FORT DETRICK -- From outside, it looks like a typical greenhouse -- except for the 6-foot chain-link fence topped with barbed wire surrounding it.
The closer you look, the more unusual this greenhouse gets. There are no flowers growing inside. And the potted plants -- maybe a couple of thousand of them sitting on long, picnic-style tables -- don't look like anything you'd want to bring home to brighten a corner of your living room.
In fact, that's spiny thistle growing in there, and knapweed and leafy spurge. All common, troublesome weeds.
The U.S. Department of Agriculture operates this very special greenhouse as part of a national program to control weeds and plant pests that have hitchhiked from their native lands into the United States.
"This facility is unique in the world," said Dr. William L. Bruckart, research plant pathologist for Fort Detrick's three quarantine laboratories and greenhouse that are housed under one roof.
It is, in fact, a microbial fortress. The building has the highest level of containment for the microbes called pathogens that cause disease in plants. Inside this building, scientists are working with imported viruses, fungi, bacteria and other microorganisms that attack weeds, stunting their growth and making them sickly.
"We're working with the balance of nature," Dr. Bruckart said. "Over half the weeds in North America are introduced from outside of North America -- most brought in by accident. What we hope to do is re-establish the balance of nature by reintroducing the weed to its natural enemies.
"The reason why we contain these pathogens [in quarantine facilities] is we need to make sure they are safe around plants we consider valuable in North America" before releasing them into agricultural areas, he said.
Inside the greenhouse, researchers are testing the effectiveness of an imported rust fungus on thistle and knapweed and testing various fungi against the leafy spurge -- none posing a hazard to humans or wildlife. The weeds, which can overtake grazing pastures, have become major problems for ranchers.
"A rancher cannot go out and apply herbicide on a 10,000-acre ranch because he's making $40 an acre [from the sale of cattle], and it would cost him more than that to use the herbicide," Dr. Bruckart said.
The first known biocontrol effort in the United States dates back just over 100 years ago when an Australian ladybug was brought to California in 1889 to control the cottony cushion scale insect that was devastating orchards. The ladybug from Australia is credited with saving the citrus industry.
Dr. Bruckart says that some weed immigrants date back to the days when early American settlers, trading with Europe, weighted the bottom of their sailing vessels with soil, which contained seeds of weeds native to European countries.
Others weeds and plant pests are much newer immigrants thought to have arrived in shipments of foodstuffs or in the returning keepsakes of tourists. About once every three years, a pest that enters the United States becomes a major pest, said Dr. Richard S. Soper, national program leader for the USDA's biocontrol program.
Dr. Soper chaired a four-day meeting of scientists and regulators in Baltimore recently to discuss proposals for new regulations for importation of biocontrol agents and their release into the environment. The new regulations, which some scientists want relaxed and other scientists and some regulators want strengthened, are expected to be written later this year by the USDA's Animal and Plant Health Inspection Service.
The number of quarantine facilities in the United States has grown from six in the early 1970s to about 30 today, with more scheduled for construction, said Dr. Jack Coulson, an entomologist at the Agriculture Research Service Biological Control Documentation Center in Beltsville. The increase has resulted from successes with natural enemies of plant pests and weeds and a growing interest in finding alternatives to chemical pest control.
"Most biocontrol people do not believe that biological control will replace chemical pesticides," Dr. Coulson said. "We hope that we will cut down on the use of these. I would hope that we could replace 20 or 30 percent at least of the current chemical pesticides."
Besides being expensive, pesticides are suspected of lingering in the environment and causing some cancers and other health problems.
As the foreign pests keep slipping into the United States, more weed-controlling bugs and microbes and natural enemies of plant pests are sought out and brought in. "The growth in weed biocontrol shipments has been downright explosive," said Lloyd Knutson, director of the USDA's laboratory for the biological control of weeds in Rome. About 33 times more weed enemies were shipped to the United States last year than in 1980, he said.