As you get closer, you’ll
see numerous small, orange to yellow spots that poke out of the leaf surface;
these are called pustules. The pustules soon pop open and release innumerable
dusty, orange-colored spores. When you rub the pustules gently with your
finger, or against a white piece of paper, the spores leave an orange
streak. The orange pustules and spores are the distinctive symptoms of
daylily rust. As symptoms progress, leaves turn yellow and dry up.
It’s easy to confuse daylily rust with a couple of look-alike problems
on Iowa daylilies. Daylily leaf streak, caused by the fungus Aureobasidium
macrostictum, also causes brown to yellow leaf streaks, but no orange
pustules. Aphid feeding damage can look similar too, but again there are
no pustules. So if rubbing leaves produces a dusty orange deposit, it’s
rust.
Rust won’t kill daylilies, but it will make them ugly. The most
worrisome part of the story is that the daylily rust fungus is very good
at spreading itself around. Thanks to infected nursery stock, daylily
rust already has jumping-off points in many states. Once in a nursery
or landscape bed, infected plants can quickly churn out vast quantities
of spores, which can spread on wind currents for long distances. It takes
only one rust spore to infect a plant.
Many varieties of daylily are susceptible, including Stella de Oro, Pardon
Me, Gertrude Condon, Starstruck, Joan Senior, Colonel Scarborough, Crystal
Tide, Imperial Guard, Double Buttercup and Attribution. The list is bound
to grow rapidly as the disease spreads. The good news is that some varieties
appear to be resistant, at least partially. But a list of resistant cultivars
hasn’t been developed yet.
Where did this orange menace come from? Until last year, the fungus was
reported only from Asia (also the ancestral home of all daylilies). Fingers
have been pointed at nurseries in Costa Rica as sources of rust-infested
daylily crowns shipped to a Georgia nursery. But so far the rust has not
been observed in Costa Rica.
If our shores are being swarmed by rust-infested daylily crowns, can’t
our government protect us? If only it were that simple. APHIS, the agency
of the U.S. Department of Agriculture in charge of inspecting incoming
plant material, faces an avalanche of imports. To make matters worse,
daylilies enter the U.S. with their leaves stripped off, so a few rust
spores clinging to the crowns are all but undetectable. Stopping daylily
rust by inspecting incoming daylilies is mission impossible.
Another twist in the tale of daylily rust is that it can infect other
host plants besides daylily. A perennial called Patrinia, six species
of which are grown in the U.S., has a special place in the story because
it’s an "alternate host" for the daylily rust fungus. When
the rust infects Patrinia, it can complete its life cycle and make
new genetic types of the rust -- a very bad thing, unless you are the
rust. On the hopeful side, no rust infections of Patrinia have
been observed so far.
In case you weren’t already nervous, another suspected alternate
host is -- get ready for it -- hosta. Hosta and daylily are the co-champions
of the herbaceous perennial world in popularity. But so far, hosta hasn’t
become infected with daylily rust either.
If you find daylily rust in your landscape, don’t abandon hope.
First, remove all the infected foliage and burn or bury it. Sterilize
your shears with 70 percent alcohol, 10 percent bleach, or Lysol afterward
to prevent the spores from spreading. If you did the removal by hand,
wash your hands or gloves thoroughly. Save a few leaves, however, and
either bring them to your County Extension Office or mail them directly
to the Plant Disease Clinic, 351 Bessey Hall, Iowa State University, Ames
50011. We’d like to track the extent of the daylily rust problem
in the state, and your samples will help us do it.
New foliage can be protected as it emerges by spraying with systemic
fungicides such as propiconazole (Banner MAXX), azoxystrobin (Heritage),
flutolanil (Contrast), or myclobutanil (Systhane, Eagle). Be sure that
the product you use is labeled for either daylilies or ornamentals in
general.
Since daylily rust is a new disease, many facets of its life are still
shrouded in mystery. For example, nobody knows yet whether the fungus
survives Iowa winters. In a hopeful scenario, the fungus could be wiped
out by sub-arctic blasts. But don’t bet money on it. More than likely,
daylily rust will just be added to the list of obnoxious pests that have
invited themselves into our landscapes.
If you find daylily rust but don’t want to send in a sample for
confirmation, I’d still like to know about it. I can be contacted
by phone, (515) 294-0579, or e-mail, mgleason@iastate.edu
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ml: isugarden
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