Late July, 2019: Mike Hunter, a Field Crops Specialist for the North Country Regional Ag Team, discovered tall waterhemp (Amaranthus tuberculatus) growing in a soybean field in Jefferson County, two counties away from the nearest known population. The farmer had purchased a combine from the Midwest, and the field was the first place he used it last fall. This find adds another New York county where growers need to be on the lookout for this aggressive agricultural weed, that is often resistant to multiple herbicide modes of action.
Waterhemp has leaves that are more elongated than other pigweeds, and have smooth stems and leaves. PSU has a very good pigweed identification website, with lots of good pictures of waterhemp and the other pigweed species.
Bryan Brown, New York State IPM’s weed management specialist, conducted a preliminary herbicide resistance trial on another waterhemp population from central NY, and believes that those populations are probably resistant to herbicide mode of action groups 2, 5, and 9. He has some IPM recommendations for waterhemp and Palmer amaranth in an IPM blog post from September 2019.
Waterhemp and Palmer amaranth both have smooth, hairless stems and leaves (occasionally just a few hairs). Our other pigweeds have hairier stems and leaves that feel rough because of their hairiness.
Elongated leaves and axial flowers of waterhemp.
Flowering head of waterhemp.