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How to Manage Pests
UC Pest Management Guidelines
Cucurbits
Whiteflies
(Reviewed 11/05,
updated 6/08)
In this Guideline:
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Several species of whiteflies infest cucurbits. Proper
identification of the whitefly species is important because the silverleaf
whitefly, and occasionally the greenhouse whitefly, represent the greatest
damage potential to cucurbits. Silverleaf whitefly is relatively new to
California and has all but displaced the sweetpotato whitefly, which was a
problem in cucurbits because of its ability to vector viruses. Silverleaf
whitefly is a major problem in California's southern desert and an increasing
problem in the southern San Joaquin Valley.
Distinguishing whitefly species is difficult; use a hand lens to
examine both immatures and adults. Whiteflies are small insects that are about
0.06 inch (1.5 mm) long. The body and wings of adults are covered with a fine,
whitish powdery wax that is opaque in appearance. Silverleaf whitefly adults
hold their wings somewhat vertically tilted, or rooflike, over the body and
generally the wings do not meet over the back but have a small space separating
them. Greenhouse whitefly (Trialeurodes vaporariorum) adults, the species that are most similar in
appearance, hold their wings flatter over the back and there is no space where
the two wings meet in the center of the back.
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. The tiny, oval eggs hatch into a first larval stage that has legs and antennae and is mobile. The
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. Silverleaf
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 filaments around the edge and the edge is somewhat vertical
where it contacts the leaf surface. Most other whiteflies found on cucurbits
produce a lot of white wax in their colonies; silverleaf whitefly has almost
none.
Desiccation of plants occurs with moderate to heavy populations and
the production of honeydew gives rise to sooty mold. The plant becomes
unthrifty and nonproductive, and the fruit is rendered unmarketable.
Sweetpotato whitefly has historically been a serious problem in cucurbits by
transmitting lettuce infectious yellows virus and squash leaf curl virus.
Recently, sweetpotato whitefly has all but disappeared in California, displaced
by the silverleaf whitefly. The silverleaf whitefly has become especially
damaging in southern California growing areas and also threatens cucurbits in
northern California. In light to moderate infestations of silverleaf whitefly,
leaves show no distinctive symptoms as a result of their feeding; however,
copious quantities of honeydew are deposited on leaves, resulting in a sticky, shiny
appearance. Silverleaf whitefly has become a serious pest because of its high
reproductive capability, wide host range, high rate of feeding, and exudation
of sticky honeydew. Its feeding on squash frequently causes crop leaves to turn
whitish
or silver,
hence the name silverleaf whitefly.
Whiteflies, with the exception of the silverleaf whitefly, rarely
require chemical control. Natural or introduced biological controls provide the
best long-term solution to keeping most of the whitefly species at low levels
along with crop host absence in the areas of heavy infestations. Key cultural
controls to prevent the buildup of this pest include the use of host-free
periods, row covers in the low deserts, silver reflective mulches, noninfested
transplants, and good field sanitation.
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.
Silverleaf 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 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.
Host-free periods are valuable for controlling several of the whitefly species.
Do not plant melons during fall in the low deserts of southern California
unless row covers are applied to beds at planting and removed at first bloom.
Row covers are not recommended in the San Joaquin Valley. Silver reflective
plastic mulches applied at planting have been shown to be effective in reducing
the number of silverleaf whiteflies landing on melon leaves. This, in turn, delays
the buildup of whitefly populations on melons. Mulches help plants off to a
healthy start and are effective until expanding foliage covers the reflective
surface.
Avoid whitefly infested transplants; this is how the silverleaf
whitefly has been transported to other areas of the state. When possible, plant
cucurbits at least one-half mile upwind from other key whitefly hosts such as
cole crops and cotton. Maintain good sanitation in winter/spring host plants
and weeds. Remove field bindweed and
other weeds in and adjacent to the crop field as well as crop residues. Attempt
to produce the crop in the shortest season possible; proper management of
irrigation and nitrogen will assist in this.
Organically Acceptable Methods
Biological and cultural controls, as well as soap and certain oil
sprays are acceptable to use in an organically certified crop.
Monitoring and Treatment Decisions
If you treat for silverleaf whitefly, make applications before pests
build up and honeydew contaminates fruit. A soil application of imidacloprid
(Admire) or thiamethoxam (Platinum) at planting and foliar treatments with
bifenthrin (Capture) or spiromesifen (Oberon) during the growing season
effectively controls whiteflies.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
|
| When choosing a pesticide, consider information relating
to water quality and impact on natural
enemies and honey bees.
|
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| A. |
SPINETORAM |
| |
(Radiant) SC |
5–10 fl oz |
4 |
1–cucumbers |
| |
MODE OF ACTION GROUP NUMBER1: 5 |
|
3–other cucurbits |
| |
| B. |
IMIDACLOPRID* |
| |
(Admire 2F) |
16–24 oz |
12 |
21 |
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MODE OF ACTION GROUP NUMBER1: 4A |
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COMMENTS: Apply at planting and incorporate into soil;
effective against nymphs only. Repeat applications of any neonicotinoid insecticide (imidacloprid-Admire;
thiamethoxam-Platinum) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an
insecticide that has a different mode of action to help delay the development of resistance. |
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| C. |
THIAMETHOXAM |
| |
(Platinum) |
|
12 |
30 |
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MODE OF ACTION GROUP NUMBER1: 4A |
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COMMENTS: Not as effective as imidacloprid but can be
substituted at planting or injected via drip irrigation during the growing
season. Repeat applications of any neonicotinoid insecticide (imidacloprid-Admire; thiamethoxam-Platinum) can
lead to resistance to all neonicotinoids. Alternate neonicotinoids with an insecticide that has a different mode of action to help delay the development of resistance. |
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| D. |
DINOTEFURAN |
| |
(Venom) 20G |
0.44–0.895 oz (foliar) |
12 |
1 |
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1.13–1.34 oz (soil) |
12 |
21 |
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(Venom) 70W |
1–4 oz (foliar) |
12 |
1 |
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5–6 oz (soil) |
12 |
21 |
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MODE OF ACTION GROUP NUMBER1: 4A |
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| E. |
BIFENTHRIN* |
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(Capture) 2EC-CAL |
4.8–6.4 oz |
12 |
3 |
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MODE OF ACTION GROUP NUMBER1: 3 |
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COMMENTS: Apply as a foliar spray to kill adults. Apply in a
minimum of 30 gal water/acre, increasing volume as plant matures. Full
coverage is necessary for best control. Toxic to bees. |
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| F. |
SPIROMESIFEN |
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(Oberon) 2SC |
7–8.5 fl oz |
12 |
7 |
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MODE OF ACTION GROUP NUMBER1: 23 |
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COMMENTS: Effective against eggs and nymphs. Apply as a foliar
treatment; thorough coverage is important. Do not make more than 3 applications/crop or apply at less than 7-day intervals. |
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| G. |
ENDOSULFAN* |
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(Thionex) 3EC |
0.66–1.33 qt |
24 |
2 |
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MODE OF ACTION GROUP NUMBER1: 2A |
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COMMENTS: There is evidence of endosulfan resistance in populations of silverleaf whitefly in the Imperial Valley. |
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| H. |
INSECTICIDAL SOAP# |
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(M-Pede) |
1% solution or less |
12 |
0 |
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MODE OF ACTION: A contact insecticide 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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| I. |
NARROW RANGE OILS# |
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(Saf-T-Side, JMS Organic Stylet Oil) |
3–6 qt/100 gal |
4 |
0 |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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COMMENTS: Oil requires frequent applications and thorough coverage. |
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UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
L. D. Godfrey, Entomology, UC Davis
C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
J. B. LeBoeuf, AgriData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa/Glenn counties
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