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Waterhemp found in Jefferson County

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.

Creeping Buttercup in Corn

Photo provided by Mike Hunter of CCE Jefferson County.

The mystery weed

This weed was found in late May in a wetter portion of a corn field. The grower has had it in the field for several years, and while it is not yield limiting, control with his normal weed management plan has not been effective.

 

Photos by Leslie J Mehrhoff of the University of Connecticut, via the bugwood.org image library.

Identification

This is creeping buttercup (Ranunculus repens). There are several weedy buttercups, but this one has three lobes on it leaves and aboveground stolons – aboveground runners – that it uses to spread. It’s a perennial that’s often found in wet areas of pasture, farmland, or roadsides. It is toxic to livestock when fresh. While it is not very palatable, it’s reported that occasionally livestock develop a taste for it and injest fatal doses. It is not toxic in hay; I did not see data on its toxicity in wet feeds such as sileage. Most of the information available is from the Pacific Northwest, such as this article from the state of Washington.

Management

Control of creeping buttercup can be obtained through regular cultivation in drier conditions, repair of the drainage in the infested field, spot pulling or spraying, and herbicides. Purdue University produced a good summary of agricultural control of buttercup through herbicides. Mike Hunter of CCE’s field crops team did a quick check of corn herbicides with this weed listed on the label, and found Banvel (and many other generic dicambas), Diflexx Duo, Distinct, Fexapan, Roundup Xtend, and Xtendimax.