This confinement was necessary because the bacteria could be carried by insects, rain, wind, or perhaps even orchard tools, to attack new growth in the spring. They equipped them with air supply systems and bacterial filters. On April 25, 1996, van der Zwet and colleagues covered two of the trees-one copper-treated and one not-with 14- by 14-foot, clear plastic-and-pipe frames 16 feet high, creating two arborspheres. Two weeks later, two of the trees were carefully hand-painted with TennCop, a copper compound, to eliminate any surface bacteria. That treatment ensured no insects would hatch that could wound the trees' succulent new growth. Then in March 1996, they covered the trees with dormant insecticidal oil to kill any insect eggs.
In the fall of 1995, they heavily pruned the trees and removed any cankers or damaged bark that might house bacteria. "From this research, we discovered that the bacterium that causes fire blight doesn't live in a tree's older vascular system in numbers sufficient to cause disease," van der Zwet reports.įire blight infects terminal leaves on an unpruned and uncovered apple tree.įor the 6-month experiment, they used four severely blighted, 12-year-old Rome Beauty apple trees that had suffered severe fire blight nearly every year for the past 10. Michael Glenn, entomologist Mark Brown, and technician Craig Cavin set up an aseptic, whole-tree arborsphere-a kind of plastic growth chamber-experiment at the ARS Appalachian Fruit Research Station in Kearneysville.
To find out, last year van der Zwet and soil scientist D. "Despite all the research that'd been done on fire blight, we still didn't know until recently if the bacterium resides in the large scaffold limbs of an infected tree's vascular system, or if it actually reinfects the tree each season," he says. "Once it strikes, there isn't much that growers can do. "Fire blight attacks young fruit trees-especially pear and apple-causing leaves and fruit to shrivel and blacken, as though scorched by fire," says van der Zwet. Plant pathologist Tom van der Zwet has been working with fire blight at Beltsville, Maryland, and Kearneysville, West Virginia, for 30 years. Today, yet another USDA scientist is investigating uncharted territory of this bacterial disease. The fire blight bacterium, Erwinia amylovora, was later named for him. Smith and colleagues overcame the opposition and carried on additional research in the early 1900s that proved that bacteria cause diseases in many plants. Department of Agriculture scientist named Erwin F. Like Pasteur, Burrill and Arthur faced scorn and derision from distinguished scientists of their day. And by 1885, Joseph Arthur performed the experiment at Cornell University that proved the suspect bacterium was truly responsible for the disease, earning him the first Doctor of Science degree granted in America. In 1880, he discovered that the disease now known as fire blight was also associated with a bacterium. Burrill of Illinois, began working with an unknown disease that was devastating apple and pear orchards in the Midwest. It has now been well over a century since Louis Pasteur proved that bacteria can cause disease in animals.Ī few years after that well-known French scientist published his work, an American professor, T.J. This Rome Beauty apple tree inside an arborsphere at the Appalachian Fruit Research Station in Kearneysville, West Virginia, has been pruned to remove all blight cankers.
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