Around this time of year, when the feeling of spring is in the air and people are itching to play golf once again after a long winter, there might be some plants that resemble grass germinating. But beware, it is not the luck of the Irish that grass is suddenly germinating in cooler soil temperatures, it is likely prostrate knotweed.
Polygonum aviculare, also known as prostrate knotweed, is a very common weed found on golf courses across the country. Although it is a summer annual, it germinates at a soil temperature around 40 degrees Fahrenheit, providing green color to the landscape far before any cool-season turfgrass in the spring. Its initial emergence could be easily confused with turfgrass, though it eventually presents its prostrate, broadleaf nature as it matures. It can be identified by its alternate-leaf arrangement and milky sap when torn apart. Prostrate knotweed is easily confused with prostrate spurge (Euphorbia maculata), but two key differences are that spurge presents an opposite-leaf arrangement and germinates in midsummer.
Prostrate knotweed is commonly found in areas of high compaction, as it can outcompete turfgrasses in soils with a high bulk density. It is often observed right off the edges of cart paths or in other areas that encounter lots of traffic.
To best manage this tricky weed, encourage growing environments where turfgrass can naturally outcompete prostrate knotweed. If knotweed is already established on your golf course, most herbicides that have a combination of 2,4-D and triclopyr or dicamba will be effective for selectively controlling this weed in cool-season grasses. In warm-season grasses, metsulfuron will effectively control prostrate knotweed. If you have questions about how knotweed or any other weeds may affect your course, reach out to your local USGA agronomist – they may even tell you about how Course Consulting Service visits are $500 off until March 31!
Central Region Agronomists:
Zach Nicoludis, regional director, Central Region – znicoludis@usga.org
Tom Gould, agronomist – tgould@usga.org
