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GREENHOUSE WHITEFLY MANAGEMENT PAGE 4 PRODUCTION GUIDELINES Commission 01-06, Watsonville, CA

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GREENHOUSE WHITEFLY MANAGEMENT PAGE 4 PRODUCTION GUIDELINES Commission 01-06, Watsonville, CA PRODUCTION GUIDELINES: GREENHOUSE WHITEFLY MANAGEMENT PAGE 4 PRODUCTION GUIDELINES Commission 01-06, Watsonville, CA. GREENHOUSE WHITEFLY MANAGEMENT Bi, J. L., N. C. Toscano, and G. R. Ballmer. 2001. Seasonal population dynamics of the greenhouse whitefly Trialeurodes vaporariorum in Oxnard area. The Pink Sheet, California Strawberry Commission NICK TOSCANO, FRANK ZALOM & JIAN BI 01-12, Watsonville, CA. Issue 2 February 2007 Bi, J. L., N. C. Toscano, and G. R. Ballmer. 2002a. Greenhouse and field evaluation of six novel insecti- cides against the greenhouse whitefly Trialeurodes vaporariorum on strawberries. Crop Prot. 21:49-55. Greenhouse Whitefly Management The greenhouse whitefly, Trialeurodes vaporariorum, is an important pest of Bi, J. L., N. C. Toscano, and G. R. Ballmer. 2002b. Field evaluations of novel chloronicotinyls and novel strawberries in the coastal areas of insect growth regulators against the greenhouse whitefly on strawberry. HortScience. 37:914-918. California. The greatest problem with greenhouse whiteflies occurs in the Contact Information Oxnard/Ventura area, but damaging den- Nick Toscano Frank Zalom Jian Bi sities of this pest can be found elsewhere Department of Entomology Department of Entomology Dept. of Entomology in southern California and in the University of California, Riverside University of California, Davis University of California, Riverside Watsonville/Salinas area. E-mail: [email protected] E-mail: [email protected] E-Mail: [email protected] Ph: 951.827.5826 Ph: 530.752.3687 Ph: 951.827.3725 Identification Whitefly adults are about 1/10 inch in length, with four membranous wings that are coated with white powdery wax. The eggs are elongated, vary in color from a pale yellowish green to brown, smooth elongated and attached to the leaf surface by a short pedicel. They turn black before Figure 1. Greenhouse whitefly eggs that are black, indicating they are hatching (figure 1). The immatures do not about to hatch. look like the adults, and do not have wings or antennae. They are oval, thin, flat and often semitransparent. February 2007 Toscano, Zalom & Bi February 2007 Toscano, Greenhouse whitefly pupae can be recog- nized by the long waxy filaments attached to their bodies. Adult greenhouse white- flies are white and hold their wings flat over their backs (figure 2). Life history and damage Whiteflies go through six stages in their development: eggs, first, second, third, and fourth instar nymphs, and the adult (figure 3). Whiteflies do not have a true pupal stage, but the last stage of the fourth instar when the red eyes of the adult whitefly begin to appear is often referred to as the pupal stage. Only the Figure 2. Greenhouse whitefly adult and ‘pupae’. adults and the newly hatched first instar nymphs are mobile. Development from egg to adult may take as little as 18 days depending upon temperatures and host plant. Whiteflies pre- fer warmer temperatures and develop fastest when temperatures are between 80o and 90o F. Crawlers are the first instar nymphs that hatch out of the eggs. The crawlers disperse on the host plant until they are successful in probing sap with their mouthparts from the plant’s phloem tissue. Once they find a suitable feeding site, they remain immobile until becoming adults. Adult whiteflies force open a T-shaped slit as they emerge from the shell of the fourth instar. It may take several hours after emergence for the whitefly’s wings to dry and they are able to fly. Adult whiteflies CALIFORNIA STRAWBERRY COMMISSION P.O. BOX 269 WATSONVILLE, CA 95077 PH: 831.721.1301 FAX: 831.724.5973 WWW.CALSTRAWBERRY.COM also feed on the plant. © 2007 CALIFORNIA STRAWBERRY COMMISSION PRODUCTION GUIDELINES: GREENHOUSE WHITEFLY MANAGEMENT PAGE 2PRODUCTION GUIDELINES: GREENHOUSE WHITEFLY MANAGEMENT PAGE 3 Whiteflies breed and develop continually for the various whitefly stages. All stages of whiteflies can be found on the underside of the trifoliates, as long as temperatures are warm. Adult therefore when inspecting leaves for whiteflies the leaves should be turned over and the whiteflies female whiteflies may mate and start lay- noted. Research has shown that 10-20 whiteflies per leaf can reduce the soluble sugars in the plant ing eggs within a day of emergence from and therefore cause a reduction of sugar to the berry, and strawberry yield decreased as whitefly-days the fourth instar stage. Whiteflies make (a measure of cumulative whiteflies per leaf) increased over time. In a field study in Watsonville, an relatively short flights from plant to plant adult whitefly population of 10 per leaf in March reduced yield on fall planted strawberries by 10 per- or field to field, but they are capable of fly- cent, and an adult whitefly population of 50 per leaf reduced yield by almost 25 percent. ing two or more hours. Whiteflies may be carried a great distance by wind or on Cultural control host plants. The best way of controlling whiteflies is a combination of crop clean up and insecticides. The continu- ous development cycle of whiteflies must be broken by eliminating infested hosts for some period of the Host plants year. This can be achieved by controlling infestations on alternate crops, removing older infested crops, The greenhouse whitefly has a large host and controlling infestations on second year strawberries or summer plantings through physical means range and can be destructive to many or by applying insecticides. An area wide approach may be needed to reduce whitefly populations caus- plants in California. Among its many hosts ing damage to crops and invading urban areas when whitefly infestations become widespread. This are alfalfa, avocados, beans, begonias, approach has been necessary in Ventura County where area wide management should be initiated blackberries, chrysanthemums, citrus, before May each year. clover, cucumbers, eggplants, geraniums, Figure 3. Greenhouse whitefly life cycle. grapes, hibiscus, honey locust, black Biological control locust, lantana, lettuce, loganberries, Natural enemies of the greenhouse whitefly include big-eyed bugs, minute pirate bugs, lacewing larvae lupine, Indian mallow, malva, morning and several native parasitic wasps including Encarsia pergandiella. Although augmentative parasite glory, melons, nightshade, oxalis, peas, releases have been used successfully in greenhouses, releases of commercially available species such peppers, potatoes, primrose, roses, rasp- as Encarsia formosa and Eretmocerus eremicus have not been used successfully in California straw- berries, strawberries, tomatoes, and berries where the greenhouse whitefly has been a problem. vetch. Insecticides Damage Greenhouse whitefly nymphs and eggs are generally laid on the underside of the trifoliates in the mid- Whiteflies can damage strawberry plants dle of the strawberry plant and the nymphs are covered with wax. This makes contact by insecticide in several ways. They can reduce yield sprays difficult. Therefore, adult whiteflies are often easier to control than the more damaging nymphs directly through their feeding on leaf tis- with most of the traditional insecticides presently registered for use on strawberries. A few materials are sue, which removes plant sap and stunts effective against nymphs and eggs. It is important to know how a specific insecticide works, and then plant growth or producing sticky honey- deliver the insecticide at the timing and the manner that will provide the best control possible. dew they excrete during feeding, reducing Imidacloprid (Admire Pro® or Alias®), a systemic neonicotinoid insecticide, can provide up to 11 weeks the market value of berries and other control when applied at planting or preplant at the full label recommended rate. Imidacloprid has to get crops (figure 4). The honeydew may cover into the plant to be effective. In strawberries, this is best done by the injecting the insecticide into the plants and support the fungus that causes planting hole, or if applied by drip irrigation by watering thoroughly to insure that the chemical gets to black sooty mold. Greenhouse whitefly the root zone. A pre and post irrigation after applying imidacloprid is recommended. Pyriproxyfen can transmit plant viruses including straw- Figure 4. Greenhouse whitefly damage-strawberry plant covered with (Esteem) is an insect growth regulator which mimics the whitefly’s juvenile hormone, resulting in sup- berry Pallidoses associated virus and black sooty mold. pression of egg development and adult formation. Because of pyriproxyfen’s mode of action suppres- Beet Pseudo Yellow virus which can sion of whitefly numbers may not be realized until 3-4 weeks after application. Pyriproxyfen is very cause a rapid plant decline in strawberry when they are present with other viruses. effective in reducing whitefly populations for up to 7 weeks. Spiromesifen (Oberon) is an insecticide that interferes with insect/mite lipid biosynthesis. Spiromesifen is especially active against the greenhouse Monitoring and Management whitefly, it inhibits egg hatching and is very effective against first, second and third instar nymphs. Two monitoring methods, yellow sticky traps and/or leaf counts, can be used together in a comprehen- Some toxicity to adult whiteflies also occurs when this insecticide is applied to strawberries. Methomyl sive monitoring program to detect whiteflies, to determine the need for timing of treatments and to eval- (Lannate) and tank mix of fenpropathrin (Danitol) + malathion will provide control of whitefly adults and uate control. Yellow sticky traps catch adults as they move into strawberry fields. Place one sticky trap early instar nymphs post planting, but these materials have a very short residual of only 3-7 days. every ten acres next to the edge of the strawberry field. Place yellow sticky cards vertically on stakes, just above the crop canopy. Count whiteflies weekly, being sure to distinguish them from other small fly- References ing insects that may get stuck on the traps. Sticky traps are useful for detecting whitefly infestations and Bi, J. L., G. R. Ballmer, and N. C. Toscano. 2000. Field evaluation of various insecticides against the determining relative infestation levels.
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