Producing Larkspur as Cut Flowers · ed, the larkspur plants will grow rapidly in cool fall...

Stanton Gillregional Extension specialist

Central Maryland Research and Education Center

Ethel Dutkyplant pathologist

Department of EntomologyUniversity of Maryland at College Park

Russell Balgeregional Extension specialist

Western Maryland Research and Education Center

Tom Blessingtonregional Extension specialist

Central Maryland Research and Education Center

David RossExtension agricultural engineer

Department of Biological Resources EngineeringUniversity of Maryland at College Park

Bryan Butlerfaculty Extension assistant

Carroll County

Ginny Rosenkranzfaculty Extension assistant

Wicomico and Worchester Counties

Suzanne Klickcommercial horticulture technician

Central Maryland Research and Education Center

IntroductionLarkspur, Consolida spp., are excellent

cut flowers—both for fresh and dried oreverlasting markets. Many cut flowers arepopular for short periods of time, oftenattracting public attention for less than 5years, then fading from demand. Themarket for good quality larkspur has beenstrong for many years, past the period of“fad flowers,” and it continues to stayrobust. The alluring flower shape, widerange of colors, and appealing foliage allcombine to make larkspur a popular, mar-ketable cut flower. The flowers tend to besomewhat fragile and relatively short-lived in the vase (under 7 days), makingproduction for local markets very appeal-ing.

Larkspur grow to their full potential inclimates with cool, moist summers.Growers must adopt practices that takeadvantage of the cooler seasons to suc-cessfully grow larkspur as a cut flowercrop in Maryland. Maryland growersoften establish sequence plantings oflarkspur during the cool weather ofSeptember through heavy frost. Plants

Producing Larkspur as Cut Flowers

Fact Sheet 713

P97

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ReferencesArmitage, Allan M. 1993. “Specialty

Cut Flowers.” Athens, GA: Varsity Press,Inc.

Gill, Stanton A. and J. Sanderson. 1997.“Ball Greenhouse Pest Identification andIPM Control.” (In press.)

Nau, Jim. 1995. “Ball PerennialManual: Propagation and Production.”Batavia, Illinois: Ball Publishing.

Powell, Charles and Richard Linguist.1992. “Ball Pest and Disease Manual:Disease, Insect, and Mite Control onFlower and Foliage Crops.” Batavia,Illinois: Ball Publishing.

Woods, Christopher. 1992.“Encyclopedia of Perennials.” New YorkCity: Facts on File, Inc.

Reviewed byDr. John Dole, Oklahoma State

UniversityDr. Will Healy, George Ball Seed

Company, Inc.

Illustrations byRaymond Bosmans, Regional Specialist,CES Home and Garden Information

Center

Note: When trade names are included, no dis-crimination against similar products is intended.Mention of trademarks in this publication doesnot constitute an endorsement by the CooperativeExtension Service.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30,1914, in cooperation with the U.S. Department of Agriculture, University of Maryland at College Park,and local governments. Thomas A. Fretz, Director of Cooperative Extension Service, University of Maryland at College Park.

The University of Maryland is equal opportunity. The University’s policies, programs, and activities are in conformance with pertinent Federal and State laws and regulations onnondiscrimination regarding race, color, religion, age, national origin, sex, and disability. Inquiries regarding compliance with Title VI of the Civil Rights Act of 1964, as amended; TitleIX of the Educational Amendments; Section 504 of the Rehabilitation Act of 1973; and the Americans With Disabilities Act of 1990; or related legal requirements should be directed tothe Director of Personnel/Human Relations, Office of the Dean, College of Agriculture and Natural Resources, Symons Hall, College Park, MD 20742.

established in the fall grow rapidly incool, moist springs, with heavy flowerproduction in May and June and occa-sionally into July if the weather remainsfavorable.

The genus of larkspur was recentlychanged from Delphinium to Consolida.Two species of larkspur are used for cutflowers: Consolida ambigua and Consolidaorientalis. C. orientalis is more uprightthan C. ambigua, and colors are oftenshades of bright pink and purple. C.ambigua have more branches initially andcolors are usually light pink or blue. Mostof the outstanding larkspurs for cutflower production are C. orientalis vari-eties.

Culture

Field Production

PropagationLarkspur is commonly produced by

direct seeding into the field. Somegrowers start or purchaseseedlings grown in greenhouseplug trays, and transplant lark-spur plugs into the field orgreenhouse growing beds.

Larkspur has a reputationfor poor germination. Seedsthat germinate best arethose planted 4 to 6months after harvest.Seed 1 year or older oftenhas germination rates ofless than 50 percent.Stored seed should berefrigerated until need-ed, but held for under 1year. An ounce of seedyields approximately 5,000plants.

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Larkspur seed does not germinate wellwhen soil temperatures are held above 75 °F. Germination will be improved bychilling seed (35 to 40 °F) for at least 7 to14 days prior to planting. In Maryland,optimum seeding times for field produc-tion are from September through heavyfrost. Most growers will plant a series ofsequence plantings at 2-week intervals.Germination takes place 12 to 20 daysafter sowing. Once the seed has germinat-ed, the larkspur plants will grow rapidlyin cool fall weather. Larkspur plants plant-ed in fall flower 4 to 6 months after plant-ing.

An alterna-tive is to start

seeds in a green-house during the

winter and trans-plant the plugs in

early spring. Forgreenhouse growing, use

a germination temperature of70 °F, with a light covering of coarse

vermiculite. Transplants from the green-house should be conditioned at tempera-

Summary• Select larkspur cultivars and site.• For field production, prepare

seed beds in the fall and plant aseries of sequence plantings at 2-week intervals.

• Grow plants in full sun, prefer-ably in raised bedswith trickle irriga-tion.

• Monitor for aphidsand cyclamenmites.

• Monitor for dis-eased plants andpromptly removethose that areinfected.

Consumer Care

• Recut stems under water and placeflowers in clean warm water contain-ing a floral preservative.

• Avoid temperature extremes such asfreezing or temperatures over 95 °F.

• Keep flowers away from rapid airmovement.

• Avoid keeping flowers near ripeningfruit, which emits ethylene.

• Pretreatment. Pulse with silver thio-sulfate (STS) to minimize ethylenedamage and prolong vase life. Use acommercial silver solution accordingto label directions, preferably for a 1-to 2-hour treatment. The STS solu-tion must be processed for silverrecovery before it can be disposed ofdown a drain. Commercial devices,such as a Superbatcher, are speciallydesigned to remove the silver fromSTS. STS is not very stable, giving thesolution a relatively short shelf life.Unfortunately, it is not always easyto determine whether your STS solu-tion is still active. Test kits are avail-able to test the solution’s effective-ness.

• Hydration. Hydrate in clean, warmwater (80 to 90 °F) at pH 3.5 to 4.0.

• Preservation. Use a floral preserva-tive for maximum longevity.

• Temperature. Refrigerate at 35 to 40 °F.

devices that monitor soil moisture andcan be used to help the grower decidewhen to irrigate. (For more information,refer to University of Maryland ExtensionService Bulletin 312, ”Soil MoistureSensors for Irrigation Management.”)

NutritionAdding a 1- to 2-inch layer of compost-

ed organic material and tilling it in willgreatly benefit larkspur growth. Larkspurplants also respond favorably to applica-tions of nitrogen fertilizer. If using trickleirrigation, fertilize on a weekly basis with100 parts per million (ppm) of completefertilizer based on nitrogen. Water-drivenfertilizer injectors are available that addthe correct proportion of concentratedsoluble into the irrigation water. If pro-ducing larkspur without trickle irrigation,side dress with a complete fertilizer (10-5-10 or 10-6-4 ratio) at 1 pound per 100square feet of production row.

Greenhouse ProductionLarkspur is best grown in groundbeds

to facilitate production and harvesting.The seeds should be sown fromSeptember through November. Maintaintemperatures at 50 to 55 °F for 8 to 10weeks. Raise temperatures to 55 to 60 °Fafter this time. Larkspur needs daylengths of 16 hours to flower. The daylength can be extended with lighting orwith 2-hour night break lighting usingincandescent lamps.

NutritionGreenhouse-grown larkspur needs

weekly applications of a dilute solublecomplete fertilizer (for example, 20-10-20or 15-5-15 ratio) at 100-200 ppm basedon nitrogen.

tures below 55 °F for 4 to 6 weeks beforebeing moved into the field in April.Yields of cut flowers seed-started in green-houses are generally not as heavy asyields from plants field-started in the fall.

Site selectionSelect a location that receives at least 8

hours of direct sunlight. A source ofwater near the site is good because an irri-gation system is frequently needed forbest quality production. Larkspur growsbest in well-drained soil with a pH of 6.0to 7.0. Using a raised bed improvesdrainage and will also warm the bed earli-er in the spring. Wide spacing of 10 to 12inches between plants will provide morecut flower stems per plant. The yield persquare foot will increase with a closerspacing of 4 to 5 inches between plants,but will decrease per individual plant.

SupportMost larkspur cultivars grow to a

height of 3 to 4 feet. Unsupported flowerswill often fall over with the stems turningupward. To maintain the quality of cutflowers, one or two layers of net or wiresupport (6- to 8-inch openings) are rec-ommended to help hold flowers upright.

IrrigationInstalling a trickle irrigation system is a

worthwhile investment. Irrigation is bestachieved using irrigation rowcrop tape orrowcrop emitter tubing that lies downthe row with emitters spaced 6 to 12inches apart. Two or three rowcrop tapeson a raised bed will water several rows ofplants across the bed. Coarse soils needmore tapes. Water frequently enough tomaintain a good soil moisture. Use ascreen filter of 100 to 140 mesh to pre-vent clogging and use a small pressureregulating device set at 8 to 10 psi toensure the proper operating pressure forthe trickle tubing. Tensiometers are

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Cultivars•Consolida orientalis:

Giant Imperial series—The standardof the industry. Plants grow 3 to 4feet tall. Colors: carmine, deep blue,deep rose, light blue, lilac, pink,salmon, and white.Messenger series—Plants are 3 to 4feet tall and flower 2 weeks earlierthan the Giant Imperial series.Colors: Blue, lilac, rose, and white.Early Bird series—Earlybird flowers2 to 3 weeks earlier than GiantImperial. Plants are 3 to 4 feet tall.Colors: blue, lilac, rose, white, andmixed.QIS series—Very uniform plants andthick stems. Plants grow 2 to 3 feettall. Colors: carmine, dark blue, lightpink, lilac, rose, white, and mixed.

Pests

Major DiseasesThe most important diseases of lark-

spur cut flower production are damp-ing off of seedlings (Pythium andRhizoctonia fungi), Botrytis, powderymildew, and Southern blight.

Damping off and seedling rootrots

Several species of the water moldPythium attack larkspur seedlings. Bothcool and warm temperature species arereported. Wet conditions favor Pythiumdiseases. Pythium may rot the germinat-ing seed (preemergence damping off), orcause root rot that stunts or killsseedlings (postemergence damping off).Pythium produces a tan, water-soakedappearance in roots and stem. The rootcortex may slough off leaving the whiteroot vascular cylinder exposed, like finewhite threads.

the flowers by hanging flower stemsupside down and drying at 70 to 80 °F for10 to 14 days. A well-ventilated dryingbarn is ideal for preserving larkspur.

Postproduction Factors

Retail handling• Recut stems. After bringing larkspur

in from the field, recut stems underwater to prevent a water uptakeblockage.

• Ethylene. Flowers are highly sensi-tive to ethylene, with resulting pre-mature dropping of flowers. Flowerswill react when exposed to ethyleneat 3 ppm for 24 hours at 70 °F.Causes include shipping with mixed-fruit or decaying plant material.

blooms have fully opened. If shipping theflowers, try to harvest before the lowerone-third of the flower stem has opened.For direct markets, you may choose toharvest when one-half to three-quartersof the flower stem has opened. The vaselife of larkspur is between 5 to 7 days.The flower blooms are highly sensitive toethylene and will shatter in its presence.To hold larkspur for 1 to 2 days, placestems in fresh water, keeping themupright and maintaining temperatures of34 to 40 °F.

Everlasting salesLarkspur are relatively easy to dry for

sale as everlasting flowers. For everlastingflowers, harvest when the majority of theflowers have opened, but before the bot-tom flower petals have dropped.The feathery foliage does notneed to be removed when dry-ing the flower stems. Air dry

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Chemical control of cyclamen mites.Since cyclamen mites are found in cryp-tic (small, hidden) locations on the plant,spray applications must be made as a finemist. Use of a spreader sticker to increasechance of contact with the pest is recom-mended. Check with your localCooperative Extension office for current-ly labeled miticides. Usually, the bestaction is to destroy infested plants beforethe problem spreads in the planting.

Weed ControlTo maximize both floral quality and

quantity, weed control is essential inboth field and inground greenhouse pro-duction of larkspur. Competition fornutrients, moisture, and light can bereduced with a good weed control pro-gram. In a greenhouse, soils can be steamsterilized at 160 °F for 30 minutes to killmost weed seeds. A weed barrier of 2- to4-mL black plastic with holes made forplacement of plant plugs or seeds cangreatly reduce the need for weeding.Unfortunately, the black plastic tends tocause the soil temperatures to rise, whichwill affect the quality of the larkspurcrop. A light layer of leaves or bark canbe laid over the black plastic to reducethe heat buildup.

Another option for weed control is touse organic mulch as a surface applica-tion. If seeding is done in the fall, a 1-inch organic mulch layer (compostedleaves or grass clippings) can be appliedclose to the plants after they germinate.The mulch layer will reduce germinationof fall-germinating weeds. In the spring,if the organic mulch layer has thinnedout, an additional 1-inch layer can beplaced on the soil to reduce germinationof spring-germinating weeds.

A chemical option to prevent annualweeds from germinating would be toapply a preemergent herbicide. The pre-

emergents must be applied after the lark-spur seed germinates to prevent inhibit oflarkspur germination. If plants are estab-lished in the fall, preemergent herbicidescan be applied to weed-free soil aroundgrowing plants in the spring to controlspring-germinating annual weeds. Thepreemergent Dacthal prevents germina-tion of several annual weed grasses and afew broadleaf annual weeds. The preemer-gent Pennant is effective against annualgrasses, yellow nutsedge, and severalbroadleaf annual weeds. Check with yourlocal Cooperative Extension Service forcurrent recommendations on other pre-emergent herbicides labeled for use infield-produced cut flowers.

Glyphosphate (sold under severalbrand names, including Round-up) canprovide postemergent control of grassesand broadleaf weeds. Apply a 33 percentGlyphosphate solution with a wick appli-cator. Use extreme caution with this solu-tion. Be careful not to make contact withthe larkspur or the Glyphosphate will killyour desired plants as well as the weeds.

Some growers have used methyl bro-mide to fumigate the soil before directseeding of larkspur. Used for years, thissoil fumigant kills weeds, seeds, andmany insect and disease species. It ispresently still available for use by certifiedpesticide applicators, but is being phasedout of the market because it is extremelytoxic. Basamid (granular formulation) canalso be used as a soil fumigant and ismuch safer than methyl bromide.

Harvesting LarkspurFresh market sales

Larkspur flowers start opening from thebottom and progressively open up fromthe flower stem to the top. For fresh mar-ket sales, harvest when several lower

The fungus Rhizoctonia solani can alsocause damping off and seedling blight.Usually Rhizoctonia is favored by warmconditions. When compared to Pythium,Rhizoctonia lesions are more defined, withtan, sunken areas. Sometimes the lighttan, fine “cob web” mycelium ofRhizoctonia can be seen on blighted plantparts and growing across the soil surface.

To differentiate Pythium fromRhizoctonia, use an Alert on-site diagnos-tic kit. This will permit you to select thecorrect fungicide for control.

Basic good horticultural practices, sani-tation, and providing optimum condi-tions for seed germination and seedlinggrowth can prevent most damping-offlosses. Selecting a well draining mediaand watering early in the day so soildrains well before nightfall helps controlPythium. SoilGard, a biological fungicide,can be added to media to provide excel-lent control of both Pythium andRhizoctonia.

Botrytis blightsBotrytis can attack seedlings, but it is

especially damaging when it spots andblights flowers. High humidity and a filmof water on plant surfaces is necessary forBotrytis to infect plant tissues. Thus, anycultural practice that reduces periods ofleaf wetness (trickle irrigation, plant spac-ing to improve air circulation, use of hor-izontal air flow fans in greenhouses, etc.)will reduce the risk of Botrytis.

Botrytis produces a small, defined spotthat may rapidly enlarge to blight theflower, leaf, or stem. Weak plant tissuessuch as yellowing senescent foliage,flower petals, and wounds are easilyinvaded by Botrytis. Under humid condi-tions a gray mold is produced on blightedtissues. This gray mold is diagnostic ofBotrytis. Look for this aerial gray moldearly in the morning or incubate dam-

aged tissues in a moist chamber overnightto promote the formation of spores.

The Botrytis fungus has developedresistance to several major classes ofchemical fungicides, including the benz-imidazoles (e.g., Cleary’s 3336 andDomain) and the dicarboximides (Chipco26019), making chemical control diffi-cult. When extended periods of wet over-cast weather occur, it may be helpful tospray with mancozeb or use ExothermTermil smoke in the greenhouse. The cop-per fungicide Phyton 27 is also registeredfor Botrytis control on flowers.

Powdery mildewSome larkspur cultivars are susceptible

to powdery mildew caused by the fungusErysiphe polygoni. Symptoms includetwisted and distorted foliage and whitespots and patches on foliage, stems, andbuds. Flower buds may fail to open andflowers may be distorted and unsalable.Weather conditions that favor powderymildew are sunny, warm, dry days, andcool nights.

Several systemic fungicides (e.g.,Funginex, Terraguard, Strike, Banner) andsummer oil sprays all provide good con-trol of powdery mildew. Some larkspurcultivars are less susceptible. Keep goodrecords of disease incidence on each culti-var you grow; you can then select resis-tant cultivars.

Southern blightThe Southern blight fungus Sclerotium

rolfsii (also called Sclerotium delphini bysome authors) can be a serious problem infield-grown larkspur during hot weather.The fungus remains in the upper inchesof field soil and is only active during peri-ods of hot weather when soil tempera-tures rise into the upper 70s. The fungusattacks the plant at the soil surface, caus-ing a rapid wilt and crown rot of individ-

76

ual scattered plants in the field. Closeinspection of wilting plants will findwhite wefts of mycelium on the stem,often webbing soil particles and mulchto the stem. The small (about 1/8 to1/4 inch), spherical, white to brownsclerotia are formed on stems and soil.Presence of the sclerotia is diagnostic ofSouthern blight.

Several management practices willreduce Southern blight. Deep tillage buriesthe sclerotia and will reduce the diseasebecause the sclerotia require warmth andoxygen to grow. Incorporating organicmatter will help by promoting decay ofthe sclerotia during the fall, winter, andspring. Wilting plants should be promptlyremoved along with any mycelium andsclerotia to reduce further increase in fun-gal inoculum in the field. Fungicide con-trols and biological agents that decay thesclerotia are in development and maysoon be widely registered.

Miscellaneous leaf spotsA number of fungi (Cercospora ,

Ramularia , Ascochyta , Phyllost icta ,Septoria) are reported to cause leaf spotson larkspur. Lab examination is neededto differentiate these minor leaf spotdiseases. All are promoted by extendedperiods of leaf wetness. Fungicidesprays can prevent infections andreduce spread if applied promptlywhen first leaf spots are seen. However,leaf spots are seldom serious enough tojustify a preventive spray schedule. Ifyou experience unusually prolongedperiods of wet weather, the fungicidesCleary’s 3336, Daconil 2787, ProtectTO, and others would be effective inpreventing most leaf spots.

Major Insects

AphidsAphids can rapidly become a major

pest in larkspur plantings if the popula-tion is left unchecked. Large populationsof aphids will result in noticeable honey-dew accumulations on foliage and flow-ers. Sooty mold fungus will grow on thehoneydew. Since aphids feed on plantphloem, they compete with the plant fornutrients. Heavy populations may mea-surably reduce plant growth and vigor.

Before you attempt to control aphidsyou need to identify the species of aphid.Samples can be submitted to your localCooperative Extension office for identifi-cation. Next, familiarize yourself with thebiology of the aphid in a particular crop.Note how fast they reproduce; whetherthey have a preference for feeding ononly certain parts of the plant, or a prefer-ence for feeding on certain species or cul-tivars of plants. One species of aphid thatis commonly found on larkspur is thegreen peach aphid, Myzus persica. Thisaphid species is very difficult to controlwith chemical applications.

Biological control of aphids. Aphidpopulations can be controlled by naturallyoccurring parasites and predators. If popu-lations of aphids are detected at the earlystage of development, you have theoption of using beneficial insects to con-trol aphid populations. Aphidoletesaphidimyza, a midge insect in the orderDiptera, can be used for controlling aphidsthat are difficult to control with chemicalssuch as the green peach aphid. This midgelives an average of 10 days and lays eggsclose to aphid colonies. The resultingorange midge larvae can kill aphids by bit-ing them at the knee joint and injecting aparalyzing toxin. They grow to maturityover a 3- to 5-day period. They will killfrom 40 to 60 aphids each, depending onthe aphid density. The midge will repro-

duce in the field. For pupation the larvaedrops to the ground and burrows aboutan inch into the soil before spinning acocoon. When you order the midge, it isgenerally shipped as a red-orange pupae.Place the pupal casing on the soil ofplants that have aphid populations. Ifaphid populations are extremely high,apply either 2 percent horticultural oil or2 percent insecticidal soap 1 or 2 daysbefore you release the midges. The releaserate for low aphid populations is 1 midgeper 10 square feet. For higher infestationsof aphids release them at 1 midge per 5square feet of growing area.

Chemical control of aphids.Horticultural oils, insecticidal soaps, andneem are three biorational chemicals thatsuppress aphid populations. Biorationalchemicals are materials that have shortresiduals and minimal impact on benefi-cial insects and nontarget organisms.Because these chemicals have no long-term residual effects, regular monitoring ofaphid populations is recommended andrepeated applications of the chemicalsmay be necessary.

Two systemic insecticides that givegood control of aphids are acephate(Orthene) and midicloprid (Merit). Oncea systemic has dried and been absorbedby the plant, the effect on beneficialarthropods is minimal.

Cyclamen mitesThe cyclamen mite, Phytonemus pallidus,

can cause injury to larkspur. The feedingdamage is exhibited in buds and flowersthat are distorted and often stunted. Leafbuds of badly infested plants are some-times completely destroyed. Adult andlarva of cyclamen mite occur in hiddenareas on the plant. They appear to avoiddirect light and require humidity levelsnear saturation, which is found betweentightly packed young leaves, or aroundflower buds.

Cyclamen mites are minute (less than0.2 mm). Often a grower will notice dam-age caused by these mites before actuallyseeing them. A pocket magnifier micro-scope with at least 30 X is needed to seethe mites. The outer cuticle is hard andshiny and there are relatively few setae(hairs) on the body compared to otherplant-damaging mites.

Female cyclamen mites lay eggs in clus-ters of two to three eggs, usually betweenyoung leaves of the bud or at the crownof the plant. Each female lays 10 to 40eggs over a 12- to 16-day life cycle. Eggsare white, ovoid, and smooth. The larva iswhite in color, and has six legs withmicroscopic claws and suction cups.Adult females are yellowish and haveeight legs. The males are often colorless toyellowish-brown. Males often pick up andtransport females transforming intoadults or adult females with their semi-erect hind legs. Female cyclamen mitescan reproduce without mating (partheno-genetically).

The cyclamen mite is very difficult tocontrol since its habitat is in tight, con-fined parts of the plant. Early detection ofdamage symptoms and subsequentdestruction of infested plants is the bestcourse of action cut flower growers cantake.

Biological control of cyclamen mites.Neoseilus (=Amblyseius) cucumeris(Oudemans) is a commercially availablemite that is used mainly to control firstand second instar thrips, but this phyto-seid mite also will feed on cyclamenmites. N. cucumeris has successfully beenused to control cyclamen mite on straw-berries, but additional field research needsto be conducted on use of this predaceousmite in cut flower fields.

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ual scattered plants in the field. Closeinspection of wilting plants will findwhite wefts of mycelium on the stem,often webbing soil particles and mulchto the stem. The small (about 1/8 to1/4 inch), spherical, white to brownsclerotia are formed on stems and soil.Presence of the sclerotia is diagnostic ofSouthern blight.

Several management practices willreduce Southern blight. Deep tillage buriesthe sclerotia and will reduce the diseasebecause the sclerotia require warmth andoxygen to grow. Incorporating organicmatter will help by promoting decay ofthe sclerotia during the fall, winter, andspring. Wilting plants should be promptlyremoved along with any mycelium andsclerotia to reduce further increase in fun-gal inoculum in the field. Fungicide con-trols and biological agents that decay thesclerotia are in development and maysoon be widely registered.

Miscellaneous leaf spotsA number of fungi (Cercospora ,

Ramularia , Ascochyta , Phyllost icta ,Septoria) are reported to cause leaf spotson larkspur. Lab examination is neededto differentiate these minor leaf spotdiseases. All are promoted by extendedperiods of leaf wetness. Fungicidesprays can prevent infections andreduce spread if applied promptlywhen first leaf spots are seen. However,leaf spots are seldom serious enough tojustify a preventive spray schedule. Ifyou experience unusually prolongedperiods of wet weather, the fungicidesCleary’s 3336, Daconil 2787, ProtectTO, and others would be effective inpreventing most leaf spots.

Major Insects

AphidsAphids can rapidly become a major

pest in larkspur plantings if the popula-tion is left unchecked. Large populationsof aphids will result in noticeable honey-dew accumulations on foliage and flow-ers. Sooty mold fungus will grow on thehoneydew. Since aphids feed on plantphloem, they compete with the plant fornutrients. Heavy populations may mea-surably reduce plant growth and vigor.

Before you attempt to control aphidsyou need to identify the species of aphid.Samples can be submitted to your localCooperative Extension office for identifi-cation. Next, familiarize yourself with thebiology of the aphid in a particular crop.Note how fast they reproduce; whetherthey have a preference for feeding ononly certain parts of the plant, or a prefer-ence for feeding on certain species or cul-tivars of plants. One species of aphid thatis commonly found on larkspur is thegreen peach aphid, Myzus persica. Thisaphid species is very difficult to controlwith chemical applications.

Biological control of aphids. Aphidpopulations can be controlled by naturallyoccurring parasites and predators. If popu-lations of aphids are detected at the earlystage of development, you have theoption of using beneficial insects to con-trol aphid populations. Aphidoletesaphidimyza, a midge insect in the orderDiptera, can be used for controlling aphidsthat are difficult to control with chemicalssuch as the green peach aphid. This midgelives an average of 10 days and lays eggsclose to aphid colonies. The resultingorange midge larvae can kill aphids by bit-ing them at the knee joint and injecting aparalyzing toxin. They grow to maturityover a 3- to 5-day period. They will killfrom 40 to 60 aphids each, depending onthe aphid density. The midge will repro-

duce in the field. For pupation the larvaedrops to the ground and burrows aboutan inch into the soil before spinning acocoon. When you order the midge, it isgenerally shipped as a red-orange pupae.Place the pupal casing on the soil ofplants that have aphid populations. Ifaphid populations are extremely high,apply either 2 percent horticultural oil or2 percent insecticidal soap 1 or 2 daysbefore you release the midges. The releaserate for low aphid populations is 1 midgeper 10 square feet. For higher infestationsof aphids release them at 1 midge per 5square feet of growing area.

Chemical control of aphids.Horticultural oils, insecticidal soaps, andneem are three biorational chemicals thatsuppress aphid populations. Biorationalchemicals are materials that have shortresiduals and minimal impact on benefi-cial insects and nontarget organisms.Because these chemicals have no long-term residual effects, regular monitoring ofaphid populations is recommended andrepeated applications of the chemicalsmay be necessary.

Two systemic insecticides that givegood control of aphids are acephate(Orthene) and midicloprid (Merit). Oncea systemic has dried and been absorbedby the plant, the effect on beneficialarthropods is minimal.

Cyclamen mitesThe cyclamen mite, Phytonemus pallidus,

can cause injury to larkspur. The feedingdamage is exhibited in buds and flowersthat are distorted and often stunted. Leafbuds of badly infested plants are some-times completely destroyed. Adult andlarva of cyclamen mite occur in hiddenareas on the plant. They appear to avoiddirect light and require humidity levelsnear saturation, which is found betweentightly packed young leaves, or aroundflower buds.

Cyclamen mites are minute (less than0.2 mm). Often a grower will notice dam-age caused by these mites before actuallyseeing them. A pocket magnifier micro-scope with at least 30 X is needed to seethe mites. The outer cuticle is hard andshiny and there are relatively few setae(hairs) on the body compared to otherplant-damaging mites.

Female cyclamen mites lay eggs in clus-ters of two to three eggs, usually betweenyoung leaves of the bud or at the crownof the plant. Each female lays 10 to 40eggs over a 12- to 16-day life cycle. Eggsare white, ovoid, and smooth. The larva iswhite in color, and has six legs withmicroscopic claws and suction cups.Adult females are yellowish and haveeight legs. The males are often colorless toyellowish-brown. Males often pick up andtransport females transforming intoadults or adult females with their semi-erect hind legs. Female cyclamen mitescan reproduce without mating (partheno-genetically).

The cyclamen mite is very difficult tocontrol since its habitat is in tight, con-fined parts of the plant. Early detection ofdamage symptoms and subsequentdestruction of infested plants is the bestcourse of action cut flower growers cantake.

Biological control of cyclamen mites.Neoseilus (=Amblyseius) cucumeris(Oudemans) is a commercially availablemite that is used mainly to control firstand second instar thrips, but this phyto-seid mite also will feed on cyclamenmites. N. cucumeris has successfully beenused to control cyclamen mite on straw-berries, but additional field research needsto be conducted on use of this predaceousmite in cut flower fields.

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Chemical control of cyclamen mites.Since cyclamen mites are found in cryp-tic (small, hidden) locations on the plant,spray applications must be made as a finemist. Use of a spreader sticker to increasechance of contact with the pest is recom-mended. Check with your localCooperative Extension office for current-ly labeled miticides. Usually, the bestaction is to destroy infested plants beforethe problem spreads in the planting.

Weed ControlTo maximize both floral quality and

quantity, weed control is essential inboth field and inground greenhouse pro-duction of larkspur. Competition fornutrients, moisture, and light can bereduced with a good weed control pro-gram. In a greenhouse, soils can be steamsterilized at 160 °F for 30 minutes to killmost weed seeds. A weed barrier of 2- to4-mL black plastic with holes made forplacement of plant plugs or seeds cangreatly reduce the need for weeding.Unfortunately, the black plastic tends tocause the soil temperatures to rise, whichwill affect the quality of the larkspurcrop. A light layer of leaves or bark canbe laid over the black plastic to reducethe heat buildup.

Another option for weed control is touse organic mulch as a surface applica-tion. If seeding is done in the fall, a 1-inch organic mulch layer (compostedleaves or grass clippings) can be appliedclose to the plants after they germinate.The mulch layer will reduce germinationof fall-germinating weeds. In the spring,if the organic mulch layer has thinnedout, an additional 1-inch layer can beplaced on the soil to reduce germinationof spring-germinating weeds.

A chemical option to prevent annualweeds from germinating would be toapply a preemergent herbicide. The pre-

emergents must be applied after the lark-spur seed germinates to prevent inhibit oflarkspur germination. If plants are estab-lished in the fall, preemergent herbicidescan be applied to weed-free soil aroundgrowing plants in the spring to controlspring-germinating annual weeds. Thepreemergent Dacthal prevents germina-tion of several annual weed grasses and afew broadleaf annual weeds. The preemer-gent Pennant is effective against annualgrasses, yellow nutsedge, and severalbroadleaf annual weeds. Check with yourlocal Cooperative Extension Service forcurrent recommendations on other pre-emergent herbicides labeled for use infield-produced cut flowers.

Glyphosphate (sold under severalbrand names, including Round-up) canprovide postemergent control of grassesand broadleaf weeds. Apply a 33 percentGlyphosphate solution with a wick appli-cator. Use extreme caution with this solu-tion. Be careful not to make contact withthe larkspur or the Glyphosphate will killyour desired plants as well as the weeds.

Some growers have used methyl bro-mide to fumigate the soil before directseeding of larkspur. Used for years, thissoil fumigant kills weeds, seeds, andmany insect and disease species. It ispresently still available for use by certifiedpesticide applicators, but is being phasedout of the market because it is extremelytoxic. Basamid (granular formulation) canalso be used as a soil fumigant and ismuch safer than methyl bromide.

Harvesting LarkspurFresh market sales

Larkspur flowers start opening from thebottom and progressively open up fromthe flower stem to the top. For fresh mar-ket sales, harvest when several lower

The fungus Rhizoctonia solani can alsocause damping off and seedling blight.Usually Rhizoctonia is favored by warmconditions. When compared to Pythium,Rhizoctonia lesions are more defined, withtan, sunken areas. Sometimes the lighttan, fine “cob web” mycelium ofRhizoctonia can be seen on blighted plantparts and growing across the soil surface.

To differentiate Pythium fromRhizoctonia, use an Alert on-site diagnos-tic kit. This will permit you to select thecorrect fungicide for control.

Basic good horticultural practices, sani-tation, and providing optimum condi-tions for seed germination and seedlinggrowth can prevent most damping-offlosses. Selecting a well draining mediaand watering early in the day so soildrains well before nightfall helps controlPythium. SoilGard, a biological fungicide,can be added to media to provide excel-lent control of both Pythium andRhizoctonia.

Botrytis blightsBotrytis can attack seedlings, but it is

especially damaging when it spots andblights flowers. High humidity and a filmof water on plant surfaces is necessary forBotrytis to infect plant tissues. Thus, anycultural practice that reduces periods ofleaf wetness (trickle irrigation, plant spac-ing to improve air circulation, use of hor-izontal air flow fans in greenhouses, etc.)will reduce the risk of Botrytis.

Botrytis produces a small, defined spotthat may rapidly enlarge to blight theflower, leaf, or stem. Weak plant tissuessuch as yellowing senescent foliage,flower petals, and wounds are easilyinvaded by Botrytis. Under humid condi-tions a gray mold is produced on blightedtissues. This gray mold is diagnostic ofBotrytis. Look for this aerial gray moldearly in the morning or incubate dam-

aged tissues in a moist chamber overnightto promote the formation of spores.

The Botrytis fungus has developedresistance to several major classes ofchemical fungicides, including the benz-imidazoles (e.g., Cleary’s 3336 andDomain) and the dicarboximides (Chipco26019), making chemical control diffi-cult. When extended periods of wet over-cast weather occur, it may be helpful tospray with mancozeb or use ExothermTermil smoke in the greenhouse. The cop-per fungicide Phyton 27 is also registeredfor Botrytis control on flowers.

Powdery mildewSome larkspur cultivars are susceptible

to powdery mildew caused by the fungusErysiphe polygoni. Symptoms includetwisted and distorted foliage and whitespots and patches on foliage, stems, andbuds. Flower buds may fail to open andflowers may be distorted and unsalable.Weather conditions that favor powderymildew are sunny, warm, dry days, andcool nights.

Several systemic fungicides (e.g.,Funginex, Terraguard, Strike, Banner) andsummer oil sprays all provide good con-trol of powdery mildew. Some larkspurcultivars are less susceptible. Keep goodrecords of disease incidence on each culti-var you grow; you can then select resis-tant cultivars.

Southern blightThe Southern blight fungus Sclerotium

rolfsii (also called Sclerotium delphini bysome authors) can be a serious problem infield-grown larkspur during hot weather.The fungus remains in the upper inchesof field soil and is only active during peri-ods of hot weather when soil tempera-tures rise into the upper 70s. The fungusattacks the plant at the soil surface, caus-ing a rapid wilt and crown rot of individ-

Cultivars•Consolida orientalis:

Giant Imperial series—The standardof the industry. Plants grow 3 to 4feet tall. Colors: carmine, deep blue,deep rose, light blue, lilac, pink,salmon, and white.Messenger series—Plants are 3 to 4feet tall and flower 2 weeks earlierthan the Giant Imperial series.Colors: Blue, lilac, rose, and white.Early Bird series—Earlybird flowers2 to 3 weeks earlier than GiantImperial. Plants are 3 to 4 feet tall.Colors: blue, lilac, rose, white, andmixed.QIS series—Very uniform plants andthick stems. Plants grow 2 to 3 feettall. Colors: carmine, dark blue, lightpink, lilac, rose, white, and mixed.

Pests

Major DiseasesThe most important diseases of lark-

spur cut flower production are damp-ing off of seedlings (Pythium andRhizoctonia fungi), Botrytis, powderymildew, and Southern blight.

Damping off and seedling rootrots

Several species of the water moldPythium attack larkspur seedlings. Bothcool and warm temperature species arereported. Wet conditions favor Pythiumdiseases. Pythium may rot the germinat-ing seed (preemergence damping off), orcause root rot that stunts or killsseedlings (postemergence damping off).Pythium produces a tan, water-soakedappearance in roots and stem. The rootcortex may slough off leaving the whiteroot vascular cylinder exposed, like finewhite threads.

the flowers by hanging flower stemsupside down and drying at 70 to 80 °F for10 to 14 days. A well-ventilated dryingbarn is ideal for preserving larkspur.

Postproduction Factors

Retail handling• Recut stems. After bringing larkspur

in from the field, recut stems underwater to prevent a water uptakeblockage.

• Ethylene. Flowers are highly sensi-tive to ethylene, with resulting pre-mature dropping of flowers. Flowerswill react when exposed to ethyleneat 3 ppm for 24 hours at 70 °F.Causes include shipping with mixed-fruit or decaying plant material.

blooms have fully opened. If shipping theflowers, try to harvest before the lowerone-third of the flower stem has opened.For direct markets, you may choose toharvest when one-half to three-quartersof the flower stem has opened. The vaselife of larkspur is between 5 to 7 days.The flower blooms are highly sensitive toethylene and will shatter in its presence.To hold larkspur for 1 to 2 days, placestems in fresh water, keeping themupright and maintaining temperatures of34 to 40 °F.

Everlasting salesLarkspur are relatively easy to dry for

sale as everlasting flowers. For everlastingflowers, harvest when the majority of theflowers have opened, but before the bot-tom flower petals have dropped.The feathery foliage does notneed to be removed when dry-ing the flower stems. Air dry

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• Pretreatment. Pulse with silver thio-sulfate (STS) to minimize ethylenedamage and prolong vase life. Use acommercial silver solution accordingto label directions, preferably for a 1-to 2-hour treatment. The STS solu-tion must be processed for silverrecovery before it can be disposed ofdown a drain. Commercial devices,such as a Superbatcher, are speciallydesigned to remove the silver fromSTS. STS is not very stable, giving thesolution a relatively short shelf life.Unfortunately, it is not always easyto determine whether your STS solu-tion is still active. Test kits are avail-able to test the solution’s effective-ness.

• Hydration. Hydrate in clean, warmwater (80 to 90 °F) at pH 3.5 to 4.0.

• Preservation. Use a floral preserva-tive for maximum longevity.

• Temperature. Refrigerate at 35 to 40 °F.

devices that monitor soil moisture andcan be used to help the grower decidewhen to irrigate. (For more information,refer to University of Maryland ExtensionService Bulletin 312, ”Soil MoistureSensors for Irrigation Management.”)

NutritionAdding a 1- to 2-inch layer of compost-

ed organic material and tilling it in willgreatly benefit larkspur growth. Larkspurplants also respond favorably to applica-tions of nitrogen fertilizer. If using trickleirrigation, fertilize on a weekly basis with100 parts per million (ppm) of completefertilizer based on nitrogen. Water-drivenfertilizer injectors are available that addthe correct proportion of concentratedsoluble into the irrigation water. If pro-ducing larkspur without trickle irrigation,side dress with a complete fertilizer (10-5-10 or 10-6-4 ratio) at 1 pound per 100square feet of production row.

Greenhouse ProductionLarkspur is best grown in groundbeds

to facilitate production and harvesting.The seeds should be sown fromSeptember through November. Maintaintemperatures at 50 to 55 °F for 8 to 10weeks. Raise temperatures to 55 to 60 °Fafter this time. Larkspur needs daylengths of 16 hours to flower. The daylength can be extended with lighting orwith 2-hour night break lighting usingincandescent lamps.

NutritionGreenhouse-grown larkspur needs

weekly applications of a dilute solublecomplete fertilizer (for example, 20-10-20or 15-5-15 ratio) at 100-200 ppm basedon nitrogen.

tures below 55 °F for 4 to 6 weeks beforebeing moved into the field in April.Yields of cut flowers seed-started in green-houses are generally not as heavy asyields from plants field-started in the fall.

Site selectionSelect a location that receives at least 8

hours of direct sunlight. A source ofwater near the site is good because an irri-gation system is frequently needed forbest quality production. Larkspur growsbest in well-drained soil with a pH of 6.0to 7.0. Using a raised bed improvesdrainage and will also warm the bed earli-er in the spring. Wide spacing of 10 to 12inches between plants will provide morecut flower stems per plant. The yield persquare foot will increase with a closerspacing of 4 to 5 inches between plants,but will decrease per individual plant.

SupportMost larkspur cultivars grow to a

height of 3 to 4 feet. Unsupported flowerswill often fall over with the stems turningupward. To maintain the quality of cutflowers, one or two layers of net or wiresupport (6- to 8-inch openings) are rec-ommended to help hold flowers upright.

IrrigationInstalling a trickle irrigation system is a

worthwhile investment. Irrigation is bestachieved using irrigation rowcrop tape orrowcrop emitter tubing that lies downthe row with emitters spaced 6 to 12inches apart. Two or three rowcrop tapeson a raised bed will water several rows ofplants across the bed. Coarse soils needmore tapes. Water frequently enough tomaintain a good soil moisture. Use ascreen filter of 100 to 140 mesh to pre-vent clogging and use a small pressureregulating device set at 8 to 10 psi toensure the proper operating pressure forthe trickle tubing. Tensiometers are

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established in the fall grow rapidly incool, moist springs, with heavy flowerproduction in May and June and occa-sionally into July if the weather remainsfavorable.

The genus of larkspur was recentlychanged from Delphinium to Consolida.Two species of larkspur are used for cutflowers: Consolida ambigua and Consolidaorientalis. C. orientalis is more uprightthan C. ambigua, and colors are oftenshades of bright pink and purple. C.ambigua have more branches initially andcolors are usually light pink or blue. Mostof the outstanding larkspurs for cutflower production are C. orientalis vari-eties.

Culture

Field Production

PropagationLarkspur is commonly produced by

direct seeding into the field. Somegrowers start or purchaseseedlings grown in greenhouseplug trays, and transplant lark-spur plugs into the field orgreenhouse growing beds.

Larkspur has a reputationfor poor germination. Seedsthat germinate best arethose planted 4 to 6months after harvest.Seed 1 year or older oftenhas germination rates ofless than 50 percent.Stored seed should berefrigerated until need-ed, but held for under 1year. An ounce of seedyields approximately 5,000plants.

2 11

Larkspur seed does not germinate wellwhen soil temperatures are held above 75 °F. Germination will be improved bychilling seed (35 to 40 °F) for at least 7 to14 days prior to planting. In Maryland,optimum seeding times for field produc-tion are from September through heavyfrost. Most growers will plant a series ofsequence plantings at 2-week intervals.Germination takes place 12 to 20 daysafter sowing. Once the seed has germinat-ed, the larkspur plants will grow rapidlyin cool fall weather. Larkspur plants plant-ed in fall flower 4 to 6 months after plant-ing.

An alterna-tive is to start

seeds in a green-house during the

winter and trans-plant the plugs in

early spring. Forgreenhouse growing, use

a germination temperature of70 °F, with a light covering of coarse

vermiculite. Transplants from the green-house should be conditioned at tempera-

Summary• Select larkspur cultivars and site.• For field production, prepare

seed beds in the fall and plant aseries of sequence plantings at 2-week intervals.

• Grow plants in full sun, prefer-ably in raised bedswith trickle irriga-tion.

• Monitor for aphidsand cyclamenmites.

• Monitor for dis-eased plants andpromptly removethose that areinfected.

Consumer Care

• Recut stems under water and placeflowers in clean warm water contain-ing a floral preservative.

• Avoid temperature extremes such asfreezing or temperatures over 95 °F.

• Keep flowers away from rapid airmovement.

• Avoid keeping flowers near ripeningfruit, which emits ethylene.

Stanton Gillregional Extension specialist

Central Maryland Research and Education Center

Ethel Dutkyplant pathologist

Department of EntomologyUniversity of Maryland at College Park

Russell Balgeregional Extension specialist

Western Maryland Research and Education Center

Tom Blessingtonregional Extension specialist

Central Maryland Research and Education Center

David RossExtension agricultural engineer

Department of Biological Resources EngineeringUniversity of Maryland at College Park

Bryan Butlerfaculty Extension assistant

Carroll County

Ginny Rosenkranzfaculty Extension assistant

Wicomico and Worchester Counties

Suzanne Klickcommercial horticulture technician

Central Maryland Research and Education Center

IntroductionLarkspur, Consolida spp., are excellent

cut flowers—both for fresh and dried oreverlasting markets. Many cut flowers arepopular for short periods of time, oftenattracting public attention for less than 5years, then fading from demand. Themarket for good quality larkspur has beenstrong for many years, past the period of“fad flowers,” and it continues to stayrobust. The alluring flower shape, widerange of colors, and appealing foliage allcombine to make larkspur a popular, mar-ketable cut flower. The flowers tend to besomewhat fragile and relatively short-lived in the vase (under 7 days), makingproduction for local markets very appeal-ing.

Larkspur grow to their full potential inclimates with cool, moist summers.Growers must adopt practices that takeadvantage of the cooler seasons to suc-cessfully grow larkspur as a cut flowercrop in Maryland. Maryland growersoften establish sequence plantings oflarkspur during the cool weather ofSeptember through heavy frost. Plants

Producing Larkspur as Cut Flowers

Fact Sheet 713

P97

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ReferencesArmitage, Allan M. 1993. “Specialty

Cut Flowers.” Athens, GA: Varsity Press,Inc.

Gill, Stanton A. and J. Sanderson. 1997.“Ball Greenhouse Pest Identification andIPM Control.” (In press.)

Nau, Jim. 1995. “Ball PerennialManual: Propagation and Production.”Batavia, Illinois: Ball Publishing.

Powell, Charles and Richard Linguist.1992. “Ball Pest and Disease Manual:Disease, Insect, and Mite Control onFlower and Foliage Crops.” Batavia,Illinois: Ball Publishing.

Woods, Christopher. 1992.“Encyclopedia of Perennials.” New YorkCity: Facts on File, Inc.

Reviewed byDr. John Dole, Oklahoma State

UniversityDr. Will Healy, George Ball Seed

Company, Inc.

Illustrations byRaymond Bosmans, Regional Specialist,CES Home and Garden Information

Center

Note: When trade names are included, no dis-crimination against similar products is intended.Mention of trademarks in this publication doesnot constitute an endorsement by the CooperativeExtension Service.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30,1914, in cooperation with the U.S. Department of Agriculture, University of Maryland at College Park,and local governments. Thomas A. Fretz, Director of Cooperative Extension Service, University of Maryland at College Park.

The University of Maryland is equal opportunity. The University’s policies, programs, and activities are in conformance with pertinent Federal and State laws and regulations onnondiscrimination regarding race, color, religion, age, national origin, sex, and disability. Inquiries regarding compliance with Title VI of the Civil Rights Act of 1964, as amended; TitleIX of the Educational Amendments; Section 504 of the Rehabilitation Act of 1973; and the Americans With Disabilities Act of 1990; or related legal requirements should be directed tothe Director of Personnel/Human Relations, Office of the Dean, College of Agriculture and Natural Resources, Symons Hall, College Park, MD 20742.