INSECT AND MITE PEST MANAGEMENT FOR

N.C. Flower Growers 2

INSECT AND MITE PEST MANAGEMENT FOR

POINSETTIAS

James R. Baker, Extension Entomologist

Integrated pest management is a pestcontrol scheme which uses a variety ofmanagement tools in addition to pesticides. In areal integrated pest management program,diseases, weeds, and plant growth areconsideredas well as insects and mites. IPM is a complexprogram as each crop must be consideredindividually. Fortunately, poinsettia is a cropwhich is amenable to IPM for several reasons.

Poinsettias have relatively few insect and mitepests. Poinsettias are not grown year round sothere is a break in the production cycle. This isa discussion of the insect and mite managementpractices of an IPM program for poinsettias.

Clothing

Avoid carrying insects into thegreenhouse by not wearing white, blue, yellowor green clothing. Aphids, thrips and whitefliesare attracted to yellow, green and blue. Thripsare also attracted to white.

Quarantine

Inquire of your supplier if he is havingwhitefly or mealybug problems. At least thenyou will know what to expect. In addition,inspect all plantmaterialbefore bringingit intothe greenhouse. Keep new plant material in aseparate section for a week or more beforeincorporating new material into the productionarea. Highly resistant thrips, aphids andwhitefliesarereadily transported throughout thegreenhouse industryon cuttings andplants.

Screening

Screening can significantly reducenumbersofinsects flying into greenhouses. Eventhripsareexcluded by severalscreeningmaterialson the market. A word of caution: the finer the

screen,the greaterthe resistance to air flow intothe greenhouse. To compensate, the growermust make the area of the screening materialstwo to eight time greaterthan the cooling padsorairinlets to the greenhouse. Polyspun (tobaccocanvas)requiresanareatwo times the areaofthecooling pads. Vispore 400 requiresanarea fivetimes as large. Vispore 1600 screening requiresat least 7 1/2 times as large a screen as coolingpad opening!

Monitoring

Constant vigilance for insects, mites anddiseaseisrequiredforeffective pest management.Assign certain employees the responsibility ofscouting for insects and other pests on a regularbasis (weekly the winter and twice weekly insummer). Keep written records ofwhere variouspests are found. Monitor pests by using yellowsticky cards, yellow pan traps, and by examiningthe foliage and occasionally the roots.

Record Keeping

Keep a log of pest type, locality,abundance and all pesticides applied. Theserecordscanbeoflong term benefit asmanypeststend to appear about the same time each year.Short term benefits include knowing what pests

survive a pesticide application. This can alertyou to the possibility of poor timing, poorapplication of the treatment, or pesticideresistance in the pest population. A change inthe kind of treatment or pesticide can be madebefore the crop is significantiy damaged.

Biological Control

Biologicalcontrolorganismscanbeusedin a pest management scheme for poinsettias,especiallyforcaterpillarandspidermitecontrol.Bacillus thuringiensis will control caterpillarson poinsettia and can be used with regularchemical pesticides. Predaceous mites areavailable to control spidermites, but thegrowermust refrain from using other syntheticinsecticides while using the predaceous mites.Encarsiaformosa parasitic wasps can be usedtocontrol the greenhouse whitefly, but againsynthetic pesticides cannot be used at the sametime. Insecticidal soap canbeused inconjunctionwith Encarsia wasps if the soap isapplied whenthe parasites are in the "black scale" stage.

Pest Recognition

It is important to be able to recognize thedifferent pests in all stages of development. Themost mixed up pests are shore flies and fungusgnats. Shore flies breed in algae and do littledirect damage topoinsettias (If plants are infestedwith Pythium, it is possible for shore flies tospread the disease around in the greenhouse.)However, shore flies are very resistant topesticides. Fungus gnats breed in decaying rootsand overwateredpeat moss. Fungus gnats can bevery damaging to poinsettia cuttings and plants,but fungus gnats can be controlledwith pesticides.Another common mistake is to assume that

parasitized aphids are a new kind of tan aphidwhich cannot be killed with insecticides.

Unfortunately pesticides are sometimesexpended uselessly against shore flies andparasitized aphids.

N.C. Flower Growers Page 13

Shore Flies are small (2mm), blackflieswith reddish eyesandspottedgraywings (Figure1). Shoreflies resembleeye gnats, fruit flies orvinegar flies in general shape. Shore flies aresometimes confused with fungus gnats whichare about the same size andcolor. (Fungusgnatsare shapedmore like miniature mosquitoes andhaverelatively longlegs andantennae.) Neitheradult nor immature shore flies feed uponornamental plants. Thedamagecausedby shoreflies consists primarily in the excrement ("flyspecks") leftonthefoliage ofbeddingplantsandother ornamentals and the spread of Pythiumaphanidermatum from infected plants touninfected plants. Because shore flies are oftenconfused with fungus gnats, control efforts areoften wasted (fungus gnats may be harmful toplants but are relatively easy to control; shorefliesare harmlessbutarevery difficult to controlwith insecticides). Sometimes shore flies becomeso abundant in greenhouses that the sheernumbers offlies becomes a deterrent to customersbrowsing or even employees working.

Figure 1. Adult shorefly.

Shore flies are commonly found ingreenhouses where they breed in algae growingon the potting mix, pots, benches and floors.Females scatter eggs right on the surface of thepotting mix. The eggs hatch in 2 to 3 days. The


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J Cycocel or Bonzi applications may be needed to control shoot elongation on stock plants.Cycocelor Bonziapplications maybe neededto controlheighton finishedplants. Do not applyBonziafterOctober for after start of short days, if pullingblackcloth over the crop.

3Control temperatures using fan and pad cooling to help prevent bacterial soft rotSpray or fumigate asneeded forcontrol. Controlling relative humidity during autumn through evening ventilation can

help reduce the incidence of botrytis.*Apply substrate (growth medium) drenches, rotating chemicals with each application.

Fungicide sprays may be needed for control.Earwigsare a pest mainlyduringrooting of cuttings. DrenchinfestedOasiscubesfor control.


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Drenchor granular applications may be needed forcontrolof larvae; sprayforadults.Screen to exclude moths; pyrethroids effectively control larvae.

10 Primarily astock plant pest; thorough spray coverage isneeded for effective control.11 Resistant to pesticides; algae control is necessary to reduce shore fly populations.12 Spider mites are mainly ahot, dry weather pest.13 Screen toexclude adults; crop monitoring and correct timing of pesticides are essential for control.

Crop scouting andproper timingof pesticides are essential for effectivecontrol.15 Try to eradicate whiteflies prior to bract coloration.


larvae are found within the crust of algae andvery top layer ofpotting mix. The maggots feedon bacteria and yeasts as well as diatoms andflagellates growing on the surface of the pottingmix. The larvae mature in 3 to 6 days and pupateinside the skin of the last larval stage (this kindof pupa is called a puparium). The last larvalskin affords the relatively tender andcompletelyhelpless pupa protection from environmentalhazards (including insecticides). Some of thepupariaare found on top ofthe potting mix or arevery close to the surface. A new generation ofadult flies emerges 4 to 5 days later. The adultscrawl about on the surface of the potting mix, onthe plants or they fly about the pots and plants.The flies move and fly rapidly but generally stayclose to their breeding sites. The adults feedprimarily on diatoms and flagellates on thesurface of the potting mix, mats etc.

Fungus Gnats are slender withcomparatively long legs and antennae (Figure2). They are grayishblack and about 2.5 mm

PUPA

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ADULT

Figure 2. Fungus gnat life stages.

long. Fungus gnat maggots feed on the roots ofcarnations, Easter lilies, geraniums, peppers,poinsettias, and organic matter. They are alsopests of house plants. Damage first becomeapparent when plants lose their healthyappearance and wilt. Adult fungus gnats areusually noticed before injury caused by themaggots is apparent. Adults and larvae inhabitmoist, shady areas. Adults live about 1 week,during which time each femaledeposits 100to150eggs. Theyarelaidinstringsof3to40inthetopofthesoil,usually nearstemsofplants. Theyhatchwithin4 days in the greenhouse. Thereis

a tendencyfor the progeny ofeach female to beall one sex. The larvae begin feeding on the roothairsandrootsusuallyintheuppercmofmedium,working their way up the plantand into the stem;however,they also feedon anyorganic matterinthe soil. Being somewhatgregarious, the larvaeoften form clusters in the soil. They mature inabout 14days, after which they construct apupalcase, made of silk and debris, in the soil. Thepupalstagelastsabout3.5 days. The adultsareweak fliers, but they run rapidly on the soilsurface or may remain motionless.

Clean cultural practices and lack ofexcessive watering may help prevent fungusgnat infestations. Since fungus gnats preferpottingmixescontainingpeatmossandabundantmoisture, consider using bark mixes and avoidoverwateringornamental plants. Decoy pots ofsprouting grainare attractive to females, whichwill lay their eggs in thesepots. Afterwards, thepots should be submerged in boiling water or thecontents destroyed in some manner every 2weeks to destroy the eggs and maggots. Fungusgnats have few efficient natural enemies. Somespecies of fungus gnats in mushroom houses.have developed up to 47 fold resistance to apyrethroid insecticide.

Leaftiers are small caterpillars which tiethe leaves ofpointsettia togetherandfeed withinthe shelter thus formed. Two species ofleaf tiersare found on poinsettias in North Carolina, theobliquebanded leafroller and a leaf tier with nocommon name, Platynota flavedana.Obliquebanded leafroller adults are 1.7-3.3 cmdark deep yellow to reddishbrown moths withpale orangeyellow (males) to deep yellow(females) hind wings (Figure 3). Female mothsare larger than males. There are two broods ofobliquebanded leafrollers in North Carolina.Moths have been collected from late Aprilthrough October. The caterpillar is a smallgreenishwormwhich ties theleavesofpoinsettiatogetherand feeds within. Platynotaflavedanafemale mothsarereddish brown andfairlyevenlymarked. Males are blackish brown with

contrastingreddishocre tips ofthe wings. Thereare 2 to 3 broods of

Platynotaflavedana eachyear. Moths havebeen collected from

April to October.The slender

caterpillars aregreenish or

Figure 3. Adult ofoblique brownish (Figurebanded leafroller. 4) They tie the

leaves of poinsettia together with silk and feedwithin. Leaves that are notdirectly fed upon aredistorted because they grow unevenly becauseof the silk tying them together even after thecaterpillar has matured.

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Figure 4. Caterpillar ofPlatynota flavedana.

Mealybugs are small, soft, oval insectswithout wings (except for males). Some speciesare covered with fluffy wax and others havelong tails. Male mealybugs are tiny, gnatlikeinsects with two wings and long tails. With thosespecies of mealybug which lay eggs, the eggsare very small but are covered by a conspicuousdense, fluffy, white mass of wax called theovisac. Very young nymphs are flat, oval andyellow. Older nymphs of some species arecovered with fluffy, white wax. Mealybugs

N.C. Flower Growers Page17

Figure5. Citrusmealybugs onpoinsettia.

damage plants by inserting their thread-likemouthparts into any part of the plant, injectingsaliva, and sucking out sap. Mealybugs excretehoneydew, a sweet, sticky liquid. Sooty moldsoften grow in the honeydew causing infestedplants tobecomeblack. The citrus mealybughasa toxin in its saliva which causes its host plantsto drop leaves and buds. Small numbers ofmealybugs are easily overlooked as they tend towedge into crevices on plants (Figure 5). Afterthe first batch of eggs hatches, the mealybugsbecome more noticeable. As their numbers

increase, mealybugs of all sizes can be foundcrawling around or feeding on all surfaces of theplant. Each female usually lays from 200 to 600eggs. After several weeks, nymphs develop intoadults.

Mealybugs are not easy to control.Because the eggs are often protected in an ovisac,it is difficult to get a pesticide through the fluffywax to kill them. (This is one case where the useof a spreader sticker may be called for. Use anadjuvant with which you have experience or anadjuvantwhichisrecommendedbythecompanythat makes the pesticide you are using. Beforeusing a pesticide or pesticide/spreader


combination which is new to your program, besureto try it on a small number of plantsbeforetreating a large number.) Therefore it is veryimportantto "scout" plantsregularly in ordertodetectmealybugsbefore theirnumbersbuildupand the insects form their "nests" of wax and

eggs.

A predaceous insect, theAustralian ladybeetle, is commerciallyavailable should agrowerwant to incorporate biological control into hispest management program. However, theAustralian lady beetle cannot be obtained atcertain times. In addition, lady beetles aresomewhat sensitive to pesticides so the growerwouldhave to curtail oreliminate the use ofmost

pesticides.Sweetpotato whitefly has become a

majorpest of cotton in southern California andArizona due to a remarkable acquisition ofresistancetopesticides commonlyused forcottonpest suppression. In 1986 in Florida, thesweetpotato whitefly suddenly became agreenhousepestonpoinsettiaswhereitexhibitedextraordinary resistance to certain pesticides.

Sweetpotato whitefly eggs develop forabout six days. Tiny "crawlers" hatch and crawlabout until they insert threadlike mouthpartsinto the bottom of the leaf to feed. The crawler

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Figure 6. Sweetpotato whitefly lifestages.

molts into a scalelike insect (nymph) which alsosucksout sap (Figure 6). The nymph grows andmolts a second time and a few days later moltsinto athird nymph. The thirdnymph molts intothe fourth stage whicheventually ceases to feed.Inside the fourth nymphalskintheadultwhiteflydevelops. Adults emerge from the fourthnymphal skin through a T-shaped slit about amonth from the time the egg was laid. Femaleslive about two weeks and lay 28 to 300 eggseach. In very host weather, development maytake only two weeks and in cool weather,development maytake much longer. Except forslightly smaller size, slightly more yellowishcolorandthe tendency for the adultsto wrapthewings around their bodies a little tighter thanusual, adultsweetpotato whiteflies are difficulttodistinguish from manyotherwhiteflyspecies.There are other species of whiteflies whichsometimes infestornamentals in the greenhouse,but they are not as resistant to pesticides. Forexample, citrus whiteflies and bandedwingwhiteflies areoccasionallyfoundin greenhouses.Bandedwing whiteflies are apparently notresistant to pesticides and can be easilyeliminated. Citrus whiteflies are more difficult

to suppress.

Greenhouse whiteflies are consistendya major whitefly pest of greenhouse flowers.The greenhouse whitefly was first describedinEngland in 1856 and first recorded as agreenhouse pest in the United States in 1870.

Greenhouse whiteflies reproducerelatively slowly (1 generation each 30 to 45days). Each female may lay up to 400 eggs andmay live almost 2 months althoughmostprobablylive 30 to 40 days and lay 60 to 80 eggs (Figure7). Whiteflies are usually found on the lowersurface of new leaves. Here they insert eggswhich hatch into young called crawlers. Once itstarts to feed, the young whitefly probably doesnot change locations until the adult emergesabout 23 days later. Adults are pale green toyellow at first but soon secrete a white, waxybloom.

surrounded by a purplish-red margin.Occasionally, lesions coalesce resulting in thegirdling and death of stems. Brown spots uptoonecm appear on leaf blades. These are usuallyconcave on the upper surface giving the leaf apuckered appearance. Severely affected leavesdrop prematurely. A grayish-brown velvetylayer of fungal growth (spores) may be found inthedepressed spotsonstems. Conidia are spreadto healthyplants by splashing water.

Scab is a more common disease onpoinsettias grown outside in Florida than it isunder greenhouse production in North Carolina.Wild hostsoutsidethe production areas inFloridaare important sources of the pathogen.

Wet Rot. Wet rot causedby the fungusChoanephoracucurbitarum occurs on both stockplants andon cuttings under mist propagation.The pathogen is capable of killing plants in allstages of production.

The symptoms of wet rot on poinsettiaplants are a soft, wet, mushy decay of leaves,petioles and stems. If the stems are green andactively growing, they become soft, wet, flaccidandwilt ordroopbefore collapsing. If the stemsare somewhat woody, only necrosis occurs.Small plants and rooting cuttings may bedestroyed in only a few days when weatherconditionsarefavorable fordiseasedevelopment.Onlargemulti-stemmed stock plants,the fungusmay kill the plant stem by stem.

The pathogen usually sporulatesprofusely on diseased plant parts, especially onstems. The fungus produces single celledsporangiophores (stalks), each bearing a clusterofblack spores on the end. The sporangiophoresarelong andvery abundant, giving the appearanceof a coarse, hairy or "whiskery" growth. Thespores can be spread by water, wind, movementof plants (cuttings), hands, knives and insects.

Under North Carolina conditions, this is

primarily a disease of stock plants and cuttingsunder mist. This fungus attacks the flowers awide variety of plants including squash, okra,petunia and hibiscus.


Alternaria Blight or Leaf Spot Anewleafspotorblightdisease ofpoinsettiacausedbythe fungus Alternaria euphorbiicola was firstobservedin Florida in 1984. Symptoms of thisdisease can be confused with bacterial canker orscab. This disease has not been reported inNorth Carolina.

Leaf infections initially appear as 1 to 3mm diameter spots with tan centers, dark thinmargins and achlorotic halo. As spots enlarge,theyoften progressalonglateral leafveins. Spotsenlarge to form irregular necrotic lesions, 25mm across or larger. Leaves with several spotsbecome chlorotic and abscise.

Spores of Alternaria euphorbiicola areair-borne and can survive dry periods to causedisease when moisture becomes available.

Environmental conditionsinoutdoorproductionareas are morefavorable fordiseasedevelopmentthan greenhouseconditions, presumably becauseof frequent prolonged periods of leaf wetness.Outdoor production and wild host sources ofsporesmake this animportantdisease in Florida.It should be less important in North Carolinaifgrowers startwith disease-free plants and growthem in greenhouses using a watering systemthat keeps the foliage dry.

Diseases Caused bv Bacteria

Bacterial Canker. Bacterial canker is

caused by Corynebacterium poinsettiae. It isnot as wide spread today as in the past, probablydue to healthier rooted cuttings and use ofwatering systems that keep above ground plantparts dry.

The most prominent symptoms arewater-soaked areas on the lower stem or narrow water-

soaked streaks often extending severalcentimeters along branches. These lesions areassociated with exuded droplets oflatex that dryto form pale yellow or golden crusts. Infectedplants frequendy have malformed, small bracts,arestuntedandretarded slightly in development.Under conditions of low moisture, marginal


wilting of leaves has been observed. Severelydiseased branches maybe girdled anddie. Plantsmay grow out of visible symptoms yet retaininternallow populationsofthe bacteria.Cuttingstaken from these plants frequently show diseasesymptoms in laterstagesofproduction. InNorthCarolina, this disease is often seen in late stagesof finishing.

The disease is spread by vegetativepropagation ofcuttings from apparently healthyplants. The bacteriacan also be spreadduringpinching, by infested irrigation water, and onknives when taking cuttings.

Bacterial SoftRot Soft rot caused by thebacteriaErwmiacarotovora andE. chrysanthemiis a common disease problem in North Carolinaduringandjust afterpropagation.These bacteriaare most likely to cause problems on succulenttissue, under hot wet conditions; wounded orbruised tissue is highly susceptible. Infectedtissue becomes water soaked, and develops intoa soft mushy rot. The disease can develop veryrapidlyon cuttingsundermist Afterpropagation,Erwinia chrysanthemicauseschlorotic spots thatrapidlycoalescefonninglargeirregularchloroticareas. Petioles turned black, shrivel and

associated leaves wilt within a few hours.

Chlorotic areas turned black, stems collapse andaffected tissues become soft and water soaked.

Greasy CankerorBacterial Stem Canker.

Greasy canker caused by the bacteriaPseudomonasviridaflava has beenreported fromCalifornia and Florida. This bacterial disease

appears as rapidly advancing oily or greasycanker associated with pruning wounds. Leafspotbractandbud blight have alsobeen observed.

This disease occurs at all temperatures aslong as the relative humidity is high. Diseaseseverity increases at higher temperatures (27-32°C or 80-90°F). Disease progressis arrestedwhen relative humidity is reduced; infectedtissue then becomes tan to brown and papery.

Control of Poinsettia Diseases.

Control of poinsettia diseases requires atotal program starting withgoodplanning beforethe plants arrive at the greenhouse andendwithclean up afterthe lastplant hasbeensold. Stepsin apoinsettia disease control program include:1. Do not carry any. plants over from one

season to the next.

2. Clean all benches where poinsettias willbe grown.

3. Have cleanpots andmedia available forpotting.

4. Try to avoidany unnecessary woundingor bruising of the plants.

5. Purchase plants or cuttings from areputable supplier.

6. Inspect the plants on arrival for anyproblems.

7. Try to grow plants as close to optimumconditions aspossible to minimize stress.

8. Keep the relative humidity below 85%whenever possible.

9. Maintain temperatures below 90-95°Fwhenever possible.

10. Use a watering system that keeps thefoliage dry.

11. Space plants properly to promote goodair movement between the plants.

12. Have good horizontal airmovementoverthe crop.

13. Try to prevent condensation on the plantsurface during the night.

14. Chemical protection:(a) fungicides can help prevent root rotdiseases and Botrytis blight(b) drench with the proper combinationof fungicides on a preventative programfor root rot (see Table 2)(c) repeat fungicide drenches monthlyfor root rot control

(d) use sprays or fumigate as needed tocontrol Botrytis blight(e) alternate fungicides for Botrytiscontrol to avoid resistance.

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