Greenhouse IPM: Sustainable Whitefly Control
Pest Management Technical Note
NCAT Agriculture Specialist
© NCAT 2000
This publication focuses on integrated pest management for greenhouse whitefly on both vegetable and ornamental crops. It is designed to complement the ATTRA publication Integrated Pest Management for Greenhouse Crops, which discusses techniques for good greenhouse supervision. Monitoring of whiteflies, biological controls, biopesticides, and insect growth regulators are discussed below. The appendices include information on the newest biopesticides and biological control organisms.
Table of Contents
- Crop Scouting and Trapping
- Biological Control
- Biorational Pesticides
- Insect Growth Regulators
- Controlled Atmosphere
- Web Sites
- Appendix 1: Beneficial Organisms
- Appendix 2: Biorational Pesticides
Whiteflies began showing resistance to synthetic insecticides early on, and by the 1980s they were a very serious greenhouse pest. Not only do they feed on plants, but they also produce honeydew, which detracts from the plants' appearance and attracts other insects and sooty mold. Whiteflies can also transmit plant viruses. The mere presence of whiteflies in a greenhouse will stop customers from buying your product.
Several species of whiteflies attack greenhouse plants, and they typically have a wide host range and resist insecticides. Greenhouse tomatoes and poinsettias are especially plagued by whiteflies. The most common whiteflies on greenhouse crops are the greenhouse whitefly (Trialeurodes vaporariorum), sweetpotato whitefly (Bemisia tabaci) and the silverleaf whitefly (Bemisia argentifolii).
The various whitefly species and biotypes look very much alike, but they have subtle physiological differences. These differences can cause them to respond differently to control strategies. Because control measures must be selected according to the type of whitefly present, accurate identification is critical to successful control. The Cooperative Extension Service is an excellent resource for assistance with pest identification. There are also several Web sites that provide pictures of the various whiteflies. See the Web Sites section for more information.
Crop Scouting and Trapping
Plants should be visually inspected for signs of a whitefly infestation—e.g., off-color or stunted plants. A hand lens is useful for systematically inspecting a number of individual plants for the presence of eggs, nymphs or adults. Both the upper and lower leaf surfaces should be inspected. It is important to check the greenhouse in the same pattern on each scouting trip. Locations where whiteflies are found should be flagged so that population development and control efforts can be evaluated. Scouting frequency should be increased during warm weather as whitefly populations multiply faster then.
Trapping with yellow sticky cards, both inside and outside the greenhouse, is essential for a successful whitefly management program. The cards are used to detect and monitor population levels. As a general rule, 1 to 4 cards spaced evenly throughout 1000 square feet of greenhouse are sufficient. (1) A generally acceptable threshold for whiteflies is 0.5 per card per day when the crop is young, and 2 per card per day as the crop reaches maturity. (2) Traps should be hung level with the tops of the plants since whiteflies are most attracted to young foliage. Doors, vents and other openings where whiteflies can enter the greenhouse are other good sites to hang yellow sticky cards.
Researchers in California have successfully used silver-painted pot spaces and silver polyethylene mulch to control whiteflies on greenhouse poinsettias. (3) The reflective materials were used in conjunction with yellow sticky cards or tape and resulted in significantly enhanced trapping of whiteflies, relative to controls with sticky traps only.
Greenhouse plastics themselves may have significant influence on the initial attraction of insects into greenhouses. A study from the late 1990s showed that silverleaf whiteflies preferred to enter greenhouses covered with film that transmitted higher levels of ultraviolet light. (4)
Several types of beneficial organisms are available for biological control of whiteflies. The parasitic wasp Encarsia formosa preys on immature whiteflies and is commonly used for greenhouse whitefly. Encarsia wasps kill whitefly nymphs in one of two ways: they either lay an egg inside the nymph, providing food for their young, or they kill the nymph right away and feed on the fluids inside of it. (2) Greenhouse whitefly pupae that have been parasitized by Encarsia formosa turn black; silverleaf whitefly pupae turn amber-brown. (2) The cost of E. formosa is comparable to foliar pesticides. (2)
Sweetpotato and silverleaf whiteflies are not well controlled by Encarsia formosa. Two other wasp parasites, Encarsia luteola and Eretmocerus californicus are commercially available for control of these species, but E. formosa remains the mainstay of most whitefly biological control programs due to the expense and intermittent availability of these other beneficials. (5) Researchers are also examining different strains of E. formosa to determine their effectiveness against sweetpotato and silverleaf whiteflies.
Mark Hoddle, University of California, Riverside, has done some recent research dealing with Eretmocerus eremicus. E. eremicus was effective for silverleaf whitefly control and is best used in combination with the insect growth regulators Precision™ or Applaud™. Enstar™ was not compatible with natural enemies he tested. Biological control should be used only at low whitefly levels (less than one nymph per 10 cuttings) and must be regularly evaluated. (6)
Mark has also compared the effectiveness of Encarsia formosa and Eretmocerus californicus on silverleaf whitefly. In a 1996 study, both parasitoids controlled whiteflies at a 99% control rate. However, fewer numbers of E. californicus had to be released, which would result in cost savings for growers. Another benefit: Fewer parasitoids meant more food for each, so the reproduction rate was much higher. (7)
Delphastus pusillus, sometimes called the whitefly destroyer, is a very small, black ladybird beetle that attacks all stages of whiteflies, but prefers eggs and nymphs. The females lay their eggs within clusters of whitefly eggs. Adults can consume 160 eggs or 12 large nymphs every day. A larva consumes 1000 whitefly eggs during its development. These beetles perform best at temperatures between 65 and 90°F, with relative humidity above 70%. These predators can be used in combination with Encarsia species. (8)
See Appendix 1 for a complete listing of biological controls for whiteflies.
Some microorganisms also control whiteflies. For instance, the fungus Beauveria bassiana (trade names Naturalis-O™ and BotaniGard™), is effective against eggs, immature and adult whiteflies. Thorough coverage of leaf undersides and correct timing of applications result in best control.
Another fungus, Paecilomyces fumosoroseus (trade name PFR-97™), is now commercially available. It controls whiteflies, aphids, and spider mites. Both B. bassiana and P. fumosoroseus need high humidity for best results.
Several least-toxic, or biorational, pesticides have been evaluated for their effectiveness against the different whitefly species. These include neem-based formulations (Neemazad™ and Azatin™ are two registered products), insecticidal soap (M-Pede™), and horticultural oil. Enhanced whitefly control is achieved with thorough spray coverage. Wider plant spacing and removal of dead lower leaves improve pesticide coverage and pest control.
A 1995 study conducted in Florida compared the effectiveness of Sunspray Ultra-Fine Spray Oil™, M-Pede insecticidal soap, a sucrose ester extract surfactant derived from tobacco, and Garlic Barrier™, for killing and repelling silverleaf whiteflies (Bemisia argentifolii) on tomatoes. Sunspray provided the best control, followed by M-Pede and the tobacco surfactant. The Garlic Barrier did not provide any control. (9)
Researchers at Ohio State University showed that mortality rates of silverleaf whitefly were higher when BotaniGard was used together with Adept™ (an insect growth regulator), insecticidal soaps, horticultural oil, Fulex SO-2000, glycerol and a yeast extract. (10) In most cases, the rate of infection and kill was faster than with BotaniGard alone. This is important because it would allow more biopesticides and biorationals to be used retroactively. When several substances are used together, they are applied at lower-than-recommended rates (one-tenth to one-half were used in this study). The researchers are trying to "develop management guidelines on spray-tank mixes that would enhance fungal efficacy." (10)
See Appendix 2 for a complete listing of biopesticides and biorational pesticides available for whitefly management.
Insect Growth Regulators
Insect growth regulators (IGRs) are another least-toxic pesticide control option. IGRs typically kill insects by disrupting their development. They have a complex mode of action that precludes insects from rapidly developing resistance. IGRs can work in one of several ways: 1) they can mimic juvenile hormones, so that insects never enter the reproductive stage of development; 2) they can interfere with the production of chitin, which makes up the shell of most insects; or 3) they can interfere with the molting process.
|Table 1. Selected Insect Growth Regulators|
|Adept, Dimlin, Azatin||Uniroyal Chemicals, Hydro-Gardens, Olympic Horticultural Products|
|Enstar II||Wellmark Int'l|
|Neemazad, Neemix||Thermo Trilogy|
|Preclude, Pyrigro||Whitmire Micro-Gen|
IGRs usually work through ingestion, so good spray coverage is essential. They generally don't affect non-target species-such as humans, birds, fish or other vertebrates. For most IGRs there are minimal re-entry restrictions. IGRs typically take several days to have an effect on pest populations. Because IGRs do not affect mature insects, adult beneficials released into the greenhouse after an IGR application are not likely to be affected. Use of IGRs is generally prohibited by organic certification organizations because the products are synthetic.
IGRs can sometimes be used in conjunction with biological control efforts and may provide growers with a "safety net" should beneficials fail to keep the pests below economically damaging levels. The table above lists some well-known insect growth regulators.
(See the Suppliers section for suppliers' contact information.)
Changing the composition of the atmosphere in the greenhouse by either reducing oxygen or increasing carbon dioxide appears to provide some control of greenhouse whiteflies, especially adults. Reduced-oxygen experiments by Dr. Susan Han at the University of Massachusetts resulted in 100% adult mortality after less than two hours of exposure, though eight-hour treatments were needed to control most (about 80%) of the eggs and pupae. (11)
Horticulturists at North Carolina State University reported that whitefly population levels were lower in greenhouses where carbon dioxide enrichment occurred daily for about eight hours. The likely reason for the population reductions is that plants grown in atmospheres with high carbon dioxide levels tend to have higher concentrations of carbohydrates in the plant tissue relative to nitrogen, resulting in a nitrogen-dilute diet for the whiteflies. Lower dietary nitrogen would slow the growth and reproduction of the pests, without adversely affecting crop yields or quality. (12)
Price, Robert P. Jr. 1999. Reflective mulches and yellow sticky tape control whiteflies in greenhouse poinsettia (Euphorbia pulcherrima). As reported in Williams, Greg and Pat. From the 1999 ASHS conference. HortIdeas. August. p. 85.
Costa, H.S. and K.L. Robb. 1999. Effects of ultraviolet-absorbing greenhouse plastic films on flight behavior of Bemisia argentifolii (Homoptera: Aleyrodidae) and Frankliniella occidentalis (Thysanoptera: Thripidae). Journal of Economic Entomology.
June. p. 557-562.
- Tripp, Kim and Mary Peet. 1993. New use for CO2: Slowing whiteflies. American Vegetable Grower. November. p. 43-44
|A-1 Unique Insect Control
5504 Sperry Drive
Citrus Heights, CA 95621
|Mycogen Crop Protection
5501 Oberlin Dr.
San Diego, CA 92121
P.O. Box 4247 CRB
Tucson, AZ 85738
P.O. Box 4109
Butte, MT 59702-4109
14751 Oak Run Rd.
Oak Run, CA 96069
|Natural Pest Controls
8864 Little Creek Dr.
Orangeville, CA 95662
P.O. Box 177
Willow Hill, PA 17271
P.O. Box 35
Medford, OR 97501
|Caltec Agri-Marketing Services
P.O. Box 576155
Modesto, CA 95357
|Novartis Crop Protection, Inc.
P.O. Box 18300
Greensboro, NC 27419-8300
|Florikan ESA Corp.
1523 Edger Place
Sarasota, FL 34240
|Olympic Horticultural Products
P.O. Box 1885
Bradenton, FL 34206-1885
|The Green Spot, Ltd.
93 Priest Rd.
Nottingham, NH 03290-6204
603-942-5027 (voice mail)
|Plant Health Care
440 William Pitt Way
Pittsburg, PA 15238
|Harmony Farm Supply
3244 Hwy. 116 No. F
Sebastopol, CA 95472
|Rincon-Vitova Insectaries, Inc.
P.O. Box 1555
Ventura, CA 93002
|Hot Pepper Wax, Inc.
305 Third St.
Greenville, PA 16125
11550 N. Meridian St., Suite 180
Carmel, IN 46032-4562
P.O. Box 25845
Colorado Springs, CO 80932
|Soil Technologies Corp.
2103 185th St.
Fairfield, IA 52556
|International Technology Services Inc.
P.O. Box 19227
Boulder, CO 80308-2227
|Stoller Enterprises, Inc.
8582 Katy Freeway, Suite 200
Houston, TX 77024
P.O. Box 300
Locke, NY 13092-0099
1000 Tower Lane, Suite 245
Bensonville, IL 60106
|M&R Durango, Inc.
P.O. Box 886
Bayfield, CO 81122
3568 Tree Court Ind. Blvd.
St. Louis, MO 63122
Appendix 1: Beneficial Organisms
|Chrysopa carnea (predator)||Natural Pest Controls, Beneficial Insectary, Caltec, Arbico, A-1 Unique Insect Control, Praxis, Rincon-Vitova, Hydro-Gardens||aphids, caterpillars, mealybugs, scales, spider mites, thrips, whiteflies||1 lacewing/5-30 aphids; 1000 eggs/200 sq. ft. Apply every 1-3 weeks as needed. May arrive as eggs, immatures, or adults.|
|Chrysoperla rufilabris (predator)||Arbico, Beneficial Insectary, IPM Labs., A-1 Unique Insect Control, Nature's Control, Praxis, Rincon-Vitova||see above|
|Chrysoperla spp. (predator)||M&R Durango, Florikan, Green Spot||see above|
(pink ladybird beetle)
|Arbico||aphids, caterpillars,mites, scales, thrips,
|1/sq. ft.; shipped as larvae and eggs.|
|Deraeocoris brevis (predator)||Green Spot||aphids, whiteflies, thrips|
|Arbico, IPM Laboratories, Nature's Control, Harmony Farm Supply, Hydro-Gardens, Rincon-Vitova, Praxis, Green Spot||greenhouse whitefly, sweetpotato whitefly||2000/3000 sq. ft.; temperature should be 60-85°F. Will feed on spider mites if no whiteflies are available. Should be used along with Encarsia formosa and traps.|
|Encarsia formosa (parasitic wasp)||Arbico, Nature's Control, IPM Laboratories Intl. Technology)Services, Florikan, Harmony Farm Supply, Hydro-Gardens, Natural Pest Controls, A-1 Unique Insect Control, Praxis, Rincon-Vitova, Green Spot||greenhouse whitefly, sweetpotato whitefly, silverleaf whitefly||Release 1/sq. ft. weekly for 3 weeks when pest numbers are low. Release 2-4/sq. ft. when pest numbers are high. Apply when pests are first observed. Should be used in conjunction with traps. May be used along with other beneficials. E. formosa is very susceptible to chemicals. Temps. should be at least 64°F. Re-apply every two weeks.|
|Encarsia luteola or
|Eretmocerus californicus or E. eremicus (parasitic wasp)||Beneficial Insectary, Hydro- Gardens, IPM Labs., Arbico, Praxis, Green Spot||greenhouse whitefly, silverleaf whitefly, sweetpotato whitefly||Capable of handling hot, dry temperatures. Introduce when whiteflies are first observed. May be used in combination with other beneficials such as green lacewings. Eretmocerus is more tolerant of pesticides than Encarsia formosa.|
|Harmonia axyridis (Asian lady beetle)||Green Spot||scale, whiteflies, mealybugs, aphids||Temps. should be 70-85°F; humidity around 70%.|
|Hippodamia convergens (lady beetle) (predator)||A-1 Unique Insect Control, Arbico, Caltec, IPM Laboratories, Natural Pest Controls, Nature's Control, Harmony Farm Supply, Hydro-Gardens, Praxis, Green Spot||aphids, mites, whiteflies||Release at dusk near an immediate food source. Spray plants with water prior to release.|
Appendix 2: Biorational Pesticides
|Azadirachtin—extract of neem seed; IGR that works through contact or ingestion|
|Brand Name||Supplier||Pests Controlled||REI||Application/Comments|
|Azatin||Green Spot||Aphids, caterpillars, fungus gnats, leafhoppers, leafminers, Western flower thrips, whiteflies, psyllids||4 hours||Apply when pests first appear.|
|Neemazad||Thermo Trilogy||Aphids, caterpillars, thrips, greenhouse whitefly, leafminers, sweet potato whitefly, psyllids, leafhoppers||12 hours||Cannot be applied through irrigation. Low rate can be used as a preventive.|
|Beauveria bassiana—fungus that works through contact; exposure to non-target insects should be avoided|
|Naturalis-O||SePro||aphids, caterpillars, mites, psyllids, thrips, whiteflies||4 hours||Apply when insects first appear and repeat every 7-10 days. Need good spray coverage. Not compatible with other fungicides.|
|BotaniGard||Mycotech||giant whitefly, green peach aphid, black vine weevil, others aphids and whiteflies, thrips, leafhoppers, psyllids, white grubs||12 hours||See above.|
|Garlic Gard||Soil Technologies||repels many insects||Use late in the day. Can be mixed with fish oil or horticultural oil.|
|Garlic Barrier||Green Spot||repels many insects||4 hours||Do not use in combination with bumblebees or honeybees.|
|Horticultural oil—includes dormant and summer superior oils|
|All Seasons||Green Spot||aphids, mealybugs, scales, thrips, whiteflies, spider mites||4 hours||Use on sunny days to promote rapid drying and decrease chance of phytotoxicity. Not compatible with beneficials|
|Hot pepper wax—contains capsaicin, parrafin, and mineral oil|
|Hot Pepper Wax||Green Spot||aphids, loopers, beet armyworms, mites, whiteflies, thrips, mealybugs, etc.||4 hours||Also contains herbal essential oils. Not compatible with beneficials.|
|Hot Pepper Wax||Hot Pepper Wax, Inc.||see above||0 hours|
|Insecticidal soap—contains potassium salts of fatty acids|
|M-Pede||Mycogen||aphids, mealybugs, scales, thrips, whiteflies, spider mites||12 hours||Phyotoxicity is often a concern, epseically after repeated applications.|
|Safer||Green Spot||see above||4 hours||See above.|
|Insecticidal soap||Olympic||see above|
|Neem oil— multi-purpose organic insecticide/fungicide/miticide; kills eggs, larval and adult stages of insects|
|Trilogy 90EC||Thermo Trilogy||greenhouse whitefly, silverleaf whitefly, sweetpotato whitefly, thrips, whiteflies, leafminers, aphids, mites, psyllids, San Jose scale, scale, spider mites, downy mildew, powdery mildew, Alternaria, Botrytis, etc.||4 hours||Apply at first signs of damage. Repeat every 7-10 days as needed.|
|Triact 90EC||Thermo Trilogy||see above||4 hours||For ornamental crops only.|
|PFR-97||Olympic||whiteflies, aphids, spider mites, Western flower thrips||4 hours|
|Golden Natur'l Spray Oil||Stoller||aphids, fungus gnats, lace bugs, leafminers, scales, mealybugs, spider mites, whiteflies||12 hours|
Greenhouse IPM: Sustainable Whitefly Control
By Lance Greer
NCAT Agriculture Specialist
Tiffany Nitschke, HTML Production
This page was last updated on: April 26, 2012