AFE Research Reports
p class=MsoNormal>Since 1961, the American Floral Endowment (AFE) has invested$11 million in scientific research and educational programs. The SpecialReports are a result of Endowment-funded scientific research projects atuniversities throughout the United States. The reports are written by some ofthe industry’s most respected researchers and are set up to provide readerswith a basic understanding of the projects, the results and how results canimprove horticulture. They are intended to assist in the production ofhigh-quality plants and flowers, improve the care and handling of flowers, andhelp increase profitability.
The Special Reports are part of the Endowment’s SpecialReport Notebook Program, a project started several years ago to disseminate keyscientific and educational research. Each year, donors receive new Special Reports,annual progress reports and, if available, consumer marketing articles. Thisinformation is inserted in a special three-ring binder called the SpecialReport Notebook and is an important reference tool. Special Report Notebooksmay be obtained by making a contribution to AFE. Contributions to the Endowmentare tax deductible as allowed by law and support the funding of scientificresearch for new knowledge and technology, fund educational programs to attracttalented people to the floral industry, and support the only industry-basedstatistical/marketing research and data collection program.
The following are three Special Reports from the 2003Notebook.
Effective Release of Natural Enemies
By Kevin Heinz, Texas A&MUniversity
Biological control has been proposed as a method forcontrolling insect pests of floricultural crops for many years. Althougheffective across many pest-crop systems, the 3-10 fold increase in the monetarycosts typically associated with biological control prevents some growers fromembracing it as a regular practice.
Currently, approximately 50 species of parasitoids,predators and pathogens are available from commercial insectaries for use tocontrol arthropod pests of greenhouse and nursery crops. Two questions arecentral to their efficient and economical use. When should biological controlbe initiated, and how should natural enemies be optimally released to maximizetheir efficacy? Answers to these questions are needed not only to makebiological controls effective in the specific systems utilized but also for thegeneral practice of biological control in greenhouse and nursery crops.
When To Release For Mites
In a commercial greenhouse, plants infested with two-spottedspider mites (Tetranychus urticae) were arranged into three groups based ontheir planting date. Within each age group, plants were allocated to one of twotreatment groups: biological control or grower derived chemical controlprogram. Each age-by-treatment group was replicated four times. TwoPhytoseiulus persimilis were released weekly per pot for the biological controltreatments, while the grower applied insecticides as perceived in the chemicalcontrol treatments. In all three treatments (recently potted plants, plants inmid production and plants near harvest), releases of P. persimilis providedbiological control of T. urticae. However, plants in mid-production and nearharvest harbored moderate to high densities of mites prior to achievingsuccessful biological control. Thus they had significant crop damage. Incontrast, releases initiated at the beginning of the crop cycle yieldeddamage-free plants. Also, insect control was significantly greater than thechemical control program.
Cost for the biological control program was almost 10percent less, and the level of control was greater than the weekly sprayprogram used by the grower. Southwest greenhouse growers are now using regularreleases of P. persimilis to control mite problems on foliage plants andminiature roses.
How To Release For Aphids
Aphids are serious pests of floricultural crops worldwide.Because outbreaks can occur rapidly, aphid control requires that sufficientnumbers of natural enemies be released and that natural enemies rapidly locatepatches of infestation.
Greenhouse studies documented the ability of green peachaphids to spread over an area of 120 sq.ft. per day after infesting a singlepotted chrysanthemum. Natural enemies must be capable of spreading at leastthis rapidly to prevent local infestations from becoming problematic.
In greenhouse studies, green lacewing larvae, used as modelpredators, were incapable of navigating among potted chrysanthemums placed onsolid benches. Although lacewing larvae voraciously consume aphids oncediscovered, successful biological control requires placement of lacewing larvaeonto each individual plant infested with aphids.
By comparison, studies with the parasitoid wasp A. colemanidemonstrated that it could spread over an area of 147 sq.ft. per day. Fromthese results, we determined that the most effective biological aphid controlcould be obtained by releasing A. colemani from points no greater than 12 feetapart within a potted chrysanthemum greenhouse.
The release technology developed was evaluated in commercialchrysanthemum greenhouses in terms of pest control, economic feasibility andgrower acceptance. The effectiveness of natural enemy releases was determinedby comparing aphid populations in grower-treated ranges with aphid populationsin experimental ranges receiving natural enemy releases using a haphazardrelease method or an optimal distance. Each treatment was replicated threetimes. Natural enemies were released weekly into each of the ranges at a rateof one wasp per plant.
Use of the optimal release distances (4x) resulted in significantlygreater aphid biological control than the haphazard method (1x) and incomparison to plots not receiving any wasps. Use of the optimal release ratecost the grower 1.2-1.3 times the cost of insecticide applications. Incontrast, haphazard releases cost the grower 2-3 times the cost of insecticideapplications. The quality of plants harvested from the optimal release distancewere equivalent to those harvested from the insecticide check plots andsignificantly greater than plants harvested from the haphazard and no releaseplots.
Adaptation of this approach to other biological controlprograms should improve efficacy and reduce costs.
Managing Thrips and Whiteflies with Fungi
By Michael Brownbridge,Margaret Skinner and Bruce Parker, University of Vermont
Methods of plant protection are undergoing major changes asmany of the “standard” pesticides are withdrawn from the market.Insect-killing fungi are an important new weapon in the IPM arsenal, butinformation describing their effective use is needed. In these studies, wetested two “off-the-shelf” sprayers for application of the fungusBeauveria bassiana for control of western flower thrips on chrysanthemum andsilverleaf whitefly on poinsettia.
MATERIALS AND METHODS
Spray equipment. The sprayers tested were a high-volumehydraulic sprayer (Dramm Corp.) and an electrostatic sprayer (ESS).
Application. Plantswere artificially infested with thrips or whiteflies and sprayed withBotaniGard WP at the recommended rate.
Chrysanthemums.Plants were sprayed every five days (total four treatments) using a standardspray gun at 200 psi or the ESS sprayer. Efficacy was evaluated by samplingthrips from flowers.
Poinsettia. Plantswere sprayed using a five-nozzle extension lance, spraying up into the leaf canopy.Four sprays were applied at seven-day intervals. Whitefly populations weresampled every seven days. Spore deposition and persistence were determinedusing a leaf press technique.
RESULTS
Chrysanthemums were in flower at the start of the trial, a timewhen thrips populations can dramatically increase. Even so, compared to theuntreated “checks,” both sprayers suppressed the increase in thrippopulation. The high-volume spray provided better levels of control (See Figure1, page 20), but high levels of thrips infection were obtained with bothsprayers (See Figure 2, page 20).
Interestingly, infected thrips were also recovered from theuntreated check plants, indicating movement of infected insects from sprayed tonon-sprayed areas. This natural “spread” may be an important benefitwhen using fungi in a control program. Á
On poinsettia, high-volume sprays successfully suppressedthe whitefly population (See Figure 3, below). Greater efficacy may haveresulted from better targeting of spores to the underside of the lower leaveswhere the highest whitefly populations are found. Spore counts taken directlyfrom the leaf surface confirmed this. Spores remained viable throughout thespray process and remained viable on the leaves for less than six days.
CONCLUSIONS
Under grower conditions, control measures would be appliedbefore pest populations reached the levels used in these trials. Thus, fungiare best used as preventatives. Increased levels of thrip and whitefly controlwere obtained with the hydraulic sprayer, probably because of better targetingof the pests. Also, the higher spray volume may have provided better leafcoverage and movement of the spores to infestation sites in flowers andinfection sites on the insects.
IMPACT TO THE INDUSTRY
(1) Plants must be scouted regularly so that fungal sprayscan be initiated before pest populations reach outbreak levels.
(2) Growers can use fungi within an IPM strategy to regulatethrips and whiteflies. Their unique mode of action makes them ideal for use inresistance management.
(3) Targeted spray applications using a high-volume sprayerappear to provide the best levels of control.
(4) When fungi are used within an IPM program, pesticideresidues on plants handled by retailers and wholesalers will be significantlyreduced.
Management of a New Powdery Mildew on Poinsettia
By M. Daughtrey, CornellUniversity, and J.M. Byrne and M.K. Hausbeck, Michigan State University
In 1988, a new powdery mildew first appeared on poinsettiacrops in North America. Few powdery mildew fungicides were labeled for use onpoinsettia, and the biology of the fungus, an Oidium species, was relativelyunknown. Research was initiated to obtain information critical for diseasemanagement.
MATERIALS AND METHODS
Fungicides. Sixteenpreventive fungicide treatments were compared on poinsettia ‘Freedom Red’.Powdery mildew inoculum was introduced 48 hours after the first fungicidetreatment on October 14. Colonies were counted weekly on four previouslyselected leaves and bracts of each plant.
Infection was studied in relative humidity (RH) chambersproviding 35-92 percent RH at 59, 68 and 77° F. Inoculated leaf disks wereincubated for 48 hours, stained with “cotton blue” and examinedmicroscopically.
Spore production.The effect of temperature on spore production was measured using leaf disksheld on agar disks in petri dishes for 14 days at 59 or 68° F. Sporenumbers and chain length were counted microscopically.
Symptoms of infection.Symptoms of powdery mildew are often latent until fall, when greenhousetemperatures become lower than 86° F. Colonies on leaf undersurfaces may behard to detect. Careful scouting and early detection are essential for precisemanagement of powdery mildew on poinsettias.
CONCLUSIONS
Greenhouse Control Study. Untreated controls developed 12 colonies per leaf and 22 colonies perbract by December 10. No powdery mildew was observed on plants treated every 14days with sterol biosynthesis inhibitors Systhane 40WP, Terraguard 50WP andStrike 25TOF or with Pipron 84.4 EC or Nutrol applied every seven days (appliedwith Latron B-1956 spreader-sticker). Excellent suppression was also obtainedwith 3336F + Latron B-1956, Phyton 27 21.8EC, Milsana 114UBF/FL and ZeroTol 27percent applied every seven days and with Cygnus 50WDG, Compass 50WG andHeritage 50WG applied every 14 days.
Most treatments were free from phytotoxicity, but some bractspotting was observed with ZeroTol and Milsana. Residue was moderate to heavyin 3336F, Milsana and Nutrol treatments. Residue in treatments with 3336F usedalone was reduced by alternating treatments of 3336F and First Step.
Microscopy Studies
Environmental effects on infection
Environmental effects on sporulation
IMPACT TO INDUSTRY
(1) Knowing the effects of temperature on this powderymildew allows growers to manipulate environmental conditions to slow thedevelopment of an epidemic. Less inoculum will be produced if temperatures are temporarilylowered from 68-59° F. This allows environmental control to be used as onecomponent of an IPM program that also uses scouting and appropriate fungicides.
(2) Growers may utilize the appropriately registeredfungicides found to be effective in this control trial to significantly reducedisease. Growers can choose materials with demonstrated low residue and minimalchance of phytotoxicity. In order to reduce fungicide residue, growers may beable to use the strategy of alternating a high-residue material with abicarbonate.
(3) Retailers and wholesalers have a reduced risk ofpurchasing poinsettias with powdery mildew. Because it thrives at moderatehumidities, this particular powdery mildew may become much more visible duringretail or in churches, homes or lobbies. Thus, careful management in greenhouseproduction is critical for retail performance.
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