Government contractor DynCorp International Inc. has escaped a suit over injuries purportedly caused by anti-narcotic herbicides sprayed at the Colombia-Ecuador border, after a Washington, D.C., judge determined the plaintiffs could not establish causation, according to an opinion unsealed Tuesday. Judge Richard W. Roberts determined that the plaintiffs — approximately 2,000 Ecuadoreans bringing negligence and tort claims for acute and chronic injuries related to herbicide exposure — failed to establish the reliability of key expert witness Dr. Michael Wolfson…