Look Out for Leaf Scorch
Nurserymen and landscapers can help rein in a disease that slowly
trees including hundreds of oaks and elms in and near the historic Mall
Washington, D.C. Many of the Mall's century-old trees are infected with
bacterial leaf scorch. Nothing can be done to save them. This is also
true for "scorched"
oaks, elms, sycamores, and maples in California, Kentucky, Maryland,
New Jersey, New York, and Texas. But future generations of trees--and
tree-lovers--would benefit if nursery operators would carefully check
trees and destroy infected ones. Xylella fastidiosa bacteria cause the disease. The microbes
tree xylem, the tissue that carries water from the roots. Xylem-feeding
harbor and spread the bacteria. Warning signs of leaf scorch include
leaves that begins at their outer edges and spreads inward. Symptoms
year, spreading over the tree's crown, with stunted growth and branches
don't revive in spring. A lab test using tree sap is conclusive.
Landscapers--particularly for large projects such as
vigilant. Planting a variety of tree species may raise the odds of some
surviving an outbreak. ARS scientists in cooperation with the U.S.
the Interior have identified some control strategies. They are also
for trees with natural resistance. Jo-Ann
and Nursery Plants Research Unit, U.S. National Arboretum,
Maryland; phone (301) 504-8260.
Preemptive Strike Against Salmonella
A new product from ARS research significantly cuts the odds of
getting infected by
Salmonella microbes at the farm. The Food and Drug
recently approved use of an ARS-developed blend of beneficial bacteria
Preempt. The product was developed through a partnership between ARS
Bioscience of Dundee, Illinois, which licensed the ARS technology.
be applied in a mist to newly hatched chicks. It introduces 29 bacteria
naturally present in healthy adult chickens. The "good"
sites where Salmonella
might take hold on the chicks' intestinal walls. Instead, the
harmlessly from the chicks' bodies. In one set of field tests using
chickens, 7 percent of untreated chickens harbored Salmonella,
to 0 percent for "Preempted" birds. Studies suggest Preempt
protect chicks against listeria,
E. coli O157:H7, and campylobacter. It can be part of
measures for reducing Salmonella and other pathogen risks. But
must still be properly handled and thoroughly cooked. Most cases of
disease-causing salmonella infections in humans are traced to raw or
meat, poultry, milk, and eggs. A Preempt-like product from the same ARS
team is being tested in pigs. Donald
Corrier, USDA-ARS Food
Protection Research Laboratory, College Station, Texas; phone (409)
Dragnet for Cucumber Mosaic Virus
Growers, producers, and exporters can detect foreign and domestic
cucumber mosaic virus with a new commercial test developed from ARS
CMV attacks tomatoes, cucumbers, and many other crops. In 1992, it
tomato crop in parts of Alabama, forcing some growers out of business.
comprehensive, effective detection test might have saved some of them,
uprooting and removing infected plants is key to preventing the virus'
In earlier studies, ARS scientists collected more than 140 CMV strains
around the world. They developed antibodies that react to strains found
United States and abroad and used them as the basis for the new test.
Inc., of Elkhart, Indiana, commercialized the test. To use it, the
nursery operator touches a newly cut leaf or stem to a specially
paperlike membrane. At an agricultural extension office or laboratory,
membrane is treated with antibody-containing solutions. A color change
touched spot indicates CMV is present. The test can be used for general
detection of the virus or adapted to look for specific virus subgroups.
Hei-Ti Hsu, USDA-ARS
and Nursery Plants Research Unit, Beltsville, Maryland; phone (301)
"Science Update" was published in the June 1998
Agricultural Research magazine. Click
this issue's table of contents