He then went to the University of California, Berkeley where he studied plant nutrient systems under George Herbert Baker and received his PhD in 1981.
His dissertation focused on the nutrient system of Sagittaria, weed of plantation rice in the Central Valley of California.
He moved to Albany, California for postdoctoral research on plant competition with Lloyd Andres.
In 1983, he began work on the biological control of yellow star thistle (Centaurea solstitialis).
In 1995, he became the director of the Biological Control Laboratory USDA-ARS for Brisbane, Australia, where he led the fight against Melaleuca quinquenervia, an invasive plant in the Florida Everglades.