Agriculture: Cole Crops Pest Management Guidelines

Sweetpotato Whitefly

  • Bemisia tabaci MEAM1
  • Description of the Pest

    Several species of whiteflies may infest cole crops. Only the sweetpotato whitefly MEAM1, sometimes called silverleaf whitefly, causes economic damage. Proper identification of sweetpotato whitefly is important, because greenhouse whitefly (Trialeurodes vaporariorum) and other whiteflies do not require management in cole crops.

    Whiteflies are found mostly on the undersides of leaves. An adult whitefly is 0.06 inch (1.5 mm) long, with a yellow abdomen and thorax, and white wings. Adults fly readily when plants are disturbed.

    The tiny, oval eggs of sweetpotato whitefly hatch into translucent, mobile first instars (crawlers) that have short legs and antennae. After the first molt, nymphs lack antennae and legs, and remain fixed to the leaf surface. Older nymphs are oval and translucent, whitish, or yellowish. The last-instar nymph, also called a pupa or red-eye nymph, is the life stage most helpful for distinguishing the species.

    Use a hand lens to identify both adults and nymphs of the sweetpotato whitefly:

    Characteristic Sweetpotato whitefly Greenhouse whitefly
    Wings (at rest) Rooflike, tilted Flat, no tilt
    Wings meet along the back and entirely cover the abdomen at rest No Yes

    Sweetpotato whitefly nymphs and pupae have no filaments projecting from the edge of the body, and few or no short filaments on top. In contrast, young greenhouse whitefly nymphs have a fringe of short filaments around their perimeter, and the last-instar nymphs (pupae) have several long, projecting, waxy filaments protruding from their bodies.

    Damage

    Whiteflies damage cole crops by sucking plant sap and excreting copious honeydew that contaminates plant surfaces. Black sooty mold grows on the honeydew, which reduces photosynthesis. Sweetpotato whitefly feeding and excretions slow plant growth and development when they are numerous, which may delay harvest. Sweetpotato whitefly feeding on broccoli also causes bleaching of stems and leaf petioles, called broccoli white stem.

    Management

    Sweetpotato whitefly is a major problem in California's southern desert and the southern San Joaquin Valley. It is only a sporadic pest in the Central Coast region. Natural enemies can help to control whiteflies, and cultural practices are important in helping to prevent severe infestation. Monitor for sweetpotato whitefly and apply insecticides when warranted. If whiteflies are migrating into the crop, applying insecticide only to field borders may be adequate.

    Biological Control

    Sweetpotato whitefly is an invasive pest, and no native natural enemies in California currently provide sufficient control. Numerous parasites and predators do attack it, but generally do not keep it below damaging numbers. These natural enemies include parasitic wasps in the Encarsia and Eretmocerus genera, and predators of whitefly nymphs, such as bigeyed bugs, lacewing larvae, and lady beetles.  

    Some pathogens also attack sweetpotato whitefly, though naturally occurring infections do not typically provide sufficient control. Pathogens include the entomopathogenic fungi Beauveria bassiana, Isaria fumosorosea (Cordyceps fumosorosea) and Verticillium lecanii.

    Cultural Control

    Use the following cultural methods to control or suppress whitefly problems:

    • In regions where sweetpotato whitefly is a regular problem, delay planting or use a host-free period to decrease the severity of whitefly infestation.
      • Numbers peak in late summer and begin to decrease by November. Delaying planting until November can greatly reduce sweetpotato whitefly infestations.
    • When possible, plant cole crops at least one-half mile upwind from other key whitefly hosts, such as cotton and melons.
    • Maintain good sanitation in winter and spring by removing weeds and other alternate hosts.
    • Attempt to produce the crop in the shortest possible time to limit the extent to which whitefly numbers can increase in the crop; proper management of irrigation and nitrogen will assist in this. See the UC ANR production guide for your specific crop for more details.
    • Remove and destroy all crop residue and weed hosts of whiteflies as soon as possible (within 5 days) after harvest.

    Organically Acceptable Methods

    Use biological and cultural controls, as well as sprays of azadirachtin, entomopathogenic fungi, insecticidal soap and narrow-range oils, in an organically certified crop. The entomopathogenic fungi Beauveria bassiana and Isaria fumosorosea (Cordyceps fumosorosea) are commercially available for whitefly control. These products are most effective when used to control nymphs, and when used in combination with other insecticides. Fungicide application can reduce their efficacy.

    Insecticidal soaps and oils are not as effective as other insecticides and require frequent applications and excellent coverage.

    Monitoring and Treatment Decisions

    In areas where sweetpotato whitefly is a problem (San Joaquin Valley and low desert), monitor for whiteflies as follows (note that these periods may vary slightly from year to year):

    • From August to October:
      • If a systemic insecticide was not applied at planting, regularly (about twice weekly) check field margins for whiteflies; these areas are usually infested first.
      • If a systemic insecticide was applied at planting, check fields on a weekly basis. Begin checking twice weekly approximately 45 days after the application.
    • From November through March, check field margins once weekly.
    • Fields are commonly and uniformly infested in the low desert, but whiteflies may be more numerous along field margins during initial infestations.
    • Be especially alert for rapid increases in whitefly numbers when nearby hosts are in decline or being harvested. During these critical periods, check cole crop fields twice weekly.

    Yellow sticky traps may be useful in detecting initial whitefly migrations into fields. If using these traps, place them out of direct sunlight, with the sticky side facing the crop plants. Monitoring may also involve turning over crop leaves, as whiteflies tend to be present on leaf undersides. This method may be more difficult, as whiteflies quickly disperse when disturbed.

    Thresholds are not available for sweetpotato whitefly in cole crops. For organic cole crops or crops that did not receive an at-plant soil application of systemic insecticide, consider applying insecticide only to the field margins if whiteflies are more numerous at the field margins than the centers. This will reduce whiteflies and the costs of application, as well as help preserve natural enemies in the field. Applying insecticide to the field margins may not be necessary in cole crops that received an at-plant application of a systemic insecticide.

    Rotate insecticides with different mode-of-action group numbers to manage resistance. This includes all insecticides used in the field for other pests during the current season. Maximize the efficacy of applications by achieving thorough spray coverage. Ground application may provide more complete coverage than aerial.

    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. CYANTRANILIPROLE
    (Exirel) 13.5–20.5 fl oz 12 1
    (Verimark) 6.75–13.5 fl oz 4 NA
    MODE-OF-ACTION GROUP NUMBER1: 28
    COMMENTS: Exirel is available for a foliar application; for best performance, use an adjuvant. Verimark is available for at-plant soil application (see label for more information). Verimark translocates into the canopy of transplants 1 to 3 days after application. Effective against adults.
     
    B. CHLORANTRANILIPROLE
    (Coragen) 5–7.5 fl oz 4 3
    MODE-OF-ACTION GROUP NUMBER1: 28
    COMMENTS: Foliar application; use with an effective adjuvant for best performance. Use higher application rates within this range for heavier infestations, larger or denser crops, or extreme environmental conditions such as rainy weather or high temperatures.
     
    C. DINOTEFURAN
    (Venom) See comments 12 See comments
    MODE-OF-ACTION GROUP NUMBER1: 4A
    COMMENTS: Registered for use on broccoli, broccoflower, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, and kohlrabi. Not registered for use on cole crops grown for seed. Highly toxic to bees for more than 38 hours after application. For foliar application, application rate is 1–4 oz per acre and PHI is 7 days. For soil application, application rate is 5 oz per acre and PHI is 21 days. If a soil application is used, apply at planting. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.
     
    D. IMIDACLOPRID
    (Admire Pro) See comments 12 See comments
    MODE-OF-ACTION GROUP NUMBER1: 4A
    COMMENTS: Highly toxic to bees. Not registered for use on cole crops grown for seed. Effective against nymphs only. May be used alone for light, moderate or heavy infestations. For foliar application, application rate is 1.3 fl oz per acre and PHI is 7 days. For soil application, application rate is 4.4–10.5 fl oz per acre and PHI is 21 days. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.
     
    E. ACETAMIPRID
    (Assail 70 WP) See comments 12 See comments
    MODE-OF-ACTION GROUP NUMBER1: 4A
    COMMENTS: For head and stem cole crops, application rate is 1.1–1.7 oz and PHI is 7 days. For leafy cole crops, application rate is 1.1–2.3 oz and PHI is 3 days. May be used alone for light, moderate or heavy infestations. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.
     
    F. FLUPYRADIFURONE
    (Sivanto 200 SL) 10.5–14 fl oz 12 1
    MODE-OF-ACTION GROUP NUMBER1: 4D
    COMMENTS: Reduces both eggs and nymphs.
     
    G. SULFOXAFLOR
    (Sequoia CA) 4.25–5.75 fl oz 12 3
    MODE-OF-ACTION GROUP NUMBER1: 4C
    COMMENTS: Reduces both whitefly nymphs and eggs. Highly toxic to bees; not registered for use on crops grown for seed.
     
    H. THIAMETHOXAM
    (Actara) 3.0–5.5 oz 12 See comments
    MODE-OF-ACTION GROUP NUMBER1: 4A
    COMMENTS: PHI for head and stem cole crops is 0 days, whereas for leafy cole crops it is 7 days. May be used alone for light, moderate or heavy infestations. Not registered for use on crops grown for seed. Thiamethoxam and its metabolites (which include the neonicotinoid clothianidin) are highly toxic to bees. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.
     
    I. BIFENTHRIN
    (Brigade 2EC) 2.1–6.4 fl oz 12 7
    MODE-OF-ACTION GROUP NUMBER1: 3A
    COMMENTS: For light infestations, may be used alone. For moderate to heavy infestations, combine with spirotetramat (Movento) or spiromefesin (Oberon).
     
    J. SPIROTETRAMAT
    (Movento) 4–5 fl oz 24 1
    MODE-OF-ACTION GROUP NUMBER1: 23
    COMMENTS: Effective against nymphs. Use following an adulticide or with an adulticide (such as bifenthrin) if adult numbers are high.
     
    K. SPIROMESIFEN
    (Oberon 2 SC) 7–8.5 fl oz 12 7
    MODE-OF-ACTION GROUP NUMBER1: 23
    COMMENTS: Not registered for use on collards, kale, mizuna, or mustard greens. Effective against nymphs. Use following an adulticide or with an adulticide (such as bifenthrin) if adult numbers are high.
     
    L. BUPROFEZIN
    (Courier SC Insect Growth Regulator) 9–13.6 fl oz 12 1
    MODE-OF-ACTION GROUP NUMBER1: 16
    COMMENTS: Controls nymphs but does not reduce eggs or adults. Good coverage is essential for control. Higher application rate may be necessary for rapidly growing infestations.
     
    M. INSECTICIDAL SOAP
    (M-Pede)# 1–2% (v/v) solution 12 0
    MODE OF ACTION: Contact with smothering and barrier effects.
    COMMENTS: This insecticide has no residual activity and requires frequent applications and thorough coverage. May be phytotoxic on Brussels sprouts and cabbage. Not as effective as other insecticide options. Check with organic certifier to determine which products are organically acceptable.
     
    N. NARROW-RANGE OILS
      (Omni Oil 6)# See comments 12 0
      COMMENTS: Application rate per acre is 1 to 2 gallons in 100 gallons water (1–2% solution by volume). This insecticide requires frequent applications and thorough coverage. Check with organic certifier to determine which products are organically acceptable.
      . . . OR . . .
      (Organic JMS Stylet-Oil)# 3–6 qt/100 gal water 4 0
    COMMENTS: For cabbage and cauliflower only. This insecticide requires frequent applications and thorough coverage. Not as effective as other insecticide options. Check with organic certifier to determine which products are organically acceptable.
     
    Organic Options (Efficacy research may be lacking on these products)
    A. HEAT-KILLED BURKHOLDERIA SPP. STRAIN A396 CELLS AND SPENT FERMENTATION MEDIA
    (Venerate)# 4–8 qt 4 0
    MODE OF ACTION: biological (bacterial entomopathogen)
    COMMENTS: Option for organic growers. Most effective on whitefly nymphs, but requires two sprays to be effective. Check with organic certifier to determine which products are organically acceptable.
     
    B. ISARIA FUMOSOROSEA APOPKA STRAIN 97
    (PFR-97 20% WDG)# 2 lb 4 0
    MODE OF ACTION: biological (entomopathogenic fungi)
    COMMENTS: Registered for use on broccoli, Chinese broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, kale, and kohlrabi. Option for organic growers. May require at least two sprays of the high label rate to be effective against whiteflies. Most effective on nymphs. Does not reduce whitefly eggs. Check with organic certifier to determine which products are organically acceptable.
    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 the two intervals is the minimum time that must elapse before harvest.
    1 Rotate insecticides 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. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    # Acceptable for use on organically grown produce.
    * Permit required from county agricultural commissioner for purchase or use.
    Text Updated: 12/20
    Treatment Table Updated: 12/20