By Mark Loux, Ohio State University Extension weed specialist
The maps that accompany this article show our current knowledge of waterhemp and Palmer amaranth distribution in Ohio. These are based on information from a survey of OSU Extension County Educators, along with information we had from samples submitted, direct contacts, etc. We still consider any new introductions of Palmer amaranth to be from an external source (brought in from outside Ohio) — hay or feed, infested equipment, CRP/cover/wildlife seedings. Palmer is not really spreading around the state, and as the map shows, we have had a number of introductions that were immediately remediated. The number of counties where an infestation is being managed is still low, and within those counties, the outbreak occurs in only a few fields still.
Waterhemp is much more widespread in Ohio and is spreading rapidly within the state from existing infestations to new areas via equipment, water, animals, etc. Feel free to contact us with new information to update the maps.
Among the weed photos sent to the Agronomy Team members for identification, a fair number lately has been for the purposes of “pigweed” identification. “Pigweed” as used here can refer to waterhemp, Palmer amaranth, spiny amaranth, Powell amaranth, and redroot/smooth pigweed (these two are mostly the same for ID/control purposes). It’s almost impossible to tell these apart when they are very small, but this gets easier by the time they are 4 inches tall. Waterhemp and Smooth/redroot pigweed are still the most common. 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/redroot pigweed will have a hairy/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 our pigweed ID fact sheet and Youtube video. Identification of pigweeds is not necessarily straight forward, so feel free to contact your local Extension educator or OSU weed scientists (firstname.lastname@example.org or email@example.com) for help with identification.