How to Manage Pests
UC Pest Management Guidelines
Scientific name: Bemisia argentifolii
In this Guideline:
The most common species of whitefly infesting potato is the
silverleaf whitefly. The adults are
tiny (0.06 inch, 1.5 mm long), yellowish insects with white wings. Silverleaf
whiteflies hold their wings somewhat vertically tilted, or rooflike, over the
body and the wings do not meet over the back but have a small space separating
them. Other species of whitefly have been observed in potatoes but their
populations tend to be localized within the field and do not cause damage. Populations
of silverleaf whitefly can be found relatively uniformly throughout the field
in fall plantings.
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. Mature nymphs of
silverleaf whitefly are oval, whitish, soft, and have few to no long waxy filaments.
In contrast, greenhouse whitefly, Trialeurodes
vaporariorum, has many long waxy filaments
and the edge of the body is somewhat vertical where it contacts the leaf surface.
Silverleaf whitefly damages leaves by feeding, which causes leaves
to yellow and curl, and by the production of honeydew, which causes leaves to
appear shiny or blackened (from sooty mold growing on the honeydew). Damage is
similar to that caused by aphid feeding: they debilitate the plants. Whiteflies
cause the most damage to winter-harvested potatoes in the southern San Joaquin
Valley. Fields near defoliated cotton can be severely infested.
Whitefly populations are often held in check by beneficial
insects. If populations do reach high levels, it may be necessary to treat in
Several wasps, including species in the Encarsia and Eretmocerus spp., parasitize whiteflies. Whitefly
nymphs are also preyed upon by bigeyed
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.
When possible, plant potatoes at least one-half mile upwind from
key silverleaf whitefly hosts such as melons, cole crops, and cotton. Maintain
good sanitation in areas of winter/spring host crops and weeds by destroying
and removing all crop residues as soon as possible. Control weeds in noncrop
areas including hedge rows and fallow fields and harvest alfalfa on as short a
schedule as possible. In addition, allow the maximum time between whitefly host
crops and produce vegetables and melons in the shortest season possible.
Organically Acceptable Methods
Biological and cultural controls are acceptable to use on an
organically certified crop.
and Treatment Decisions
Routinely check field margins for
whiteflies; these areas are usually infested first. Record your results (example
form. Be especially alert for rapid
population build up when nearby host crops are in decline. During these
critical periods, check fields twice weekly. If beneficials are present, allow
them 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. Treatment thresholds have not been determined for
silverleaf whitefly in potato, but potatoes can take large populations of
whitefly before treatment is necessary. If populations reach high levels in
fall, a treatment may be warranted.
|When choosing a pesticide, consider information relating
to the impact on natural
enemies and honey bees
and environmental impact Not all registered pesticides are listed. Always read label of product being used.
||Soil application: 6.5–7.5 oz
||Foliar application: 1–1.5 oz
||MODE OF ACTION GROUP NUMBER1: 4A
||COMMENTS: Do not apply more than 0.754 lb/acre/season. If an
application of imidacloprid (Admire Pro) was made at planting, choose another
treatment material with a different mode of action Group number to help prevent the development of neonicotinoid resistance.
||MODE OF ACTION GROUP NUMBER1: 2A
||COMMENTS: Apply in 100–200 gal water/acre. Do not exceed
6 applications/year or a maximum of 4 qt/acre/year. Endosulfan appears to be
effective in the San Joaquin Valley; it also is less harmful to many beneficials than organophosphate, carbamate, or pyrethroid insecticides.
UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
L. D. Godfrey, Entomology, UC Davis
D. R. Haviland, UC Cooperative Extension, Kern Co.
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