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How to Manage Pests
UC Pest Management Guidelines
Cole Crops
Silverleaf Whitefly
Scientific Name: Bemisia argentifolii
(Reviewed 6/07,
updated 6/07)
In this Guideline:
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Several species of whiteflies may infest cole crops. 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.
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.
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) |
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| When choosing a pesticide, consider information relating
to the impact
on natural enemies and honey bees and environmental impact.
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| A. |
INSECTICIDAL SOAP# |
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(M-Pede) |
1% solution or less |
12 |
0 |
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MODE OF ACTION: Contact with smothering and barrier effects. |
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COMMENTS: This material has no residual and requires frequent applications and thorough coverage. |
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| B. |
NARROW RANGE OILS |
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(Saf-T-Side) |
1% solution or less |
4 |
0 |
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COMMENTS: For all cole crops. This material requires frequent applications and thorough coverage. |
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...or... |
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(Organic JMS Stylet Oil)# |
3 qt or label rate |
4 |
0 |
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COMMENTS: For cabbage and cauliflower only. This material requires frequent applications and thorough coverage. |
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| NOTE: For light
populations the neonicotinoids (Assail, Admire) or bifenthrin (Capture) may
be used alone. For moderate to heavy populations use either a neonicotinoid
or combine bifenthrin (Capture) with methomyl (Lannate), acephate (Orthene), or chlorpyrifos (Lorsban). |
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| C. |
ACEPHATE |
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(Orthene) 75S |
Label rates |
24 |
14 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: For use on Brussels sprouts and cauliflower. Do not apply more than 8 lb/acre/season to Brussels sprouts. |
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| D. |
ACETAMIPRID |
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(Assail) 70WP |
1.1–1.7 oz |
12 |
7 |
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MODE OF ACTION GROUP NUMBER1: 4A |
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COMMENTS: Do not apply more than once every 7 days or make more than 5 applications/season. |
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| E. |
BIFENTHRIN* |
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(Capture) 2EC |
3.8–6.4 fl oz |
12 |
7 |
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MODE OF ACTION GROUP NUMBER1: 3 |
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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. |
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| F. |
CHLORPYRIFOS |
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(Lorsban) 50W |
2 lb |
24 |
21 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: To avoid phytotoxicity, do not treat plants that are
under extreme heat and drought stress. Do not apply more than 6 times/season. Avoid drift and tailwater runoff into surface waters. |
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| G. |
IMIDACLOPRID |
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(Admire Pro) |
7–10.5 fl oz |
12 |
21 |
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MODE OF ACTION GROUP NUMBER1: 4A |
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COMMENTS: Effective against nymphs only. |
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| H. |
METHOMYL* |
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(Lannate) 90SP |
0.25–1 lb |
48 |
see comments |
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MODE OF ACTION GROUP NUMBER1: 1A |
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COMMENTS: Short residue; most effective against adults. Do not
graze or feed to livestock. Preharvest interval is 3 days for broccoli,
Brussels sprouts, and cauliflower and 1 day for cabbage. See label for other cole crops. |
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UC IPM Pest Management Guidelines: Cole Crops
UC ANR Publication 3442
Insects
W. E. Chaney, UC Cooperative Extension, Monterey Co.
E. T. Natwick, UC Cooperative Extension, Imperial Co.
Acknowledgments for contributions to the insects section:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
N. C. Toscano, Entomology, UC Riverside
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