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A new, 10-minute sampling technique performed weekly during the
prime, cotton-growing season is easier, faster and more accurate
in predicting outbreaks of destructive silverleaf whiteflies.
The technique, now widely used in Arizona, California and northern
Mexico, only requires that 30 leaves in a 40- to 80-acre cotton
field be turned over and examined. Scientists used statistical
analysis to determine that samplers only need to record how many
leaves have three or more of the insects. When 57 percent fit
this definition, it is time to apply insecticide. If the average
is around 50 percent, it's time to increase sampling frequency
to every three or four days. Older methods--besides being slower--often
were not accurate, leading some growers to apply insecticide unnecessarily.
One application can cost up to $25 per acre. Silverleaf whiteflies
cost the United States about $300 million a year because of crop
losses, control costs, and other factors such as unemployment
created when insects destroy fields so they aren't worth harvesting.
U.S. Western Cotton Research Laboratory, Phoenix, AZ
Steve E. Naranjo, (602) 379-3524
Wheat germplasm from India and Mexico contain genetic resistance
to a disease that could threaten U.S. wheat exports. In a special
quarantine lab in Frederick, MD, ARS scientists confirmed that
selected varieties had resistance to Karnal bunt, a disease caused
by the fungus Tilletia indica. The selected varieties were
picked from 40,000 wheat lines taken from international germplasm
collections at Punjab Agricultural University in India, and CIMMYT
in Mexico. The selections were then screened for resistance to
Karnal bunt. This damaging disease is quarantined around the world--meaning
countries that don't have the fungus won't buy wheat from countries
where Karnal bunt is
found. So keeping the disease out of American wheat--a chief export
crop valued at $4 billion in 1994--has been a top priority. Currently,
USDA agencies are working to eradicate a Karnal bunt outbreak
that was detected earlier this year in durum wheat seeds originating
in Arizona. In the lab tests, scientists found resistant germplasm
from Mexico that was also resistant to the pathogen from Asia.
They also found resistant wheat lines from India that ward off
strains of the fungus from Mexico. By incorporating these resistant
lines into U.S. wheat, breeders might be able to protect the American
crop from Karnal bunt outbreaks such as the one in Arizona in
March 1996. The United States exported nearly 1.3 billion bushels
of wheat in 1994, making it one of the country's top crops for
overseas markets.
Foreign Disease/Weed Science Research Lab, Frederick, MD
Morris Bonde/Gary Peterson, (301) 619-2860/7313
Planting cover crops under trees and interplanting peach trees
with apple trees can cut chemical use in fruit orchards. That's
the finding from similar, cooperative studies in West Virginia
and four countries in Europe. When the trees begin to bear fruit,
strips of rape, buckwheat, dill, and dwarf sorghum planted between
tree rows play roles in controlling orchard pests. Rape is toxic
to damaging nematodes. Buckwheat flowers produce nectar and pollen
to feed beneficial insects. Flowers from dill harbor beneficial
parasites. And dwarf sorghum attracts aphids to the sorghum where
these pests become food for beneficial insects. Peach trees act
as an excellent food source for beneficial insects, when interspersed
among apples trees. An ARS lab worked out this diversified approach
that was then tested successfully in orchards in Romania, Poland,
Hungary and the Czech Republic. ARS scientists will conduct more
studies of ground cover use in Poland.
Appalachian Fruit Research Station,
Kearneysville, WV
Mark W. Brown, (304) 725-3451
A second race of the devastating golden nematode found in U.S.
potato fields will encounter formidable obstacles in new resistant
potato germplasm lines. From 1941 to 1994, it was believed that
U.S. potato growers faced only one race of golden nematode, Ro1,
found in a handful of counties in New York. Plant breeders have
provided growers with more than 30 potato varieties resistant
to Ro1. But in 1994, resistant varieties in test plots began falling
prey to another golden nematode--race Ro2. Cooperative research
between ARS and Cornell University to develop potatoes capable
of fending off other nematodes has already yielded germplasm that
is resistant to Ro2. A potato variety that resists both races
may be available for release to growers within the next five to
10 years. The golden nematode, Globodera rostochiensis,
can wipe out entire crops of potatoes by feasting on the plants'
roots. To make matters worse, each female nematode can produce
hundreds of eggs capable of lying dormant in the soil for decades,
waiting for the right soil conditions and a vulnerable potato
crop.
Plant Protection Research, Ithaca, NY
Bill B. Brodie, (607) 255-2158
Aggressive species of crop-destroying moths can spread at a rate
of eight to 113 miles a year--the majority traveling 15 to 28
miles a year. ARS scientists identified the rates for 10 foreign
species introduced into North America. This information will be
useful to scientists working on insect pest control strategies
with growers in multiple states. Moth species of the insect order
Lepidoptera have become serious pests of U.S. crops. Of the moth
species studied, the European gypsy moth spreads the slowest--an
average of about eight miles a year--probably because of its flightless
females. The browntail and satin moths, in the same family as
the gypsy moth but with flying females, spread much faster--at
26 and 28 miles per year. The fastest of the accidentally introduced
species are two cutworm moths. One travels 113 miles a year and
the other at least 99 miles in one continuous flight over water.
Researchers estimated that the time required for various introduced
species to occupy all suitable habitat in the United States and
Canada varies from 30 to 100 years. Nearly all accidentally introduced
Lepidoptera--an estimated 123 species--are of European origin.
And six of those studied came into the United States from both
the East and West coasts. Seaports, rather than airports, have
been the major points of entry.
Systematic Entomology Laboratory,
Washington, DC
Doug Ferguson, (202) 382-1777
An insect virus discovered by an ARS researcher some 30 years
ago has become a workhorse of modern biotechnology. The virus
was found in the alfalfa looper caterpillar, Autographa californica.
Today, this virus speeds research on proteins that might protect
people and animals from disease. It may also have other uses.
Scientists in more than 500 labs throughout the world employ university-
and industry-developed technology to re-tool the virus so it produces
the proteins. This safe, efficient approach often is superior
to relying on cultures of E. coli bacteria or mammalian
cells. The A. californica virus multiplies inside cultures
of insect cells in laboratory flasks. There, it yields proteins
that are closer to their natural form than those produced by E.
coli cultures. And, the insect cells are easier to raise than
mammalian cells. Meanwhile, agricultural researchers are working
to accelerate the virus' outdoor performance as an environmentally
friendly insecticide. It could protect such crops as cotton or
cabbage from their worst caterpillar enemies.
Horticultural Crops Research Laboratory, Fresno, CA
Patrick V. Vail (209) 453-3000
A simple test that detects a chemical in birch tree bark could
help plant breeders identify species and hybrids that can be used
to develop trees that are resistant to the bronze birch borer.
True birch (Betula) species are extremely difficult to identify
because of extensive hybridization in the wild or in cultivation.
ARS scientists used a simple test to determine the presence of
a chemical called platyphylloside, found in the inner bark of
birch branches. Over 500 birch trees were tested, representing
over 70 species, varieties and hybrids. Although relatively few
species or hybrids were positive for the chemical, the test enabled
scientists to confirm or suspect the identities of many birches
in major U.S. arboreta. Besides helping to identify trees that
could be used to breed resistance to the bronze birch borer, the
test uncovered evidence that the presence of platyphylloside may
make certain birches susceptible to attack by the European hornet
that causes bark stripping.
U.S. National Arboretum,
Washington, DC
Frank Santamour, (202) 245-4570
Last updated: July 10, 1996
Return to: Quarterly Report
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