Prostrate Knotweed

Biology of Prostrate Knotweed

Prostrate knotweed (Polygonum aviculare), an early germinating summer annual broadleaf, commonly appears in low-oxygen soils. These include compacted areas next to sidewalks and previously flooded areas. In many Midwest states, germination begins in late February and early March.

Identifying Prostrate Knotweed

In Indiana, it is the first summer annual weed to germinate, often appearing next to driveways and sidewalks. Observations over the past three years show its initial germination in late-February or early March. The young weeds display a red hypocotyl. The seed leaves, or cotyledons, are very narrow, making them resemble germinating grass at first glance. As the plants mature, they become tough, wiry, and adopt a prostrate growth pattern.

Cultural Control Methods

To combat it effective to reduce soil compaction through aerification. Additionally, improving drainage in flood-prone areas can significantly help.

Biological Control Options

Currently, there are no known biological control methods.

Chemical Control in Cool-Season Turf

For chemical control, 2,4-D alone offers fair control. However, combining it with triclopyr or dicamba enhances effectiveness, providing excellent control. Several products, including Trimec 992 and SpeedZone, contain 2,4-D and dicamba. Products like 4-Speed XT and TZONE combine 2,4-D with triclopyr.

Chemical Control in Warm-Season Turf

In warm-season turf, metsulfuron or the previously mentioned herbicides are effective for postemergence control of prostrate knotweed.

Preemergence Control Strategies

For preemergence control, isoxaben applied in late fall (November or December) is effective. Other preemergence herbicides also work but are less effective than isoxaben. While late winter applications of isoxaben are possible, they are less ideal due to unfavorable spraying conditions and the difficulty in predicting the exact timing of prostrate knotweed germination, typically in early March.