Palmer amaranth now has been confirmed in Huntington County as well as other nearby counties. This weed was found in at least two locations in southern Huntington County in recent weeks. It grows quickly and creates seeds very rapidly, making it hard for farmers to control.
There are 17 Indiana counties in which populations of Palmer amaranth have been found in recent growing seasons.
Initially populations of the weed were located in the northwestern counties of LaPorte, Newton, Jasper, Pulaski and Cass. Since then, more have been confirmed in Benton, Porter, St. Joseph and White counties in that part of the state, Adams, Kosciusko, Huntington and Noble counties in other northern areas, Henry in the east-central, Clay in the west, and Posey and Vanderburgh in the extreme southwest.
"Palmer amaranth is potentially the most aggressive agronomic weed Indiana producers have ever dealt with and must be managed with an aggressive control program," said Bill Johnson, Purdue Extension weed scientist.
"Seed bank populations will increase quickly in fields where Palmer amaranth is not correctly identified or managed, leading to several years of expensive control programs."
Identifying this weed can be tricky because it closely resembles three other common amaranth species: redroot pigweed, smooth pigweed and common waterhemp. They can be differentiated by the presence or lack of hair, leaf shape, petiole length, apical meristem growth pattern, seed head structures and the leaf blade watermark.
Identifying characteristics of Palmer amaranth:
• No hair.
• Leaves are wide and ovate to diamond-shaped.
• Petioles, stemlike structures that connect the leaf blade to the main stem, are as long or longer than the leaf blade itself.
• The apical meristem grows to capture as much light as possible, resulting in a rosette-like appearance when looking directly down to the top of the plant.
• Females have a long main terminal seed head that can reach up to 3 feet long.
The best method of control, Johnson said, is a multistage approach of crop rotation, thorough tillage, full rates of pre-emergence residual and post-emergence herbicides, hand weeding and monitoring ditches and field borders, and cleaning equipment before moving from infested to non-infested fields.
Bill Johnson and Travis Legleiter's publication, Palmer Amaranth Biology, Identification, and Management is available for free download from Purdue Extension's The Education Store at www.the-educa tion-store.com. Search for WS-51.
For Palmer amaranth updates, visit Purdue Extension's Pest and Crop Newsletter at extension. entm.purdue.edu/pestcrop/index.html.
Ed Farris is the agriculture and natural resource educator with the Huntington County office of Purdue Extension, he can be reached at 358-4826.