Agriculture: Lettuce Pest Management Guidelines

Sweetpotato Whitefly

  • Bemisia tabaci MEAM1 (formerly B biotype)
  • Description of the Pest

    Several species of whiteflies may infest lettuce. Only sweetpotato whitefly can cause economically important damage. Use a hand lens to distinguish sweetpotato whitefly from other whiteflies by examining both immature and adult stages.

    Sweetpotato whitefly
    (Bemisia tabaci MEAM1)
    Greenhouse whitefly
    (Trialeurodes vaporariorum)
    Bandedwinged whiteflies
    (Trialeurodes abutiloneus)
    Adults are 0.06 inch (1.5 mm) long, yellowish insects with white wings. Adults are 0.06 inch (1.5 mm) long and very similar to sweetpotato whitefly. Adult are approximately 0.04 inch (1 mm) long, pale yellow.
    Their wings are held somewhat vertically tilted, or "rooflike", over the body and generally do not meet over the back but have a small gap separating them. Adults hold their wings flatter over the back and there is no space where the two wings meet in the center of the back. Adults have brownish bands across their wings. At rest, wings are held flat.

    Whiteflies are found mostly on the undersides of leaves. They fly readily when plants are disturbed. The tiny, oval eggs hatch into a first larval stage that has legs and antennae and is mobile. Both legs and antennae are lost after the first molt and subsequent stages remain fixed to the leaf surface. The last nymphal stage, often called the pupa or the "red-eye" nymph, is the stage that is easiest to identify. Sweetpotato whitefly pupae are oval, whitish, and soft. The edge of the pupa tapers down to the leaf surface and has few to no long waxy filaments around the edge. In contrast, greenhouse whitefly pupae have many long waxy filament around the edge and the edge is somewhat vertical where it contacts the leaf surface.

    Damage

    Sweetpotato whitefly is a major pest in the low desert lettuce production areas both due to direct feeding damage and virus transmission. It is not a major pest in the Salinas and San Joaquin Valleys. It does not occur on spring lettuce and generally only very low numbers occur on fall lettuce. Feeding by whiteflies produces sticky honeydew on the leaves. A black, sooty mold can often develop on the excreted honeydew. Sweetpotato whitefly feeding may cause a stunting and yellowing of head lettuce.

    Management

    Biological Control

    Several wasps, including species in the Encarsia and Eretmocerus genera, parasitize whiteflies. Whitefly nymphs are also preyed upon by bigeyed bugs, lacewing larvae, and lady beetles. Sweetpotato whitefly is an introduced pest that has escaped its natural enemies. Some indigenous native parasites and predators do attack it, but do not keep it below damaging numbers. The lady beetle Delphastus pusillus is being introduced into southern California to enhance biological control in the area.

    Cultural Control

    Plant your earliest lettuce at least one-half mile upwind from cotton, melon, or cole crop fields. Maintain proper field sanitation by destroying crop residues that may harbor whiteflies after harvest. Remove weed that host the whitefly and virus. Whitefly numbers in desert areas decrease in mid-October and November, so whenever possible, delay planting to avoid infestation. Present research indicates sprinklers may reduce whitefly numbers and virus incidence.

    Organically Acceptable Methods

    Use biological and cultural controls and sprays of azadirachtin or entomopathogenic fungus in an organically certified crop.

    Monitoring and Treatment Decisions

    To prevent sweetpotato whitefly infestation:

    • Routinely check field margins for whiteflies; these areas are usually infested first.
    • Be especially alert for rapid number increase when nearby host crops senesce (dry out) or are harvested. During these critical periods, check lettuce fields twice weekly.
    • Use sticky traps to detect initial whitefly migrations into fields.
    • Allow natural enemies an opportunity to manage light whitefly infestations.
    • When higher numbers are present at the field margins and not the field centers, use targeted insecticide applications only to the field margins which will slow movement of whiteflies into the field for a short period. This approach will reduce treatment costs and help preserve natural enemies in the field.

    Thresholds are not available for sweetpotato whitefly in lettuce.

    The most effective treatment is to apply imidacloprid (Admire) at planting. This application will provide control in fields where sweetpotato whitefly problems are anticipated.

    Whitefly control with insecticides is maximized by thorough spray coverage. Ground application may give more complete coverage than air.

    Common name Amount per acre** REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
    A. FLUPYRADIFURONE
    (Sivanto Prime) 10.5–12 fl oz 12 1 (foliar)
    MODE-OF-ACTION GROUP NUMBER1: 4D
    COMMENTS: Apply as a foliar spray. Works best following DINOTEFURAN (Venom) soil injection treatment at planting.
    B. IMIDACLOPRID
    (Admire Pro) 7–10.5 fl oz 12 21
    MODE-OF-ACTION GROUP NUMBER1: 4A
    COMMENTS: Soil application. Placement is critical to successful control; see label for details. Do not apply more than 0.38 lb a.i. AdmirePro/acre per year.
    C. DINOTEFURAN
    (Venom) 0.44–0.67 lb (foliar)
    12 7 (foliar)
    1.13–1.34 lb (soil) 21 (soil)
    MODE-OF-ACTION GROUP NUMBER1: 4A
    D. THIAMETHOXAM
    (Platinum) 5–11 fl oz 12 30
    (Actara) 5 fl oz 12 7
    MODE-OF-ACTION GROUP NUMBER1: 4A
    E. SPIROTETRAMAT
    (Movento) 4–5 fl oz 24 3
    MODE-OF-ACTION GROUP NUMBER1: 23
    F. SPIROMESIFEN
    (Oberon 2SC) 7–8.5 fl oz 12 7
    MODE-OF-ACTION GROUP NUMBER1: 23
    G. BIFENTHRIN* 0.08–0.1 lb a.i. 12 7
    (Capture LFR) 6.8–8.5 fl oz
    MODE-OF-ACTION GROUP NUMBER1: 3A
    COMMENTS: For use on head lettuce only. Apply in a minimum of 20 gal water/acre by ground. Apply weekly or as needed with a maximum of four applications per season. Reentry interval is 7 days after application, unless protective clothing is worn. Do not use if leafminers are present.
    ** Mix with enough water to provide complete coverage.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
    * Permit required from county agricultural commissioner for purchase or use.
    # Acceptable for organically grown produce.
    1 Rotate chemicals 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; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 04/17
    Treatment Table Updated: 04/17