Waterhemp was identified at multiple locations in the vicinity of the Red River near ND 17 (east of Grafton, N.D.) in 2015. Shawn Kasprick, manager at Simplot Company, suggested seeds may have moved into farmers’ fields following flooding in 2013.
Waterhemp continues to move north and west in 2016. Waterhemp was recently identified in Drayton Township in Pembina County, St. Andrew and Acton townships in Walsh County and Sinnott Township in Marshall County. Waterhemp was also positively identified in Bloom Township in Stutsman County.
Waterhemp is a summer annual broadleaf weed and a member of the pigweed family, the same family as redroot and powell pigweed. Waterhemp produces a tremendous amount of seed per plant that remains viable in the seed bank for four to six years. Waterhemp is native to southern and central Minnesota, Illinois and Iowa but has been carried into new geographies by ducks and geese, surface water and by people, especially via their tillage equipment and combines.
Waterhemp germinates and emerges in response to moisture in May, June, July, and even early August. A unique feature about waterhemp is male and female flowers are on separate plants (dioecious). That is, male plants produces pollen and female plants make seed. This unique biology creates tremendous genetic diversity in populations and results in plants that are biologically and morphologically unique. It also has contributed to development of biotypes that tolerate several families of herbicides, including ALS, triazine, PPO, and glyphosate. ALS (SOA 2) and glyphosate (SOA 9) tolerant biotypes are common in eastern ND and northwest Minnesota. A biotype tolerant to PPO (SOA 14) herbicides was recently identified in southern MN.
Waterhemp’s competitive advantage is in its ability to produce tremendous quantities of seed that potentially germinate and emerge after a farmer has completed postemergence herbicide applications. A few weed escapes in ‘year one’ can lead to a severe weed problem in a field by ‘year three’. The diversity of biotypes has led to populations that have differential glyphosate tolerance. Control of susceptible biotypes and failure to control more tolerant biotypes can very quickly lead to weed shifts that will result in the Roundup Ready system being less effective or ineffective in row crop fields.