When daylily rust first appearedin the U.S. in 2000, little was knownabout its potential spread andimpact. Today, we know that it gen-erally is winter-killed in zones ascold as USDA zone 6. In zone 7,rust persists in some areas but notothers. In zone 8 and warmer, rustmay be present year-round.Anywhere green daylily leaf tissuesurvives, there is a chance rust can survivewith it.

Diseased leaves are unsightly and oftendie prematurely. Badly diseased plants maydwindle away, but most daylily cultivars arenot that badly affected. Although it blem-ishes the leaves and sometimes the scapes,it does not infect the flowers, consequent-

ly, many gardeners find rust toler-able at low levels. In some statesrust is a more pressing issuebecause growers cannot selldaylilies if rust is found anywherein the nursery.

Rust severity varies accordingto weather conditions. Rainy peri-ods and mild temperatures in the60 to 80 degree Fahrenheit rangefavor rust, while low temperatures,high heat, or drought hold it at

bay. In many areas rust seems to break outmost strongly in fall.

Rust control has a single goal:Preventing rust infections by reducing thenumber of spores being released into thegarden. Rust infections damage leaveswhile growing inside them, then producepustules filled with spores that are the

cause of new infections. The fewer sporesproduced, the fewer new infections thatwill occur, and therefore less damage to theleaves.

The most important weapons you haveare “cultural” controls as outlined in thefirst steps below. Fungicides are not the firstline of defense, they are the heavy artilleryto use when all else fails. If you have achoice, don’t use them. Many are rated as“bad actors” by the Pesticide ActionNetwork (PAN), having potentially haz-ardous side-effects on you or the environ-ment.

1. Eliminate the most rust-prone culti-vars from your garden. Daylily cultivarsdo vary in how susceptible they are to rustinfection, how badly they are damaged byit, and how many spores are produced ifthey become infected. In one study, the

Controlling Daylily

By Patricia Crooks Henley, Ph.D.Region 2, Ohio

Rust

Patricia CrooksHenley

DJ Fall 08Scientific Forum

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most susceptible cultivar produced over36,000 spores per square centimeter of leaf,whereas the most resistant cultivars pro-duced none in the same time period! (Li, etal., 2007). Considering that the rust dis-ease can cycle from a single infecting sporeto a new pustule producing thousandsmore spores in as little as 10 days, thismakes a huge difference in the amount ofdisease that is likely to develop over theseason. If you want to keep some of therust-prone ones, try grouping them togeth-er in an “intensive care” bed.

See the sidebar for the address ofRebecca Board’s Rust Survey website thatlists rust susceptibility ratings of numerouscultivars, and please contribute your ownobservations!

2. Watch for rust pustules developing.Remove diseased foliage as soon as youcan. The pustules are the small, roundedblemishes which are filled with looseorange spores. If you’re in doubt, try wipingthe leaves on both sides with a white tis-sue; a powdery orange deposit indicatesrust. Diseased foliage should be collectedin plastic bags or heavy-paper yard-wastebags. Try to handle the foliage in a way thatminimizes shaking spores loose into the air.If practical, completely removing all thefoliage once a year can reduce spore levelssubstantially. In transition climate zones,growing deciduous daylilies can reducecarryover.

3. Promote leaf dryness by spacingplants well and avoiding sprinkler irriga-

tion. To germinate and infect the plant,rust spores need moisture for about 4hours. Longer moist periods permit greaternumbers of spores to germinate. Moisturetrapped inside clumps creates an idealenvironment for disease. Leaves will dryfaster if daylily clumps are spaced well-apart, and the clumps are divided as need-ed to prevent crowding. It’s also easier to“scout” for rust and to remove diseasedleaves when plants are not crowded. Dripirrigation is recommended rather thansprinklers.

Many non-commercial daylily growersreport that cultural practices like the onesabove control rust well enough they don’tfind it necessary to use fungicides. Rustmay still be present, but at levels they findtolerable. Daylily sellers, though, do notalways have the option of tolerating rust intheir gardens. Some state departments ofagriculture require nurseries to be rust-freeto be certified. In other states, rust can bepresent in the nursery, but any plantswhich are actually sold are supposed to berust-free.

4. Keep track of the disease cycle inyour garden. Keep a log of the dates whenrust appears in your garden. Record rainevents and temperature cycles in your gar-den and try to relate them to rust outbreakor quiescent periods. Try to figure outwhether there is a pattern of rust occur-rence; it tends to be seasonal in mostregions. If you decide to use sprays as partof your rust control program, knowing

when the most severe rust episodes arelikely to hit will help you target the treat-ments for best results.

5. If necessary, use fungicides.Fungicides cannot make sick leaveshealthy again. The lesions and damagewon’t go away. The purpose of fungicides isto protect the leaves from becoming dis-eased, or from getting worse. To do that,fungicides have to be applied as soon asrust appears, before a lot spores are pro-duced. By spraying early in the diseasecycle, you can use a lower rate of fungicideand space the sprays further apart, savingmoney and time. Remove as much of thediseased foliage as possible before applyingfungicides.

Before you buy a fungicide, read theinformation on the label. Does it say it canbe used on daylilies (or at least “ornamen-tals”)? Does it say it will control Pucciniarust diseases? That’s the group daylily rustbelongs to. What protective equipment doyou need to wear while you are mixing it,and while you are applying it? How oftenshould you apply it? What pH should thewater be? Is there a maximum number oftimes it can be applied per season? Thelabel tells you all this and much more thatyou need to know. You can find samplelabels and Material Safety Data Sheetsonline at the PAN and other sites. For yoursafety, fungicides and all other pesticidesshould only be purchased and stored intheir original containers.

Rust is seen outdoors and in a container grown daylily.

Sue Bergeron photos

See Rust, page 42

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Fungicide names are confusing! A fungi-cide product might be described by severaldifferent terms, such as its chemical class,its mode of action, its active ingredient,and one or more brand names. No wonderwe can’t keep them straight. Recognizingthis problem, manufacturers have startedlabeling fungicides with a “Group” designa-tion, according to the active ingredient’smode of action. These groupings clarifyhow to use fungicides in ways that mini-mize the risk of fungi becoming resistant.When fungi develop resistance to a fungi-cide, they are no longer controlled by it;you don’t want that happening in your gar-den! The main approach to minimizingresistance is to rotate applications of fungi-cides from different Groups so that fungiare not exposed to the same kind indefi-nitely.

The fungicides which have most consis-tently been shown effective against daylilyrust and are labeled for that use in the U.S.fall into three mode of action Groups1:

Group 3 systemic fungicides (DMIinhibitors). Two which have performedwell in most studies are triadimefon(Bayleton, Strike, and other brands) and

propiconazole (Banner Maxx and otherbrands).

Group 11 systemic fungicides(Stobilurins). Three are currently labeled:azoxystrobin (Heritage), pyraclostrobin(Insignia), and trifloxystrobin (Compass).

Group M contact fungicides, particu-larly chlorothalonil (M5) and mancozeb(M3). These two are available in severalbrand names and various concentrations.

There are other products which may beeffective against daylily rust, but the oneslisted are the basis of most of the successfulrust control programs used by experiencedgrowers. The basic strategies of rust controlnever change, but the products availabledo, so watch for new information. Be waryof claims that one product is the same asanother. Two products can have the sameactive ingredient and even the same con-centration but have different formulations,which greatly affects how they are used.

How do you decide which ones to use?There is not a lot of difference in how wellthese fungicides have controlled rust onplants in greenhouses in research studies.But there are differences in how well theywill control rust outdoors in gardens, inhow they should be used, in safety issues,and in cost. One important factor is thefrequency that you find it necessary to treatin order to control rust in your garden. If

it’s only once or twice a year, rotation is nota critical issue. You could choose just oneproduct. If you need to treat frequently andyou plan to use any of the systemics(Groups 3 and 11 here), you need to use atleast two products and they must be fromtwo different Groups (3, 11, or M).

The Group M contact fungicides are theleast costly, out-of-pocket. They can onlyprotect the leaf surfaces they actually cover(contact). That makes it necessary to spraythe undersides of daylily leaves if you aretrying to protect them with a contact fun-gicide alone, because rust can easily infectdaylily leaves from the undersides.Researchers have obtained excellent rustcontrol with these contact fungicides

Rustcontinued from page 41

1Outside the U.S., fungicide Groups maybe designated by letters instead of num-bers, otherwise they are the same. Brandnames may also be different. The commonname of the active ingredient, such aschlorothalonil, does not change. Not everyfungicide is available in every country, noreven in every state in the U.S.. Sometimesthe same product is sold under more thanone brand name, but it can be difficult todetermine whether they are actually thesame. Always use the product that is cor-rectly labeled for the situation in whichyou are applying it.

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alone, but they were treating pottedplants with one or a few fans each.Daylily clumps in gardens are muchharder to spray thoroughly!

The risk that fungi will becomeresistant to contact fungicides is verylow, so they do not have to be rotated.Chlorothalonil is the most widelyavailable and can be mixed with manyother fungicides (check the labelsfirst). Example brands are Bravo,Daconil, and Fung-onil. Mancozeb is alittle harder to find; Protect DF andBonide Mancozeb Flowable are twoexamples.

Systemics have several advantagescompared to contacts. They areabsorbed into the leaf, where they pro-tect it from infection by spores thatland on the undersides. Contacts can’tdo this. Systemics may be activeagainst infections that already starteda few days before the fungicide wasapplied. Systemics are generally effec-tive over a longer period than con-tacts. Systemics do have one impor-tant disadvantage, which is that fungiare more likely to become resistant tothem; that is why rotation is needed ifthey are used frequently.

The strobilurins in Group 11 are the

most effective systemics against daylilyrust, and also the most expensive. Dr.James Buck reported: “In some of ourwork (unpublished) we observed thatthe strobilurins were the only class offungicide that significantly loweredspore production from active lesions”[personal communication, 2008]. Ofthe three listed, Compass is the mosteconomic for a small garden. It’s avail-able in a 2-ounce size for about $70 (or8-ounce for $230). Heritage is avail-able in a 4-ounce for about $170 (or 16ounce $500). Currently, Insignia(which was tested as BAS500) onlyseems to be available in a 2.4-poundsize for about $370. Very smallamounts of these products are used,about 1/8-1/2 teaspoon per gallon(again, check the labels), so a littlegoes a long way.

Where rust is a threat year-round,and treatments are ongoing, usingmore than one product and rotatingthem properly becomes paramount.Read the label of the product you areusing, but in most cases you should

never make more than three consecu-tive applications of any one systemicfungicide nor of any products from the

Certain Patrinia species are the only other plants known to besusceptible to daylily rust and in Asia allow the disease to re-develop after winter even where the daylilies are deciduous.

See Rust, page 44

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same Group of systemics. Remember that to rotate systemics, youneed at least one product each from two different Groups. Thatmeans, for example, that alternating Bayleton and Banner Maxxwould not be properly rotating because both are Group 3. Anyproduct from Group 3 rotated with any product from Group 11 orGroup M would be acceptable. Group M fungicides can be used inseveral ways depending on what is allowed by the labels: 1) alone;2) combined with any systemic or any other contact; 3) in rota-tion with any systemic; 4) both in combination and rotation.

Many plant pathologists recommend adding a contact fungicideto each application of a systemic to assist in killing spores.Although alternating two different contact fungicides seems to becommon practice among daylily nurseries, you could add the sameone each time if it can be mixed with the other products you areusing.

An example of an intensive rotation program using the aboveproducts:

First application: Group 3 DMI (such as Bayleton or Banner Maxx) + mancozeb

Wait 14-28 days (if less than 14 days, repeat this combina-tion once – see below)

Second application: Group 11 strobilurin (Compass, Heritage, or Insignia) + chlorothalonil

Wait 14-28 days (if less than 14 days, repeat this combina-tion once – see below)

Repeat the cycleThe “waits” given reflect the long residual activity of these sys-

temic fungicides. The labels might permit using them as often asevery seven days, but if you find it necessary to use any of thesesystemics at intervals of less than 14 days, use the same one twicebefore switching. The reason being the residual activity of thesesystemics can extend beyond two weeks. By repeating the samefungicide at close intervals the two applications reinforce eachother, building and maintaining an effective level of that fungicidefor a longer period. Then, while you make the next two applica-tions using different fungicides, the longer reprieve allows the firstcombination to dissipate from the plant before it is applied again.This meets the goal of rotation. When rust threat is highest andwhen daylilies are actively growing, use the highest rate (amount)of the fungicide per application that the product’s manufacturerrecommends.

Systemic product labels may have limits stated for the numberof times they can be used, or the total amounts per year. For exam-ple, Heritage currently states that it should not be used more than8 times per year. To avoid overusing these systemics, you may needto do some applications using only the contact fungicides. If so,save the systemics for periods when rust threat is highest based onyour experience with the disease cycle.

The systemic products listed have given good control of daylilyrust for at least a two-week period in research studies (e.g. Muelleret al., 2004, and others). Most daylily growers report that theyspray every two weeks when conditions are optimal for rust devel-opment. When conditions are less favorable such as during coolwinters and hot summers in the subtropics, every month seems tobe adequate. In the upper south, some growers report that just oneor two treatments in the early fall are enough to give satisfactorycontrol.

The three most important words in spraying fungicides?Coverage, coverage, coverage. Spray until all the leaves are thor-oughly wet, all the way inside the clump. Try to cover the under-sides of the leaves also. Remember that the young leaves in the

center of each daylily fan are actually growing from the bottom up,so the newest portion of each leaf is at the bottom. New growthhas to be treated in order to be protected.

Keep a log of your spray applications and make notes on howsuccessful they were. Realize that it may be 10 or more days beforepre-infected leaves show pustules. So, you may see some rust eventhough your sprays were successful in controlling spores that land-ed after the treatment.

Reading the labels of the fungicides you’ve chosen, you may findthey can also control various other diseases which cause problemsfor daylilies. Names like Aureobasidium, Colletotrichum, Fusarium,Pythium, Phytophthora, Rhizoctonia, Sclerotium may be included. Atfirst this may sound terrific. Think of it, controlling so many dis-eases with a single product. On the other hand, think of this – ifyou misuse or abuse that product, resistant pathogens of all thosediseases could develop in your garden! Also, the fungicide may beaffecting beneficial fungi in the soil, directly and indirectly. Manyreasons exist to use fungicides thoughtfully and conservatively.

The author welcomes feedback on this article, additional infor-mation, or questions relating to it, which may be published later.Please write: daylily@greenapple.com.

ReferencesBuck, James W. 2008. Personal communication via email from

the University of Georgia, University Experiment Station, Griffin,Georgia.

Li, Y. H., Windham, T., and Trigiano, R. N. 2007. Microscopicand macroscopic studies of the development of Puccinia hemerocal-lidis in resistant and susceptible daylily cultivars. Plant Disease91(6):664-668.

Mueller, D.S., Jeffers, S.N. and Buck, J. W. 2004. Effect of tim-ing of fungicide applications on development of rusts on daylily,geranium, and sunflower. Plant Disease 88(6):657-661.

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The single best source of information about daylily rust isSusan Bergeron’s Daylily Rust Information Page. The site hasimages, and lots of links, both general and specific.

http://web.ncf.ca/ah748/rust.html

Find (and contribute) rust resistance ratings for daylilycultivars on Rebecca Board’s Rust Survey website.Participating requires filling out a garden form, which can be ascomplete or as brief as you choose.

http://www.daylilyrust.org/survey.html

The Pesticide Action Network (PAN) Pesticide Databasecan be searched by name of product, active ingredient, or man-ufacturer. Has links to product specimen labels and safety datasheets (MSDS). Gives toxicity to humans & animals, and envi-ronmental hazards. Rates some as “bad actors”. Lists productswhich are simply re-packaged versions of others, allowing youto tell which ones are actually identical.

http://www.pesticideinfo.org/

Online sources of informationon Daylily Rust

DJ Fall 08