The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
GULF COAST RESEARCH & EDUCATION CENTER Central Science
IFAS, UNIVERSITY OF FLORIDA Library
5007 G60T STREET EAST
BRADEITON, FL 34203 SEP 26 1988
3radenton GCREC Research Report BRA1988-15 -.Aut 1 sli o
MANAGEMENT OF THE SWEETPOTATO WHITEFLY ON TOMATO CROPS
IN SOUTH FLORIDA
James F. Price, David J. Schuster and James B. Kring1
Sweetpotato whiteflies recently have made an important impact on tomato
production in south Florida. They have caused producers to monitor their
crops for a new pest and to modify insect management practices.
Field-grown vegetables such as tomato, eggplant, melon, cucumber, pepper
and snap bean on the lower east coast were first affected in the spring
of 1987 (Schuster and Price 1987). In southwest Florida, whiteflies
(probably the sweetpotato whitefly) were first noticed on tomatoes
beginning in September 1987 but they did not increase dramatically until
February 1988 (Reggie Brown, personal communication). Populations of the
sweetpotato whitefly became extremely dense on some tomato farms in
southwest Florida during the following weeks. Ornamental crops such as
poinsettia, gerbera daisy and hibiscus were affected in 1986 (Price
Schuster and Price (1987) presented sweetpotato whitefly control and
biological information available for Florida tomato crops through August
1987. Osborne and Price (1987) provided an additional summary of
important aspects of sweetpotato whitefly identification, biology and
behavior. This paper communicates information developed since the time
of those publications.
Effective management of the sweetpotato whitefly requires that specific
action be taken when that insect first appears in a crop. Scouting a
crop at least once per week is the best way to detect the initial
appearance of the whitefly. Continued scouting provides information on
the abundance of various life stages and indicates success of current
control tactics and if additional tactics are required.
The sweetpotato whitefly may appear much like the whiteflies commonly
seen on citrus or greenhouse crops; however adults of the sweetpotato
lAssociate Professor, Professor, and Adjunct Professor of Entomology,
whitefly hold their wings tightly against their bodies and thus may
appear smaller. Sweetpotato whitefly adults have white, unmarked wings
and appear as dandruff-like flecks on the undersides of leaves. Scouts,
in their weekly inspections should look for adults resting on the
undersides of upper leaves or flying from those leaves when disturbed.
They can detect adults with yellow sticky traps placed among crop plants
Whitefly adults are monitored at the IFAS GCREC in Bradenton using 3" X
12" X 1/8" lemon yellow Plexiglass strips covered with a very thin film
of cooking oil (Butler et al. 1986). These yellow traps are placed
horizontally in the transplant production house or on plant bed surfaces
in the field for about 3 hours on bright mornings. Ihitefly adults are
attracted to the yellow strips and become stuck in the cooking oil.
Whiteflies that are the size, shape or color of known sweetpotato
whiteflies are considered "suspected sweetpotato whiteflies". Whiteflies
can not be identified conclusively in the adult form. When suspected
sweetpotato whiteflies are caught, the foliage of the crop and of known
host plants nearby is carefully inspected for immature forms that can be
identified conclusively (Hamon and Salguero 1987).
This system has been very effective to detect sweetpotato whitefly
infestations early in their development and to indicate effectiveness of
pesticides and other control measures. Population monitoring by this
method is performed by scouts trained to recognize the suspected
sweetpotato whitefly adults entrapped in oil and then to recognize
immature forms on foliage for positive identifications. The method may
not be reliable when used by less trained individuals.
Leaves found with suspected sweetpotato whitefly colonies and the skins
cast by newly emerged adults should be given to local Cooperative
Extension Service personnel to obtain reliable identifications. The
specimens should be sealed in plastic bags to prevent escape and spread
of the whiteflies.
Most biological activities of the sweetpotato whitefly occur on the
undersides of leaves. In GCREC Bradenton greenhouses, the sweetpotato
whitefly advances from the newly laid egg (period 1), through the crawler
and scale-like nymphal stages (period 2), through the pupal stage (period
3) to the newly emerged adult whitefly (period 4) in 21 days during warm
July-September temperatures and in 28 days at cooler September and
October temperatures. As temperatures decrease further, time required
for each of the developmental stages increases. Time spent in each of
the first three developmental periods is about equally divided. Under
warm, field conditions in Florida, sweetpotato whiteflies probably lay an
average of about 6-12 eggs per day.
Sweetpotato whitefly populations in tomato fields usually will contain
all life stages simultaneously. Great variability in time required for
development among individuals within a population and frequent arrivals
of adult whiteflies into the crop from the neighboring environment
ensures populations of mixed life stages. After eggs hatch, the
resulting first stage nymphs (crawlers) move a fraction of an inch away
from the egg and within a day cease to move; no further movement occurs
until the adult whitefly has emerged.
Whitefly nymphal (period 2) and adult stages (period 4) obtain food by
ingesting plant sap through sucking mouthparts. Saliva is injected into
the plant during feeding. Insect saliva predigests the food and
protects the insect's mouth parts during plant growth. Egg (period 1)
and pupal stages (period 3) do not take nourishment from host plants.
Cultural management Considerations
The best sweetpotato whitefly management begins with sound sanitation and
other cultural practices that may avoid, delay or lessen the severity of
the problem. Following are some important points of cultural management
that can have an important impact on the management of sweetpotato
whiteflies in tomato crops:
1. Crop succession. New tomato crops should not be established in or
near fields or greenhouses presently experiencing a sweetpotato
whitefly problem. Cooperation for whitefly management should be
established among neighboring vegetable and ornamental growers.
2. Whitefly movement into transplant production houses. Transplant
production houses located in regions where the sweetpotato whitefly
occurs should be enclosed where possible to exclude whiteflies. Do
not wear yellow clothing or use anything yellow in production houses
as sweetpotato whiteflies are attracted by that color and they may
hitchhike on such materials or be attracted to tomato production
3. Volunteer plants and weeds. Volunteer tomato and other crop plants
and weeds serve as excellent hosts for sweetpotato whitefly between
seasons and during production. These plants should be removed from
the environs of the tomato land well in advance of the crop.
4. Tomato transplants. A field crop can be infested by whiteflies
introduced on transplants. Therefore, transplants should be
inspected to ensure they are free of the insects before setting.
Plant production houses should be chosen for their reputation for
providing top quality material.
5. Post harvest activities. Sweetpotato whiteflies continue to develop
on tomato vines after harvest, even after irrigation to the crop has
been terminated. These insects can infest other crops and weeds in
the area And can serve as a reservoir for whiteflies in the
following season. Insecticides should be used to kill adult
whiteflies present on the plants when the harvest is complete. The
crop then should be destroyed immediately with an approved
Where sweetpotato whiteflies have become a problem in a tomato crop, crop
management practices will differ from those previously used. Such
changes, especially new insecticides chosen and new insecticide
schedules, can have an important effect on other insects and mites. In
view of these effects, tomatoes should be scouted very carefully for
various other pests and plans should be developed to respond to
additional pest problems.
Problems Associated with Insecticidal Control
Several insecticides are active against various life stages of the
sweetpotato whitefly in Florida. However, to kill a whitefly, the proper
insecticide must be delivered to the susceptible stage in the whitefly
life cycle. Fortunately, there are some insecticides that can kill
sweetpotato whiteflies at either of two life stages (Table 1). Following
are some specific problems relating to chemical control of the
1. Canopy penetration. Tomato plants form a dense canopy that is
difficult to penetrate with insecticide sprays and reach whiteflies
on the undersides of leaves. Penetration to the whitefly target on
the lower leaf surface is complicated further following each tying
2. Adherence to target insect. Adult whiteflies are covered with waxy
secretions that may reduce adherence of insecticide droplets to the
insect's living tissues.
3. Consumption of insecticide. Whiteflies are sucking insects so
insecticide residues remaining on leaf surfaces are not eaten.
Whiteflies consume only liquids from inside the plants. Thus only
systemic insecticides in plant sap are ingested by whiteflies. Eggs
and pupae do not consume any food from plants and thus are protected
from toxicity via ingestion.
4. Walking or landing on insecticide. Sucking insects such as
whiteflies may walk or land on insecticide residues and be killed.
However, only adults throughout their lives and crawlers in the
first hours in that stage are mobile. Eggs, scale-like nymphs and
pupae do not move and can not walk or land on a toxic particle.
5. Residual activity of insecticide. Immature stages of whiteflies
(except crawlers in their first few hours) are killed only when
insecticides are deposited directly on them so advantages of an
insecticides' residual activity on leaf surfaces are oftentimes
6. Insecticide resistance. Populations of sweetpotato whitefly in
various parts of the world have become resistant to some
organophosphorous and some synthetic pyrethroid insecticides
(Prabhaker et al. 1985). Uses of some important insecticides may be
lost if genes for that resistance are present in whiteflies
infesting Florida tomato crops.
Uses of Insecticides
Insecticides should be applied that kill the stages of the sweetpotato
whitefly known to be present in the field. An infested tomato field
likely would have all life stages present so weekly applications of an
insecticide effective against adults and one effective against nymphs
should be made. Alternating among insecticidal groups is essential to
reduce the chances of resistance. Following is a list of insecticides
registered on field-grown tomatoes in Florida. The insect stage on which
the insecticide is effective is indicated. New uses of any pesticide or
pesticide combination, for field-grown, fresh market tomatoes must be
approached very cautiously until uncertainties about phytotoxicity have
Table 1. Insecticides effective for control of the sweetpotato whitefly
life stages indicated and registered for use on tomatoes in
INSECTICIDAL GROUP INSECTICIDE ADULTS iWYiPHS PUPAE
Carbamate Vydate X X
Synthetic Asana X X
pyrethroid(*) Ambush, Pounce X X
Natural pyrethrum Pyrenone X X
Chlorinated Thiodan X
hydrocarbon Lindane X
Potassium salts of Safer Insecticidal
fatty acids Soap(**) X X
(*) The piperonyl butoxide synergist, Butacide, slightly enhanced the
effectiveness of these synthetic pyrethroids.
(**) Safer Insecticidal Soap has not been widely tested under Florida's
tomato production conditions.
Pesticide labels inform users how to apply pesticides effectively, safely
and legally. Always follow the label and apply pesticides only when
permitted. Never use a pesticide or method of application not thoroughly
tested for the intended production system as serious losses from plant
damage could occur. Sound judgement requires that a small portion of
each tomato variety and growth stage be treated and observed for a few
days before treating the larger production area.
(The use of trade names in this report does not constitute endorsement by
the University of Florida of one product to the exclusion of other
properly labelled products.)
Butler, G. 0. Jr., T: J. Hehneberry and W. D. Hutchison. 1986. Diology,
sampling and population dynamics of Bemisia tabaci. Agric. Zool.
Rev. 1: 167-195.
Hamon, Avas B. and Victor Salguero. 1987. Bemisia tabaci, sweetpotato
whitefly, in Florida (Homoptera: Aleyrodidae: Aleyrodinae). Fla.
Dept. Agric. and Consumer Services Div. of Plant Industry. Entomol
Circ. 292. 2 pp.
Osborne, Lance S. and J. F. Price. 1987. Pests that really bug you:
The whitefly. Grower Talks 51(2). pp. 34, 36-37, 39.
Prabhaker, N., D. L. Coudriet and D. E. ileyerdirk. 1985. Insecticide
resistance in the sweetpotato whitefly, Bemisia tabaci (Homoptera:
Aleyrodidae). J. Econ. Entomol. 78 (4): 743-52.
Price, James F. 1987. Controlling a new pest. Greenhouse Grower.
Schuster, David J. and James F. Price. 1987. New posts and possible new
insecticides for use on tomatoes. Proc. Fla. Tomato Institute.
Fla. Tomato Committee. 9pp.