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Serving: OH
Waterhemp weeds growing in a soybean field JJ Gouin/Getty Images
PROLIFIC WATERHEMP: Palmer amaranth is not spreading much in Ohio, but waterhemp (shown here) is ubiquitous across much of the state.

Maps show waterhemp, Palmer amaranth distribution

Palmer is not spreading much in Ohio, while waterhemp is more widespread.

The Ohio State University Extension Agronomic Crops Network has developed new maps that show current knowledge of waterhemp and Palmer amaranth distribution in Ohio by the Ohio State University Extension Agronomic Crops Network.  These are based on information from a survey of OSUE county educators, along with information from samples submitted, and direct contacts, etc.  The team still considers any new introductions of Palmer amaranth to be from an external source (brought in from outside Ohio) — hay or feed; infested equipment; and Conservation Reserve Program, cover crop or wildlife seedings. 

Palmer is not really spreading around the state, and as the map shows, the team has had a number of introductions that were immediately remediated.  The number of counties where an infestation(s) is being managed is still low; and within those counties, the outbreak occurs in only a few fields still.

Map of Ohio waterhemp distribution in 2019Waterhemp is much more widespread in Ohio, and is spreading rapidly within the state from existing infestations to new areas via equipment, water, animals, etc., according to the team, which does not have ag educators in all counties. Even where there are educators, infestations can occur without knowing about them.  Producers with additional information are urged to contact the team so the maps can be updated.

Many plants called ‘pigweed’

Among the weed photos sent to the Agronomy Team members for identification, a fair number lately have been for the purposes of “pigweed” identification.  Pigweed as used here can refer to waterhemp, Palmer amaranth, spiny amaranth, Powell amaranth, and redroot or smooth pigweed (these two are mostly the same for ID and control purposes).  It’s almost impossible to tell these apart when they are very small, but it gets easier by the time they are 4 inches tall. 

Map of Ohio palmer amaranth distribution in 2019Waterhemp and smooth or redroot pigweed are still the most common, the team reports.  Waterhemp is smooth all over, with a somewhat elongated leaf with smooth edges, and leaves sometimes can be a darker and glossier green than pigweed.  Smooth or redroot pigweed will have a hairy or rough stem (more defined as it gets larger), with relatively nonglossy leaves that are widest in the middle, with “rougher” edges. 

Various resources are available to help with identification, including OSUE’s pigweed ID fact sheet and Youtube video. Identification of pigweed is not necessarily straightforward, so feel free to contact your local extension educator or OSU weed scientists ( or for help with identification.

Source: OSUE, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.
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