pests & diseases Whiteflies are not Flies But they can be a big problem. New research shows the best control methods. By James A. Bethke, Heather S. Costa and Richard A. Redak Above left: Adult silverleaf whitelfy; Right: Silverleaf whitefly nymphs. o, whiteflies are not flies. Flies like the typical housefly Figure 1. Mean number of live silverleaf whitefly nymphs on poinsettias treated with belong to the order Diptera, which has only two wings. selected insecticides one, four and six weeks after treatment. Whiteflies are in the order Homoptera and have four wings. The order Homoptera also include cicadas, plan- thoppers,N treehoppers, leafhoppers, sharpshooters, spittlebugs, psyl- lids, scale insects, mealybugs and aphids. There are over 1,200 species of whiteflies identified worldwide; how- ever, only a few of them are classified as pest species. Newly introduced species of whitefly can quickly become pests and may adapt to new host plants and environmental conditions. For example, one year after the silverleaf whitefly reached greenhouses in California, it replaced the greenhouse whitefly as the dominant species on poinsettias. MONITORING FOR WHITEFLIES Any whitefly management program will require the use of monitoring practices to be effective. Accurate records of pest numbers, crop damage and changes in whitefly num- bers will allow the develop- ment of treatment thresholds for specific crops and can help Jim Bethke will be part to time pesticide applications. of the GPN/Syngenta Yellow sticky cards are an Educational Symposium effective method for monitor- Recognizing hotspots and treating them early may reduce the overall need during 2002. You can ing adult whiteflies. One trap for pesticide applications. Because traps only capture winged adults, it is hear him speak about per 1,000 sq. ft. of growing area important to also monitor plants. For more information about monitoring, mode of action, chemical screening is recommended. Place traps a see page 108. and other insect-related topics at the few inches above the plant following venue: canopy, and move them up as PRODUCTION CONTROLS plants grow. Check the traps Since whitefly infestations can easily go unnoticed until they reach high Ornamentals Northwest Seminars weekly, and keep a good Portland, Ore. numbers, it is important to minimize potential infestations by employing all August 23 record of trap counts. possible control tactics prior to chemical control. Begin the cropping cycle www.farwestshow.com 58 GPN August 2002 pests & diseases Dramm Autofog sponsored by: • Automatic Aerosol Application INTEGRATED PEST MANAGEMENT • Creates Billions of Micro-particles for Even Coverage 800.258.0848 [email protected] • Perfect for Control of Whiteflies dramm.com Figure 2. Mean percent mortality of silverleaf whitefly All whitefly stages typically occupy the nymphs one, two, three and four weeks after treatment. undersides of leaves of infested plants. The more Poinsettias were treated with selected insecticides. susceptible stages are the younger nymphs. The Treatments were made directly to the soil as a drench or later stages, such as the fourth instar and redeye granular treatment. stage, are more difficult to control. Therefore, the best control is achieved when a maximum effort is made to contact the undersides of leaves with repeated spray applications (about every six days) targeting the earlier, susceptible stages for a period of about three weeks. Heavier infesta- tions may require more applications for a more extended period of time. An effort should be made to hold whitefly Silverleaf whitelfy nymphs. The nymph at the bottom left populations in check early in the cropping has been parasitized by Encarsia formosa. cycle. Contact insecticides, including soaps and oils, may be more effective early in the growth cycle when the foliage is less dense and contact PUTTING MOTHER with young nymphs is more likely. Later in the NATURE TO WORK cropping cycle, when dense foliage is present, with pest-free plants, and exclude the pest, if a systemically acting material may be more Biological control methods possible, with exclusion screens. Many weeds efficient in reaching the insects. By Stanton Gill are good hosts for whiteflies. Therefore it is important to keep the growing area clean and CHEMICAL CONTROLS ith restricted re-entry intervals, free of weeds. Biologicals are also a good control Figures 1-4, pages 58-62, are summaries of and fear of resistance devel- method for whiteflies; see the sidebar at the recent whitefly trials conducted at the right for information about biologicals. ➧ W opment, many growers are University of California-Riverside. Some of looking for alternative methods for controlling Table 1. Whitefly Control Methods. whiteflies, and some of them are turning toward biologicals. The most interesting new developments in biological control are with Pesticide Common name Chemical Class Manufacturer Trade Names natural enemies such as parasitoids, preda- Beauveria Biological Mycotech BotaniGard tors and pathogens, though there are also a pyrethrin/PBO botanical Whitmire MicroGen, PT 1100, number of oils, soaps and other biological Agrevo Pyrenone Crop Spray agents (see Table 1, left for a listing of con- Pyrethrin/Rotenone Botanical Webb Wright Pyrellin EC trols and manufacturers). Imidacloprid Chloronicotinyl Olympic Horticulture Marathon Azadiractin IGR Themo Trilogy Azatin XL PARASITOIDS S-kinoprene IGR Wellmark Enstar II Several species of whitefly parasitoids Diflubenzuron IGR Crompton/Uniroyal Adept occur naturally in the United States and Novaluron IGR Crompton/Uniroyal Pedestal may migrate into greenhouses and attack Pymetrozine Pyridine Syngenta Endeavor whiteflies. However, the degree of control Pyriproxifen Pyridine Valent, Distance, Pyrigro is usually insufficient. Augmentative releas- Whitmire MicroGen es of commercially reared parasitoids are Neem oil Oil Thermo Trilogy Triact 90 typically more effective. Horticultural oil Oil Whitmire MicroGen Ultra-Fine Oil Parasitoids that have been used success- Endosulfan * Organochlorine Gowan Endosulfan fully in greenhouse crops include tiny wasps of Chlorpyrifos/Cyfluthrin Organophos./pyreth. Whitmire MicroGen PT Duraplex TR several Encarsia and Eretmocerus species. Acephate Organophosphate Valent, Orthene, PT 1300 These wasps attack whitefly nymphs, killing Whitmire MicroGen them in one of two ways. First, the female Sulfotep * Organophosphate Plant Products Inc. Plantfume 103 wasp uses her needle-like ovipositor to lay an Diazinon Organophosphate Cleary KnoxOut egg within or beneath a whitefly nymph. Dimethoate Organophosphate various various Encarsia sp. prefers the third to fourth instar Malathion Organophosphate various various whiteflies. The egg hatches, and the parasitoid Bifenthrin * Pyrethroid Whitmire MicroGen Talstar maggot feeds on the nymph. Pupation occurs Cyfluthrin Pyrethroid Olympic Horticulture Decathlon within the nymph. When the adult wasp Fenpropathrin * Pyrethroid Valent Tame emerges from the whitefly pupa, it chews a round exit hole through the cuticle at one end Fluvalinate Pyrethroid Wellmark Mavrik Aquaflow of the whitefly pupa. Second, the female wasp Permethrin Pyrethroid FMC Astro punctures the whitefly nymph with her oviposi- Pyridaben Pyridazinone BASF Sanmite tor, killing the nymph, and feeds from the fluids Soap Soap Micro-Flo, Insecticidal Soap Olympic Hort. that exude from the wound. The wasps do not attack adult whiteflies. ➧ * Restricted use material. August 2002 GPN 59 pests & diseases the pesticides are registered for cide applicator’s responsibility to tion (see Table 1, page 59). In Encarsia formosa is a very use on the intended target; others follow all label directions. No addition to Marathon (imidaclo- tiny wasp (0.6 mm), with a are experimental. We do not endorsement is intended for prid), several new chloronicoti- black head and thora, a pale always use labeled rates in our products mentioned, nor is criti- noids like acetamiprid (Aventis), yellow abdomen and transpar- trials because these trials are for cism meant for products mistak- Forte (a new formulation of imi- ent wings. Females give rise to experimental purposes — to enly omitted. dacloprid, Bayer), thiamethoxam females; males are rare. increase our knowledge about There are a relatively large (Syngenta) and thiacloprid Greenhouse whitefly pupae the products and their capabili- number of insecticides available (Bayer), have been registered that have been parasitized by ties. Labels constantly change; for chemical control of whiteflies, recently or are in the development Encarsia formosa turn black; therefore, it is always the pesti- providing many options for rota- phase. All of these materials are silverleaf whitefly pupae turn very effective against whiteflies. amber-brown. The adult wasps Figure 3. Mean number of emerged adult silverleaf whiteflies from treated poinsettias three In addition, a new Novaluron are rarely noticed and should weeks after treatment. from Crompton/Uniroyal not be a deterrent in sale of the (Pedestal) looks very promising plants. This parasitoid is widely (see Figures 3-4, pages 60-62). used for biological control of Whiteflies typically have sev- greenhouse whitefly on green- eral generations each year, espe- house vegetables. Release cially in a greenhouse environ- rates vary from 3-6 wasps per ment. They take about 21-25 square foot of growing area days to develop to an adult, with repeated releases at 7- to depending on temperature. 14-day intervals. Encarsia will Because the nymphs are on