Science Update

Look Out for Leaf Scorch

Nurserymen and landscapers can help rein in a disease that slowly  dooms trees including hundreds of oaks and elms in and near the historic Mall  in 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,  Nebraska, New Jersey, New York, and Texas. But future generations of trees--and tree-lovers--would benefit if nursery operators would carefully check  young trees and destroy infected ones. Xylella fastidiosa bacteria cause the disease. The microbes  clog tree xylem, the tissue that carries water from the roots. Xylem-feeding  insects harbor and spread the bacteria. Warning signs of leaf scorch include  browning of leaves that begins at their outer edges and spreads inward. Symptoms  recur each year, spreading over the tree's crown, with stunted growth and branches  that don't revive in spring. A lab test using tree sap is conclusive. Landscapers--particularly for large projects such as  subdivisions--should be vigilant. Planting a variety of tree species may raise the odds of some surviving an outbreak. ARS scientists in cooperation with the U.S.  Department of the Interior have identified some control strategies. They are also  searching  for trees with natural resistance. Jo-Ann Bentz, USDA-ARS Floral and Nursery Plants Research Unit, U.S. National Arboretum,  Beltsville, Maryland; phone (301) 504-8260.

Preemptive Strike Against Salmonella

A new product from ARS research significantly cuts the odds of  chickens' getting infected by  Salmonella microbes at the farm. The Food and Drug  Administration recently approved use of an ARS-developed blend of beneficial bacteria  called Preempt. The product was developed through a partnership between ARS  and MS Bioscience of Dundee, Illinois, which licensed the ARS technology.  Preempt can be applied in a mist to newly hatched chicks. It introduces 29 bacteria naturally present in healthy adult chickens. The "good"  bacteria block sites where Salmonella  might take hold on the chicks' intestinal walls. Instead, the  pathogens pass harmlessly from the chicks' bodies. In one set of field tests using  80,000 chickens, 7 percent of untreated chickens harbored Salmonella,  compared to 0 percent for "Preempted" birds. Studies suggest Preempt  also helps protect chicks against listeria,  E. coli O157:H7, and campylobacter. It can be part of  comprehensive measures for reducing Salmonella and other pathogen risks. But  the meat must still be properly handled and thoroughly cooked. Most cases of disease-causing salmonella infections in humans are traced to raw or  undercooked meat, poultry, milk, and eggs. A Preempt-like product from the same ARS  research team is being tested in pigs. Donald Corrier, USDA-ARS Food  Animal Protection Research Laboratory, College Station, Texas; phone (409) 260-9484. 

Dragnet for Cucumber Mosaic Virus

Growers, producers, and exporters can detect foreign and domestic  strains of cucumber mosaic virus with a new commercial test developed from ARS  research. CMV attacks tomatoes, cucumbers, and many other crops. In 1992, it  plagued the tomato crop in parts of Alabama, forcing some growers out of business.  A comprehensive, effective detection test might have saved some of them,  because uprooting and removing infected plants is key to preventing the virus'  spread. In earlier studies, ARS scientists collected more than 140 CMV strains  from around the world. They developed antibodies that react to strains found  in the  United States and abroad and used them as the basis for the new test.  Agdia, Inc., of Elkhart, Indiana, commercialized the test. To use it, the  farmer or nursery operator touches a newly cut leaf or stem to a specially  coated, paperlike membrane. At an agricultural extension office or laboratory,  the membrane is treated with antibody-containing solutions. A color change  at the 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   Floral  and Nursery Plants Research Unit, Beltsville, Maryland; phone (301) 504-5657. 

"Science Update" was published in the June 1998  issue of Agricultural Research magazine. Click here  to see this issue's table of contents