Description of the Pest
Whiteflies are small flying insects that are about 0.04 inch (1 mm) long. The body and wings of adults are covered with a fine whitish powdery wax that is opaque in appearance. Whiteflies colonize the underside of leaves; adults and eggs are commonly found on the lower surface of younger leaves and the scalelike nymphal stages on somewhat older leaves.
Distinguishing whitefly species is difficult; use a hand lens to examine both immatures and adults. Adult silverleaf whiteflies, sometimes called sweetpotato whiteflies, hold their wings somewhat vertically tilted like the peaked roof of a house, instead of flat over their bodies like the greenhouse whitefly. During the last part of the fourth larval stage, often called the pupa, whiteflies develop red eyes and stop feeding. The pupal stage is the stage that is easiest to identify silverleaf whitefly; pupae have no waxy filaments around their edges as do most other species of whiteflies.
Damage
Extremely dense populations of silverleaf whitefly may immigrate into late-August or September plantings of carrots in the low deserts of southern California and damage seedlings. In light to moderate infestations, leaves show no distinctive symptoms as a result of whitefly feeding; however, copious quantities of honeydew are deposited on leaves, resulting in a shiny, sticky appearance.
Management
Whiteflies can be very difficult to control with insecticides. Natural or introduced biological methods provide the best long-term solution to keeping whitefly numbers at a minimum along with reducing host plants in areas of heavy infestation. If you treat for silverleaf whitefly, make applications before pests build up and contaminate carrot tops with honeydew.
Biological Control
Several parasitic wasps, including species in the Encarsia and Eretmocerus genera, control whiteflies. Whitefly nymphs are also preyed upon by bigeyed bugs, green lacewing larvae, brown lacewing larvae and lady beetles. Encourage buildup of beneficial insects by avoiding the use of nonselective pesticides and by protecting their habitat.
Cultural Control
Remove field bindweed and other weeds in and adjacent to the crop field as well as crop residues. Host-free periods are valuable for controlling several of the whitefly species.
Organically Acceptable Methods
Use biological controls, cultural controls, and soap sprays (potassium salts of fatty acids) in a certified organic crop.
Monitoring and Treatment Decisions
Carrots are not a preferred host of whiteflies and in some areas treatment with insecticides is rarely justified. Where silverleaf whitefly is a chronic problem, a treatment with imidacloprid at planting will effectively control whiteflies during the critical period of stand establishment. If treatment is not applied at planting, occasionally dense colonies of silverleaf whitefly nymphs can necessitate treatment of bunching carrots to prevent honeydew and sooty molds from severely contaminating the carrot tops.
For foliar treatment, combinations of a pyrethroid insecticide (mode-of-action group 3A) with methomyl provide superior control over applications of a single insecticide. Rotate pyrethroid treatments with a treatment of insecticidal soap to help slow development of insecticide resistance. Insecticidal soaps control all immature stages of whiteflies, including eggs, whereas the other insecticides control first instar nymphs and adults only; thus, treatment timing is critical.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites | Predators 4 | Parasitoids 4 | Residue duration 5 | Leaching(fish) 6 | Adsorbed runoff(fish) 7 | Solution runoff(fish) 8 | Leaching(human) 9 | Solution runoff(human) 10 | Last updated 11 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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|
Asana XL | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
5.8–9.6 fl oz | 12 | 7 | Tank mix with methomyl product. Apply as... | broad | — | moderate | high | moderate | high | intermediate | extra high | low | intermediate | 09/2024 | ||
|
|
Admire Pro | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4A |
4.4–10.5 fl oz | 12 | 21 | Apply at planting to control migrating w... | narrow | — | — | — | — | — | — | — | — | — | 09/2024 | ||
|
|
Leverage 360 | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4A/3A |
2.8 fl oz | 12 | 7 | Do not spray directly or allow to drift... | broad | — | — | high | high | moderate | — | — | — | — | — | 09/2024 | |
| Lannate SP | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
1A |
0.5–1 lb | 48 | 1 | Tank mix with esfenvalerate product. | broad | — | high | high | moderate | — | — | — | — | — | 09/2024 | |||
|
|
M-Pede # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
— |
1% solution or less | 12 | 0 | Insecticidal soap. This material has no... | broad | — | low | low | short | low | intermediate | intermediate | very low | low | 09/2024 | ||
|
|
Actara | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4A |
3.0–4.0 fl oz | 12 | 7 | Do not spray directly or allow to drift... | narrow | — | moderate/high | moderate/high | moderate | very low | very low | low | high | high | 09/2024 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- * a Permit required from county agricultural commissioner for purchase or use.
- # ↩ Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 5 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 6 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 7 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438
D.R. Haviland, UC IPM and UC Cooperative Extension Kern County
E.T. Natwick (emeritus), UC Cooperative Extension Imperial County
J.K. Sidhu, UC Cooperative Extension Kern County
Acknowledgement for Contributions to Invertebrates
W.E. Chaney (emeritus), UC Cooperative Extension Monterey County
C.G. Summers (emeritus), Entomology, UC Davis and Kearney Agricultural Research and Extension Center, Parlier
