Knotweed germinating next to sidewalks and other hotspots – Turfgrass Science at Purdue University

Knotweed germinating next to sidewalks and other hotspots

Prostrate knotweed is currently germinating in thin areas next to sidewalks, cart paths, driveways and other hotspots. Knotweed is often confused with crabgrass at this early stage. Knotweed leaves have rounded leaf tips whereas crabgrass has leaf tips that come to a dull point (See photos). Crabgrass also has veins running lengthwise (parallel veination) whereas knotweed’s veins are not as obvious and they are more perpendicular to the length of the leaf. Crabgrass won’t be germinating in the hotspots for another few weeks depending on the weather. Control of knotweed at this small stage can be had with most postemergence broadleaf herbicides. Since knotweed will continue to germinate for the next few months, multiple applications of postemergence herbicides are required because they have no residual (preemergence) control. Marginal residual control can be obtained from crabgrass preemergence herbicides, but isoxaben-containing products (Gallery or Snapshot) provide the best residual control.


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