Knotweed is a pretty common weed throughout lawns, sports fields, pathways and other compacted areas. The seedling leaves are often confused with grass, allowing this weed to go untreated and to take over the landscape. As it grows, this weed produces fairly unnoticeable white to pink flowers between the stems and the leaves. The stems are red in color and can grow long , stretching out as it spreads across the area.
Apply a pre-emergent herbicide containing isoxaben as the temperatures warm up in spring to prevent this weed from emerging. Maintaining a healthy turf with dense grass is another key to stopping this summer annual from taking over the lawn. Keep the mower at an appropriate height for the particular turf grass, and use pre-emergents to stop weeds like knotweed from establishing.