Prostrate knotweed is an annual, common along sidewalks in turf or wherever turf is stressed and less vigorous. It thrives in dry, compacted soils or wherever there is excessive foot traffic. The plant forms a tough, wiry mat of stems and leaves. To differentiate from spurge, a broken stem does not produce a milky sap. Flowers are small, white, and inconspicuous. They are found where the leaf meets the stem. This weed produces many seeds. Annual core aeration in spring and/or fall will reduce knotweed infestation. Control Pre-emergent herbicides can be effective if applied in late fall/winter (knotweed can germinate in Feb or March). Post-emergent herbicides are mostly ineffective after plants become larger. 2,4-D and 2,4-D combinations will give fair control when applied to younger plants.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010