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Protecting Poinsettias
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Colorful poinsettias, a favorite
plant for the holidays, are also
a favorite host for silverleaf
whiteflies. New, ARS-developed
computer software will help
growers fight this pest in
their greenhouses.
(K7244-112)
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Colorful poinsettias are America's
favorite flower for the year-end holidays. In fact, they rank as the nation's
top-selling potted flowering plant. More than 80 million poinsettias, known to
botanists as Euphorbia pulcherrima, are sold each year in this country.
Poinsettia plants are also a favorite of the silverleaf whitefly, Bemesia
argentifolii. This greenhouse pest, no bigger than the tip of a ballpoint
pen, sucks juices from poinsettia leaves and stems, according to
ARS research entomologist Gloria
DeGrandi-Hoffman. Feeding can weaken the plant.
Now, DeGrandi-Hoffman and colleagues are harnessing the analytical power of
computers to help clobber the tiny whiteflies. She has developed user-friendly
computer software called BIOCONTROL-POINSETTIA that will help poinsettia
growers determine how best to use one of their premier weapons against the
whitefly. It is a parasitic wasp, Eretmocerus eremicus, that is harmless
to humans but deadly to whiteflies. Female wasps lay their eggs in whitefly
young. Wasp young then grow inside the developing whiteflies, eventually
killing them.
DeGrandi-Hoffman did the work at the ARS Carl Hayden Bee Research Laboratory in
Tucson, Arizona. Her new computer model will help growers determine how many of
the helpful wasps they should turn loose in their greenhouses to attack the
wayward whiteflies. It will also indicate when and how often they might use the
wasps for the best control of the whiteflies. |
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Poinsettias, Euphorbia pulcherrima.
(K7244-116)
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"We anticipate that growers may
become more interested in using the wasps," says DeGrandi-Hoffman, when
whiteflies become resistant to the insecticide most commonly used today in
poinsettia greenhouses.
"The parasites are particularly important during the 6 to 8 weeks before
poinsettias go to market," she points out. "That's when the plants
get their beautiful colors. If they're sprayed then, they'll get splotches. The
model estimates the growth of the whitefly population with and without the
parasites."
DeGrandi-Hoffman developed the software at the invitation of colleagues John P.
Sanderson at Cornell University in Ithaca, New York, and Roy G. Van Driesche at
the University of Massachusetts at Amherst. |
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Computer software
developed by entomologist
Gloria DeGrandi-Hoffman
will help poinsettia
growers determine how many
beneficial parasitic wasps
they need to control
whiteflies in greenhouses.
(K9683-1)
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Sanderson, Van Driesche, and Mark
Hoddle at the University of California, Riverside, were the first to discover
the wasp's impressive capabilities as a biocontrol agent for the whitefly. But
questions about the best use of the little wasp remained. The researchers
sought out DeGrandi-Hoffman's help because of her expertise in creating similar
computer-based models.
For example, she developed a model for estimating how many individuals of two
different kinds of beneficial parasites should be put to work in alfalfa fields
to zap lygus bugs. She authored BIOCONTROL-WHITEFLY for control of whitefly on
cotton. And she authored VARROAPOP, which beekeepers can use to estimate growth
of populations of the destructive Varroa mite and to determine whether
it would be economical to apply a miticide.
DeGrandi-Hoffman's whitefly program fits easily on a single floppy disk and
runs on any personal computer that is equipped with Windows 98 or later. To
build the program, she put information about whitefly and wasp
biology—gleaned from years of experiments by Sanderson and
others—into mathematical form for the computer to analyze.
For example, the program accounts for the fact that the wasps are brought into
the greenhouse when they are pupae—the stage before adulthood—and
that they take up to 4 or 5 days to emerge. "That means the number of
wasps attacking the whiteflies may vary each day," DeGrandi-Hoffman says.
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Silverleaf whiteflies, Bemesia
argentifolii, on a leaf.
(K9678-2)
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The program also takes into account
the fact that the whitefly's reproductive rate is strongly influenced by
greenhouse temperature. That's why growers need to input the temperature of
their greenhouses as well as other basic information about their crop. For
example, they need to indicate the average number of whiteflies that are
lurking on or under the leaves of their poinsettias. They also need to estimate
how many parasites they think they want to introduce per week.
"A single release of the wasps isn't enough," DeGrandi-Hoffman
explains. One reason is that the wasps don't live long. So growers have to do
sequential releases to replenish the supply of wasps.
"The computer uses all of this information to predict the population
growth of the whiteflies in greenhouses based on the interval—such as
weekly—that wasps will be released and the number of wasps that will be
used. Growers can adjust the number of parasites and the intervals to see what
levels of control will result, then pick the best strategy," says
DeGrandi-Hoffman. "The computer augments the growers' own expertise and
experience, giving them a resource to turn to for an objective analysis."
Sanderson and Van Driesche will work with poinsettia growers in the
northeastern United States this year to test the new program further.—By
Marcia
Wood, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine (#304) and Crop
Production (#305), two ARS National Programs described on the World Wide Web at
http://www.nps.ars.usda.gov.
Gloria DeGrandi-Hoffman is with the
USDA-ARS Carl Hayden Bee Research
Center, 2000 E. Allen Rd., Tucson, AZ 85719; phone (520) 670-6380, ext.
105, fax (520) 670-6493. |
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"Protecting Poinsettias" was published in
the December
2001 issue of Agricultural Research magazine.
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