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UC Pest Management Guidelines


Silverleaf whitefly adult.

Cole Crops

Silverleaf Whitefly

Scientific Name: Bemisia argentifolii (=Bemisia tabaci, Biotype B)

(Reviewed 6/07, updated 9/09)

In this Guideline:


DESCRIPTION OF THE PEST

Several species of whiteflies may infest cole crops. The most important one is the silverleaf whitefly, also known as the sweetpotato whitefly biotype B. Proper identification of silverleaf whitefly is important because other whitefly species do not cause economic damage in cole crops. Use a hand lens to examine both immatures and adults. Silverleaf whitefly adults are tiny (0.06 inch or 1.5 mm long), yellowish insects with white wings. Their wings are held somewhat vertically tilted, or rooflike, over the body and generally do not meet over the back but have a small space separating them. Greenhouse whitefly (Trialeurodes vaporariorum) adults, the species that is most similar in appearance, hold their wings flatter over the back, and there is no space between them where the wings meet in the center of the back.

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

DAMAGE

Whiteflies damage cole crops by sucking enormous quantities of sap and covering plants with sticky honeydew. Black sooty mold grows over the honeydew, lowering the photosynthetic capacity of the plant. Feeding by silverleaf whitefly stunts plant growth and development; as a result harvest may be delayed. Silverleaf whitefly feeding on broccoli causes a bleaching or whitening in stems and leaf petioles.

MANAGEMENT

Silverleaf whitefly is a major problem in California's southern desert and an increasing problem in the southern San Joaquin Valley. Biological control can be helpful in controlling light populations of this pest, and cultural practices are important in helping to prevent severe infestation. Monitor for silverleaf whitefly and apply insecticides when necessary. If whiteflies are migrating into the field, treatments to field borders may be adequate.

Biological Control
Silverleaf whitefly is an introduced pest that has escaped its natural enemies. Some native parasites and predators do attack it, but do not keep it below damaging numbers. These include several wasps in the Encarsia and Eretmocerus genera and predatory bigeyed bugs, lacewing larvae, and lady beetles that feed on nymphs. Several exotic species of parasites in the Encarsia and Eretmocerus genera also have been introduced into southern California to assist in biological control.

Cultural Control
Populations peak in late summer and begin to decrease by November. Delaying planting or using host-free periods may decrease severity of attack. When possible, plant cole crops at least one-half mile upwind from other key whitefly hosts, such as melons and cotton. Maintain good sanitation in winter and spring host plants. Attempt to produce the crop in the shortest season possible; proper management of irrigation and nitrogen will assist in this. Remove/destroy all crop residue as soon as possible.

Organically Acceptable Methods
Biological and cultural control, and sprays of insecticidal soap and narrow range oils are organically acceptable management tools.

Monitoring and Treatment Decisions
Routinely check field margins for whiteflies; these areas are usually infested first. Be especially alert for rapid population buildup when nearby host crops are in decline. During these critical periods, check cole crop fields twice weekly. Sticky traps may be useful in detecting initial whitefly migrations into fields. Allow beneficials an opportunity to control light whitefly infestations. If higher populations are present at the field margins than the field centers, then treat only the field margins. This approach will reduce treatment costs and help preserve beneficials in the field. Thresholds are not available for silverleaf whitefly in cole crops.

Effective treatments consist of combining a pyrethroid (bifenthrin-Capture) with a cyclodiene (endosulfan-Thiodan), carbamate (methomyl-Lannate), or organophosphate (acephate-Orthene, chlorpyrifos-Lorsban). Bifenthrin and endosulfan provide acceptable control of light populations when used alone, but use combinations of materials on moderate to heavy populations. An alternative to combining insecticides is to use one of the neonicotinoids (imidacloprid-Admire, or acetamiprid-Assail). Insecticidal soaps and oils are not as effective as other materials and require frequent applications and excellent coverage.

Rotate classes of insecticides to manage resistance. This includes all insecticides used in the field, including those used for other insect pests during the current season. Whitefly control with insecticides is maximized by thorough spray coverage. Ground application may give more complete coverage than air.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to natural enemies and honey bees as well as the environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. INSECTICIDAL SOAP#
  (M-Pede) 1% solution or less 12 0
  MODE OF ACTION: Contact with smothering and barrier effects.
  COMMENTS: This material has no residual and requires frequent applications and thorough coverage.
 
B. NARROW RANGE OILS
  (Saf-T-Side) 1% solution or less 4 0
  COMMENTS: For all cole crops. This material requires frequent applications and thorough coverage.
  . . . or . . .
  (Organic JMS Stylet Oil)# 3 qt/100 gal water or label rate 4 0
  COMMENTS: For cabbage and cauliflower only. This material requires frequent applications and thorough coverage.
 
NOTE: For light populations the neonicotinoids (Actara, Admire, Assail) or bifenthrin (Brigade) may be used alone. For moderate to heavy populations use either a neonicotinoid or combine bifenthrin (Brigade) with spirotetramat (Movento) or spiromesifen (Oberon).
 
C. THIAMETHOXAM
  (Actara) 3–5.5 oz 12 see comments
  MODE OF ACTION GROUP NUMBER1: 4A
  COMMENTS: PHI for head and stem Brassica is 0 days, whereas for leafy Brassica greens it is 7 days.
 
D. IMIDACLOPRID
  (Admire Pro) 7–10.5 fl oz 12 21
  MODE OF ACTION GROUP NUMBER1: 4A
  COMMENTS: Effective against nymphs only.
 
E. ACETAMIPRID
  (Assail) 70WP 1.1–1.7 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 4A
  COMMENTS: Do not apply more than once every 7 days or make more than 5 applications/season.
 
F. BIFENTHRIN*
  (Brigade) 2EC 3.8–6.4 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply in a minimum of 5 gal water/acre by air or 20 gal/acre by ground. Do not apply more than 5 applications/season.
 
G. SPIROTETRAMAT
  (Movento) 4–5 fl oz 24 1
  MODE OF ACTION GROUP NUMBER1: 23
  COMMENTS: Use following an adulticide or with an adulticide (such as bifenthrin) if adult numbers are high.
 
H. SPIROMESIFEN
  (Oberon) 2SC 7–8.5 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 23
  COMMENTS: Use following an adulticide or with an adulticide (such as bifenthrin) if adult numbers are high.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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 use on 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). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cole Crops
UC ANR Publication 3442
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgments for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside

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