North Carolina

Flower Growers5

BulletinVolume 51, Number 3&4

June and August 2006

N.C. Commercial Flower

Growers Association

$4.00

Official Publication of the North Carolina Commercial Flower Growers' Association

Calcium Deficiency Disorders in Poinsettias

W. Roland Leatherwood and John Dole

North Carolina State University

Poinsettias are the top selling potted flowering plantin the United States and Europe. Their history in theUnited States begins with Joel Poinsett, the U.S.Envoy to Mexico from 1825 to 1830. Poinsettintroduced poinsettias to America in 1825, which, ofcourse, led to the common name, poinsettia. Thepoinsettia was formally named Euphorbiapulcherkma by Karl Ludwig Willdenow, head ofthebotanical gardens in Berlin, and was scientificallydescribed by his custodian Johann Friedrich Klotzschin 1834. In the United States poinsettias were initiallymarketed as cut flowers and it was not until the early1900's that the first pot varieties were selected. In2005, wholesale poinsettia sales in the United Statestotaled more than $242 million and numbered more

than 59 million pots, according to the U.S. Departmentof Agriculture. North Carolina is the second greatestproducer of poinsettias, with California first.

Popularity and history do not change the basicnutritional challenges faced in producing poinsettiasas a greenhouse pot crop. Though research has beenongoing since the 1940's, much work remains to bedone to resolve the unique nutritional problemsassociated with this high value crop. Calcium (Ca2+)deficiency in particular is associated with severalmetabolic disorders in poinsettias such as bractnecrosis, leaf edge burn and lateral stem weakness.Bract necrosis (BN) and leaf edge burn (LEB) are

both characterized by black or brown necrotic spotsor patches along the edges of bracts or leaves. Thesespots can coalesce until the entire margin is necrotic,which is then easily attacked by Botrytis causingfurther damage. Lack of stem strength is problemduring shipping for many varieties and can beaggravated by poor nutrition and growing conditions.When trying to prevent and correct calcium problemsit's good to understand how calcium moves inpoinsettias.

Calcium has important roles in cellular signallingand strengthening cell walls, so deficiencies willresult in weaker tissues. It is transported by watermovement in the xylem and thus requires transpirationto reach young leaves and bracts. High relative

Leaf Edge Burn

Photo: B. Whipker

(Continued on page 4)

N.C. Flower Growers' Bulletin - June and August 2006

• humidity, low temperatures, poor air circulation orany othercondition that reduces transpiration reducesuptake of water, and therefore calcium content.Additionally, several soil chemistry factors limitCa2+ availability such as high EC, unbalancednutrition, low pH and low Ca2+ concentration.Ongoing research has found that though calciumdeficiency plays central role in BN, LEB and stemweakness, simply increasing amounts of availablecalcium may not help very much.

Bract Necrosis and Leaf Edge Burn. Most crops inproduction greenhouses are supplied more nutrientsthan required forsatisfactory growth (known as luxuryconsumption). For many crops this strategy worksquite well, but with poinsettias excess nutrition,particularly late in the season, creates problems. Therelationship between BN, LEB, nitrogen (N),potassium (K) and Ca2+ must be kept in mind. Bractnecrosis is associated with Ca2+ deficit as bracts have

reduced stomatal density and very low rates oftranspiration. Therefore, bracts take up Ca2+ slowlyso even a slightly low Ca2+ contents may causeproblems. In fact, bracts account for only 0.1 to 0.5%of the total Ca2+ transported to the whole shoot andmost of that is transported during the very earlystages of growth. Since Ca2+ in the bracts is mostlytransported in early development, a luxuriant supplyof Ca2+ in combination with lower K and/or N duringearly growth may increase the final Ca2+ content ofthe bracts.

Another approach to preventing BN is to maintain aslight K+ deficiency, which results in a greater Ca2+content in the bracts and the whole plant withoutdegrading quality. This relationshiop is to beexpectedgiven the known Ca2+ - K+ antagonism. Moresurprising, however, is that the Ca2+ concentrationwill also be higher in bracts of plants grown underslight N deficiency than plants with ample N. Nitrogen

deficiencyprompts theproliferation ofyoung root tips,which are known

to be the site of

Ca2+uptake. Asaresult, plantsunder slight Ndeficit have a

greater ability toPhoto: W. Roland Leatherwood absorb ca|cium.

Volume 51, Number 3&4

Plants grown under slightly reduced N, K, or alteredN:K regimes will be similar in size, and havecomparable number and size of bracts compared toplants with raised with 'luxury consumption'nutritional availability, but have less incidence ofbract necrosis during the postharvest period.

Poinsettias grown under high N availability have ahigh growth rate and a decreased root:shoot ratio.The resulting plants have a shorter postharvest life,increased leaf and cyathia abscission, and greaterincidence of bract necrosis. Accordingly, under highgrowth rates, Ca2+ is most deficient at the bract andleaf edges, the location where bract necrosis and leafedge burn start. High growth rates exceed the plant'sability to supply enough Ca2+ to distal parts. Similarproblems from N induced high growth rates are seenin other crops. Incidence of blossom end rot oftomato, lettuce tip burn, and apple bitter pit are alldirectly related to tissue growth rate and calciumdeficiency in distal tissues.

To avoid many of the problems associated with Ca2+deficiency growers should use several approaches.Reduce fertility rates and watering during the finalweeks of production and if possible, use water onlythe last two weeks. Keep in mind when using slowrelease fertilizers that they should be mostly dispersedby the time the last few weeks of the crop cycle comesaround. In any case, do not apply new fertilizers ofany kind towards the end of the production cycle.Maintain low humidity and high air circulation in thegreenhouse to increase transpiration. Growers shouldmonitor calcium amounts in soil and tissues

throughout the crop cycle. If either test indicates lowCa2+, then weekly 200 - 400 ppm CaCl, sprays (Table1) from first color to the delivery week will helpcounteract the problem. Be sure to use reagent gradeCaCl, as horticultural grade contains impurities thatmay damage the bracts. Anhydrous and dihydrateforms are available. The dihydrate form is usuallyless expensive (Fischer Scientific Cat.# S75070).Also, use a spreader sticker during application andapply as a fine mist just until the bracts or leavesglisten.

At the end of the crop cycle, growers often lowertemperatures to hold plants for sale, aggravating BNand LEB. Low temperatures and high soil moistureresult in low water movement through the plant.Calcium concentrations continue to drop in bracts asthe plant ages. Timing of the crop and production •

N.C. Flower Growers' Bulletin - June and August2006

^ cycle can help minimize the amount of time thatplants are held in unfavorable conditions.

Stem Breakage. During shipping, poinsettias mustbe able to withstand a greater degree of mechanicalstress than found in the greenhouse. Stem breakageresults in loss of salable plants and has a directcorrelation with calcium deficiency. Nitrogen tooplays a role. Experimentally, poinsettias grown with75 mg L1 N have greater lateral strength than thosegrown at 125 mg L"1 N. Also, plants grown witheither 15:2:20 or 15:5:15 NPK had significantlystronger stems than those grown with 20:10:20 NPKat both rates. In each case, lower N resulted instronger laterals and plants with equal appearancecompared those provided complete nutrition. Stemstrength can be improved with direct application ofCa2+ as a spray or as supplemental liquid feed. Plantsfertilized with NH4N03 andCa(N03), have strongerstems compared to those receiving no additionalcalcium. To help strengthen stems, growers canapply a 300 ppm CaCl, spray as described above, ifindicated by soil and foliage test. However, thetreatment is less effective on self-branching culti vars.

There are other methods to reduce stem breakage.Increasing light levels to above 3,000 foot candles inthe period before short days, adding ring supports topots and stronger cultivars are common approaches.Use of thicker cuttings, up to 7 mm in diameter,reducing the number of laterals by pinching to 4 to 5nodes, and increasing spacing also help. Spacing isperhaps the trickiest method to understand here.Because plants grown at bench edges will have morehorizontal branches they are more likely to breakduring sleaving. However, spaced too closelybranches become thinner and weaker. The goal isspacing that will produce a large branch angle anddiameter, but not such that there will be a problemduring sleaving. To get there, allow a few days afterthe canopy closes before spacing.

Volume 51, Number 3&4

numbersof cuttings are produced rapidly,the plants'ability to take up Ca2+ is pushed to the limit. Sincepoinsettias are already poor at Ca2+ distribution,situations involving rapid growth, such as cuttingproduction, are likely to result in Ca2+ deficiencies.Equally important, Botrytis spores can infect thesenecrotic areas and subsequently travel on cuttingsharvestedfrom infected stock plants. These cuttingsare much more likely to develop disease problemsduring shipping or propagation.

In the case of stock plants, ammonical N in anyamount greatly increases leaf edge burn so favornitrate fertilizers suchas Ca(NO,),. However, someammonium is needed too, so don't apply nitratefertilizers exclusively. Leafedgeburnisdramaticallyreduced when 500 ppm Ca2+ is applied as a foliarspray rather than soil applied. Appropriatemanagement of N availability and source, reductionof K availability, and increasing supplemental Ca2+will go a long way to resolving most Ca2+ disordersgrowers encounter with poinsettias, resulting in robustand long lasting crops.

So what can you do this fall to prevent Ca2+ relateddisorders? Several simple steps can be taken. Fromthe first week of color to delivery apply 200 to 400ppm CaCl, spray as directed above. Stop or sharplyreduce fertilization during the final weeks ofproduction. Make efforts to reduce humidity andincrease air circulation during the crop cycle.Overfeeding can lead to nutrient antagonisms andrapid weak growth, so keep the plants on a strict'diet'. Also, favor nitrate fertilizers a little more thanwithothercrops. Finally,contactyourcuttingsupplierto find out which varieties are susceptible to LEB orstem breakage. There may be more resilientalternatives available.

Stock Plant Management.Proper Ca2+ nutrition forpoinsettias is not limited tothe production environment,but is a concern before

cuttings are ever taken.Poinsettia stock plants aresusceptible to LEB duringperiods of high productivityand rapid growth. When large

Table 1. Dilution Table for Calcium Solutions

Amount of Final Spray SolutionCalcium Chloride DihydrateCaCl, 2H.O (-27% Calcium)

Calcium Chloride AnhydrousCaCl,

(-39% Calcium)

100 gallon 1 lb. 12 oz.

25 gallon 4 oz. 3 oz.

3 gallon 1/2 oz. 3/8 oz.

Approximate ppm Calcium 324 ppm 357 ppm

Source: Paul Ecke Ranch. ©1999 Paul Ecke Ranch All Rights Reserved

N.C. Flower Growers' Bulletin - June and August 2006

•" Rcfrcnccs

Bierman, P., J. Dole. C. Rosen, and H. Wilkins. 1989. Calciumdeficiency on poinsettia slock plants. Minnesota StateFlorists Bulletin 38:1-4.

Cox, E. F.. J. M. T. McKee. and A. S. Dearman. 1976. The effectofgrowth rate on tipburn occurrence in lettuce. J. Horl. Sci.51:297-309.

Ecke. P. 2004. The Ecke poinsettia manual. Ball Publishing.Batavia. 111.

Mo. L. C. R. I. Grange, and A. J. Picken. 1987. An analysis ofthe accumulation of water and dry matter in tomato fruit.Plant Cell Environ. 10:157-162. '

Klot/sch. J. F. 1834. Beschreibung zweier neuen Euphorbienaus Mexico. Allgemeine Gartenzeitung 2:26-28.

Kuehny. J. S.. P. C. Branch, and P. VV. Adams. 2000. Stemstrength of poinsettia. Proc. Acta Hort. 515:257-264.

Lawton. K. A.. G. L. McDaniel. and E. T. Graham. 1989.

Nitrogen source and calcium supplement affect stemstrength of poinsettia. HortScience 24:463-465.

Volume 51, Number 3&4

Marschner. H. 1995. Mineral Nutrition of Higher Plants. 2nd ed.Academic Press. London.

Starkey. K. R., and N. E. Andersson. 2000. Effects of light andnitrogen supply on the allocation of dry matter and calciumin poinsettia (Euphorbiapulcherrima Willd. ex Klotzsch).J. Hort. Sci. Biotechnol. 75:251-258.

Starkey. K. R.. and N. E. Nielsen. 2001. Reduced N and Kapplication increases Ihe uptake of Ca and improves thequality of poinsettia (Euphorbia pulcherrima Willd. ExKlotzsch). Proc. Plant nutrition: food security andsustainabilityofagro ecosystems through basic and appliedresearch 312-313.

Vang-Petersen. O. 1980. Calcium deficiency of 'Cox's Orange*apple trees during the fruit growth period. ScientiaHorticulturae 12:163-168.

Wissemeier. A. H.. and S. Marienfeld. 1998. Poinsettia

(Euphorbia pulcherrima Willd. ex Klotzsch) bracts:disadvantaged organs with respect to calcium nutrition.

Aneewandte Botanik 72:1-6.

Sii

Leafminers in Garden Mums

Christine CaseyNorth Carolina State University, Department of Entomology

Leafminers are one of the most challenging pests tocontrol during production of garden mums, largelybecause growers don't realize they are present untilthe damage is observed. At that point the damage isdone and it is too late for effective control.

The female leafmincr deposits her eggs into leaves,leaving small brown puncture wounds that may be

mistaken for a

disease, anotherreason whygrowers might missthis pest. As thelarvae develop,they feed insidethe leaf, creatinga disfiguring,serpentine-shaped mine.

Examine favored plants such as chrysanthemumsand gcrbera regularly for leaf punctures and smallmines. Use yellow sticky traps to detect the adults,which arc about 3/16 inch long and have yellow andblack bodies with large red eyes. Under greenhouseconditions a new generation occurs every two to

three weeks; watch for increasing number of adultson sticky cards as an alert that this is happening.

Leafminers tend to readily develop resistance topesticides that arc routinely used against them, sorotation of products is essential. Avid is a goodleafmincr product, as are some of the insect growthregulators such as Citation or Azatin. GranularMarathon is also labeled but is an expensive option.Conserve is also labeled but I think it is preferable tosave this material for thrips. If you use Avid forleafmincr control avoid its use against spider mites.

Recognizing flies on sticky cards

Resemblance

FungUS ::n;il Shore fly Leafminer

Tiny mosquito Small house flyFruit fly. except

yellow

Legs and

antennaelong short short

LarvaClear to white; shiny

black head

Clear lo white; no

head capsule: forkedair lube at posterior

Yellow with no head

capsule

WingsClear wiih a distinct

Y-shaped veinFive white spots on

each grey wingTransparent

Preferred

hosts

Many different plants.soil organic material.

fungialgae

Chrysanthemum,gerbera