This tall shrubby perennial was first found in Contra Costa County in 2003 in Pacheco Slough. Subsequent surveys found it to be very scattered through Walnut Creek upstream to near Olympic Boulevard. Both County Departments of Agriculture and Public Works have been aggressive in attempts at eradication. Glyphosate and Garlon® have been used with mixed results. In June the County Department of Agriculture along with CDFA did an extensive GPS survey and treatment with Habitat®, a relatively new herbicide that is registered for use near water and is reported to be effective on purple loosestrife. The team found 220 plants on one small island in Pacheco Slough. There were about a dozen small sites of one to six plants widely scattered upstream.
We need your help in detecting this and other noxious weeds. Purple loosestrife grows 3-9 ft tall. It has beautiful spikes of pink to reddish purple flowers that can be 2-16 inches long. It blooms mid-June into September. The foliage is dense, dark green with linear shaped opposite leaves arranged alternately down the stalk. The stalk is somewhat squarish in shape. Roots form extensive mats. It grows near the waters edge of creeks and marshes. Each plant is capable of producing up to 2.5 million seeds. It can turn wetland areas and river courses into biologically sterile monocultures of loosestrife displacing all native species and has done so in vast areas of the mid west. Please keep on the lookout and report any suspects to Contra Costa County Department of Agriculture at (925) 608-6600.