Yarrow is a summer perennial. The leaves of yarrow form alternately on the stems. The leaves are lanceolate and divided multiple times into narrow segments, appearing fern-like. The leaves of yarrow are strongly scented. The root system consists of extensive rhizomes with fibrous roots. Yarrow forms white flower heads in flat clusters. Flowering occurs from May throughout the summer. Germination occurs in mid-spring. Reproduction is by seeds and spreading rhizomes. In turf, dense patches develop due to the spreading rhizomes. Yarrow is found throughout the United States, except in the Southwest.
You can attempt to physically remove yarrow, but care must be taken to ensure that all of the rhizomes have been removed. Mowing alone will not remove yarrow, as it adapts to different mowing heights, although it becomes less competitive under lower mowing heights. Yarrow usually grows best in poor, dry, sandy soils. Proper fertility and cultural practices encourages turf to outgrow the yarrow.
Make your post-emergence herbicide application to yarrow that is actively growing and in the rosette to flower stage of growth.