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pests & diseases

Whiteflies canbe difficultpests tom a n a g e ,especially in

greenhouses where they enjoy ahigh-quality food supply, favor-able environmental conditionsand minimal protection from nat-ural enemies. Whiteflies damagea number of crops: verbena, fuch-sia, regal geranium, lantana, nico-tiana, ageratum and of coursepoinsettia. Often, growers cansuccessfully control whiteflies allseason with effective foliar or sys-temic treatments applied early inproduction; however, sometimesthese fail, or uncontrolled popula-tions re-infest the crop from othersources. With the loss of Dithioand Plantfume smokes, growershave been wondering aboutwhitefly control options for late-stage poinsettia production. I amalso seeing annual problems withLewis mite, a relatively “new”pest of poinsettia, that often

becomes apparent in fall wellafter sprays would normally beapplied. Early symptoms of dam-age are very subtle and easilymissed. From a distance it may beeasily confused with a lack ofnitrogen. If treatments are neededto control either pest during thesensitive bract stage, which onesare likely to be safe for plants?

It might be helpful to reviewsome of the basic elements ofwhitefly management, since it isusually the primary pest in poin-settia production for most grow-ers. Good management early oncan carry the crop into color withminimal pest infestation andoften eliminates the need toapply any insecticides afterbracts form. Consider the follow-ing points when you evaluateyour operation:

• source(s) of infestation: wherethe whiteflies are coming from;

• correct identification: whichtwo common greenhouse speciesis/are present;

Late-Season

WhiteflyControl

By Daniel Gilrein

With the loss of Dithio and Plantfume smokes,Cornell University researches whitefly controloptions for late-season poinsettia production.

Whitefly image courtesy of USDA/ARS.

• a monitoring plan: detectpests early before infestationsare obvious;

• prevention: use cultural andnon-chemical controls to avoidinfestation; and

• effective treatments: whenneeded, select and time appro-priate insecticides or biologicalcontrols.

SOURCE(S) OFINFESTATION

It was clear from past work inour IPM program that growerswere often unaware of the sourcesof whitefly problems. Theseincluded older stock or “pet”plants kept around the green-house and weeds inside and out-side the range. Cutting-grownstarter plants (such as poinsettia)were sometimes infested onarrival, but often they were veryclean and contributed minimallyor not at all to the problem. Wefound whiteflies by checkingunder leaves of weeds inside andoutside the range, examininglower leaves on stock plants andother older plants around thefacility and inspecting new plantmaterial on arrival.

CORRECTIDENTIFICATION

While there are more than 1,200species of whiteflies identifiedworldwide, silverleaf whitefly(Bemisia argentifolii) and green-house whitefly (Trialeurodes vapo-rariorum) are the two most com-mon species in greenhouses.Distinguishing them is not too dif-ficult and is important for growersinterested in using biological con-trol. It can also help in tracing thesource of infestation. The easiestway to tell the difference is toexamine the pupal stage, justbefore the whiteflies emerge.Greenhouse whitefly pupae arewhitish, shaped similar to a cakewith vertical sides and have afringe of fine hairs around theedge. Silverleaf whitefly pupaetend to be yellowish, have amound shape and lack the fringeof hairs. These features are visible

under a hand lens, but if unsuresend a sample to a diagnostic labor entomologist for confirmation.

A MONITORING PLANSometimes businesses detect

infestations when already severe,often just as plants are ready forsale. Early detection can make allthe difference, enabling timelytreatment before populations arehigh. A combination of yellowsticky cards, placed vertically justabove the crop canopy, with regu-lar plant inspection, is a simpleway to detect whiteflies early. Placecards in areas of air movement andamong older plants where theinsects are likely to be found.Usually 1-3 cards is suggested per1,000 sq.ft., but if this seems liketoo many or impractical even a fewcards, thoughtfully placed, will beuseful. Check the cards weekly ifpossible, and keep a record ofwhiteflies trapped since the lastcheck. The cards also help to indi-cate activity of a few other pests,such as thrips and fungus gnats.

Sticky cards may not tell thefull story, since we have missedsome infestations by relying onthem too heavily; therefore, besure to examine the undersides ofolder leaves for whiteflies andtheir immature (nymph) stages. Ifinfested plants are found, flag afew with tape or stakes to re-check after controls are applied.

PREVENTIONTake care to avoid introducing

clean poinsettias or other plantsinto an infested environment.Isolate and treat infested material,and eliminate all other sources ofinfestation, including the weedsand “pet” plants identified whenmonitoring. In instances whereolder and younger plants need tobe put together in the same rangeor in houses with fans or otheractive airflow, locate clean plantsupwind of older plants. Somegreenhouses have eliminatedweedy borders around theperimeter, replacing with turf ormulch underlain by landscapefabric or other weed barrier.

EFFECTIVETREATMENTS

There are many productslabeled for control of whiteflies,including aerosols, sprays andsystemics. Many people useMarathon (Olympic HorticulturalProducts) media treatments, butthere are also reports of goodresults with foliar sprays such asTriStar (Cleary Chemical Corp.)and Flagship (SyngentaProfessional Products), two newerneonicotinoids. Distance (ValentUSA Corp.), an insect growth reg-

ulator (IGR), has shown goodresults in trials as well as in actualproduction settings, sprayingonce or perhaps twice relativelyearly in production before colorshows. It has translaminar activi-ty, as do some of the neonicoti-noid insecticides, so coveragemay not be quite as critical. Noteit should not be applied afterbract formation. Enstar II(Wellmark International) andAzatin (Olympic HorticulturalProducts) (Ornazin, SePRO Corp.,and Aza-Direct, Gowan ç

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Top: Silverleaf whitefly. (Photo courtesy of Ron Oetting) Bottom: Whiteflies onpoinsettia. (Photo courtesy of Jim Bethke)

Company, have the same activeingredient as Azatin) are otherIGRs that have worked well for ustoo. Apply weekly with goodfoliar coverage. Endeavor(Syngenta Professional Products),a relatively new product, hasshown good knockdown of adultsin our tests. Orthene/pyrethroid,which includes Tame (ValentU.S.A. Corporation), Talstar (FMCCorp.), Decathlon (OlympicHorticultural Products), Scimitar(Syngenta Professional Products),Mavrik (Wellmark International)and Astro (FMC Corp.) combina-tions are synergistic, working bet-ter than either alone, and becamethe standard in the industry short-ly before Marathon was market-ed. Several new products are indevelopment, so check occasional-ly with your regional extensionspecialist on the current status ofproducts for whitefly control.Attending regional or nationalgrower meetings and subscribingto extension or trade publicationsis helpful for keeping up-to-date.

AFTER BRACTFORMATION

Sometimes growers still findlate-season surprises, so we havelooked at a number of possible

alternatives to Plantfume andDithio for whitefly control dur-ing and after bract formation. Wehave also treated plants withmiticides that have been effectivein our trials against Lewis mite.Although these were fairly unsci-entific, we looked at a large num-ber of cultivars and made repeatapplications in “worst case” sce-narios. Treatments were usuallyapplied late in the day and atmaximum (or above) label rates. Ido not advise growers to try this.

In 1998, 41 poinsettia cultivars infull color were treated twice threedays apart with TriStar at 0.09 oz.per 100 gal. (this is much lowerthan the current high label rate offour packets or 2.3 oz.), Talstar (40oz.), Sanmite (Scotts Company) (4oz.) or Marathon 60W (the liquidformulation was not yet available).We also tried treating these sameplants with a space mix of theaerosols Attain TR (WhitmireMicro-Gen) + PT 1300 Orthene TR(Whitmire Micro-Gen) three timesat 2- to 3-day intervals at ratesexceeding normal label use.Duraplex TR (Whitmire Micro-Gen) was also released three timestwo days apart. For each spray,attention was given to full coverageand heavy deposition on bracts ç

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1300 Orthene TR Whitmire Micro-Gen

Astro FMC Corp.

Attain TR Whitmire Micro-Gen

Avid Syngenta Professional Products

Aza-Direct Gowan Company

Azatin XL Olympic Horticultural Products

Decathlon 20 WP Olympic Horticultural Products

Decree SePRO Corp.

Distance IGR Valent USA Corp.

Duraplex TR Whitmire Micro-Gen

Endeavor Syngenta Professional Products

Enstar II Wellmark International

Flagship Syngenta Professional Products

Floramite 50W Crompton/Uniroyal

Marathon Olympic Horticultural Products

Mavrik aquaflow Wellmark International

Ornazin SePRO Corp.

Orthene TTO 97 Valent USA Corp.

Sanmite 75 WP The Scotts Co.

Scimitar WP Syngenta Professional Products

Strike Olympic Horticultural Products

Talstar FMC Corp.

Tame 2.4 EC Valent USA Corp.

TriStar Cleary Chemical Corp.

Figure 1. Chemicals mentioned in this article available for control of whiteflies on poinsettia.

in particular. We saw no injury inany case, although residue wasvery noticeable following use ofTalstar or Sanmite. We will be look-ing at more realistic (higher) ratesof TriStar this year.

In 1999, we tried applyingFlagship 25WG (8 oz. per 100 gal.)or Endeavor (10 oz.) sprays twicefive days apart to 42 cultivars infull bract. Endeavor left noticeableresidue; note the label specificallyprohibits application to poinsettiabracts. There was no injury ineither case. Two years ago welooked at Endeavor again (5 oz.),and also at Avid (SyngentaProfessional Products) (8 oz., twicethe label rate for mites), Azatin XL(16 oz.) or Orthene TTO 97 (ValentUSA Corp.) (0.25 lb.) + Decathlon(1.9 oz.) sprays applied four times atweekly intervals during bract for-mation on ‘Freedom Red’ poinset-tias. There was again no injury withany of these, although Endeavorshowed a fair bit of residue espe-cially on darker colors.

Finally, we tried the same Avidand Orthene + Decathlon sprays,applied once to several varieties infull color, but this time we com-bined them with either Strike(Olympic Horticultural Products) (2oz.) for mildew or Decree (SePROCorp.) (24 oz.) for Botrytis as tankmixes (i.e., Avid + Strike, Avid +Decree, Orthene + Decathlon +Strike or Orthene + Decathlon +Decree). In no case did we seesymptoms of injury to flowers orbracts, although there was a notice-able brown residue on light-coloredbracts where Decree was used. Theresidue would be much less appar-ent if normal rates were applied asrecommended on the label. As aside note, we have also found thatrepeat applications of Floramite50W (Crompton/Uniroyal) at thehighest label rate (4 oz.) were notinjurious to a variety of cultivars.

Keep in mind these trials aredone for experimental purposes;growers should always follow labeldirections and restrictions. I stilladvise conducting small-scale testsin your own greenhouse under localconditions since there are so manyvariables from one operation to

another. However, our experiencesuggests several possible rescuetreatments to consider should awhitefly or mite problem arise atthe worst possible time. We plan tocontinue additional tests this winterwith some of the newer products, sostay tuned for future updates.

Daniel Gilrein is extension entomolo-gist at Cornell Cooperative Extensionof Suffolk County, N.Y. He can bereached by phone at (631) 727-3595or E-mail at dog1@cornell.edu.

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For more information about theproducts mentioned in this article,contact the following companies.

Cleary Chemical Corp.(800) 524-1662www.clearychemical.com

Crompton/Uniroyal(800) 243-3024www.cromptoncorp.com

FMC Corp. (215) 299-6000www.fmc.com

Gowan Company (800) 883-1844www.gowanco.com

Olympic Horticultural Products (800) 659-6745www.olympichort.com

SePRO Corp. (800) 419-7779www.sepro.com

Syngenta Professional Products (866) SYNGENTAwww.syngentaprofessionalproducts.com

The Scotts Co. (800) 492-8255www.scottsprohort.com

Valent USA Corp. (800) 898-2536 www.valent.com

Wellmark International(800) 877-6374www.wellmarkinternational.com

Whitmire Micro-Gen(800) 777-8570 www.wmmg.com