|
|
|
 |
Fire ants not only build mounds in farmers' fields, but they
also are taking a bite out of farmers' seeds. ARS researchers
conducting field tests on conservation tillage in Texas saw crop
germination plummet. At first, the scientists suspected that experimental
planting equipment was damaging seeds. But when they dug up seeds
for inspection, they exposed fire ants devouring the tender, tasty
heart of the seeds. Subsequent tests have shown the ants can damage
dry wheat seed at a rate of about 11 percent per day, capable
of wiping out the entire planting in 10 days' time. Damage on
dry corn seed runs about six percent per day, grain sorghum about
seven percent daily, soybeans about one percent daily and cotton
0.5 percent per day. One possible deterrent to the foraging fire
ants: liquid starter fertilizer. When researchers used the fertilizer
at rates of about 100 pounds per acre, plants in the field emerged
without fire ant damage. In subsequent greenhouse tests, the fertilizer
wasn't as effective, but more field tests are planned this year.
Natural Resources Systems Research, Temple, TX
John E. Morrison, (817) 770-6507
Florida-grown sweet potatoes can be given a light dose of irradiation
that controls the sweet potato weevil, according to ARS researchers.
Sweet potatoes are an important crop in the southeastern United
States, and an excellent market awaits in areas where the weevil
is not present. But shipment to potato weevil-free areas such
as California is prohibited unless the product has been fumigated
with methyl bromide, the postharvest quarantine treatment approved
to kill this pest. But there's a catch: Sweet potatoes develop
fungal decay from methyl bromide, which is scheduled to be phased
out by the year 2001. Irradiation, used as a quarantine treatment
for potato weevils, leaves no residue and does not adversely affect
the taste or appearance of the sweet potatoes, even after they've
been cooked.
Subtropical
Horticulture Research Station,
Miami, FL
Jennifer Sharp, (305) 238-9321
New diagnostic tests can positively identify two types of bacteria
that attack strawberries and citrus. The tests examine the
bacteria's genetic makeup to unmask harmful strains of Xanthomonas
fragariae, which causes angular leaf spot disease in strawberries,
and Xylella fastidiosa, the culprit behind citrus variegated
chlorosis (CVC) and other economically important plant diseases.
Angular leaf spot is found throughout the United States, including
California and Florida, the major U.S. producers of strawberries,
as well as in other strawberry-growing areas of the world. It
can wipe out 80 percent of a strawberry crop. The only control
is to catch the disease at the nursery level and destroy plants.
The new DNA test will reveal the presence of the bacteria even
before symptoms appear in infected plants. Likewise, there is
no known chemical control for CVC, which has not yet arrived in
the United States but is in Brazil and northern Argentina. The
new test differentiates between strains of the bacterium that
are already in the United States and the strains that cause CVC.
Fruit Laboratory,
Beltsville, MD
John Hartung, (301) 504-7572
Bioengineered tomato plants with a one-two punch against cucumber
mosaic virus (CMV) are being field tested outdoors this summer.
ARS and collaborating scientists who engineered the tomatoes want
to see if the plants can withstand CMV more effectively--and without
chemical pesticides now used. The new tomatoes' knock-out combo
are a natural molecular parasite and a gene for CMV's protective
coat. Currently, growers in the United States and abroad spray
insecticides to kill aphids that transmit virus from plant to
plant. This doesn't always prevent disease from spreading. And,
breeders have had little success at incorporating into domestic
varieties the natural virus resistance found in some wild relatives
of tomato. But a gene for the virus' protein coat may help
"vaccinate"
tomato plants against the viral infection. The plants' second
new genetic defense is a parasite known as a viral satellite.
Little more than a naked strip of genetic material, the satellite
nevertheless is able to filch for its own use a key enzyme needed
by the virus. This retards the virus' ability to multiply and
cause disease. Neither the coat protein nor the satellite is harmful
to humans, animals or insects.
Molecular Plant
Pathology Laboratory,
Beltsville, MD
Marie E. Tousignant, (301) 504-6485
All rice plants are not created equal when it comes to naturally
fending off weeds. In ARS field tests, the Philippine rice
variety PI 312777 and two Chinese varieties--Guichow and Teqing--crowded
out up to 90 percent of weeds without help from herbicides. That's
compared to the U.S. rice variety Lemont, which kept out about
60 percent of weeds, and U.S. varieties Kaybonnet, Starbonnet
and Cypress, which slightly outperformed Lemont. The rice plants
were competing against the common weeds barnyardgrass and bearded
sprangletop for space, water, sunlight and nutrients. Rice quality
from the foreign lines usually doesn't measure up to U.S. standards.
But, their weed-fighting characteristics could be incorporated
into more desirable commercial varieties through crossbreeding,
reducing the reliance on chemical weapons against weeds.
National Rice Germplasm Evaluation and Enhancement Center, Stuttgart,
AR
David R. Gealy, (501) 673-2661
Scientists have developed ways for farmers to control disease-
and insect-carrying volunteer potatoes. Such potatoes escape
harvesting equipment in the fall, sprout the next growing season
and become a weed in subsequent crops like corn, alfalfa, onions
and carrots. While the volunteer plants compete for water, their
real threat is their role as carriers of diseases and insects.
They can harbor late blight, early blight, potato leaf roll, potato
virus Y, green peach aphids, Colorado potato beetles, and nematodes.
Strategies the scientists recommend include: maintaining and adjusting
harvesting equipment so few potatoes are left in fields; planting
varieties that mature early; planting crops like alfalfa, winter
wheat, or corn that are strong competitors; and selecting correct
herbicides. From 43,000 to 110,000 tubers per acre remain after
harvest. Scientists say up to five percent of these escapees often
survive freezing temperatures in the potato-producing sections
of central Washington and sprout to become problem plants. Tubers
survive in moist soil at 28 degrees F and in dry soil at 25 degrees
F.
Irrigated
Agriculture Research and Extension Center,
Prosser, WA
Rick A. Boydston/Marcus D. Seymour, (509) 786-3454
(Return to Table of Contents)
|
|
|
|
Printable Version
E-mail this page
