FREDERICK -- Researcher Rick Bennett is spending four months this year traveling Europe looking for sick weeds.

The U.S. Department of Agriculture (USDA) plant pathologist is looking for diseases to kill Mediterranean and Eastern European weeds brought over by immigrants over the past 500 years.

Many of this nation's worst weeds were brought unwittingly more than 100 years ago by settlers bringing seeds to grow crops here, but the weeds' natural enemies were left at home, said Mr. Bennett, who is based at USDA laboratories at Fort Detrick.

Until July 28, he will be looking for weeds with diseases that can be brought back and safely used to combat thistles, leafy spurges and other scourges of the Western Hemisphere.

Mr. Bennett plans to bring back about 200 samples of plant diseases that will be studied in a quarantined greenhouse for up to 10 years. If the sample kills more than its target weeds, the research stops, he said.

The samples will be carefully transported using double packaging.