Harvest weed seed control of Italian ryegrass (Lolium perenne ssp multiflorum), common ragweed (Ambrosia artemisiifolia), and Palmer amaranth (Amaranthus palmeri)

Authors: BEAM, SHAWN - Virginia Tech; Mirsky, Steven; CAHOON, CHARLIE - North Carolina State University; HAAK, DAVID - Virginia Tech; FLESSNER, MICHAEL - Virginia Tech

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2019
Publication Date: 8/21/2019
Citation: Beam, S.C., Mirsky, S.B., Cahoon, C., Haak, D., Flessner, M. 2019. Harvest weed seed control of Italian ryegrass (Lolium perenne ssp multiflorum), common ragweed (Ambrosia artemisiifolia), and Palmer amaranth (Amaranthus palmeri). Weed Technology. 33(4):627–632.

Interpretive Summary: Harvest Weed Seed Control (HWSC), in which farmers prevent weeds from successfully adding more seeds to the existing bank of seeds in the soil is being targeted for herbicide-resistance management. This study investigated the use of HWSC in Virginia, in 2017-2018, targeting the weed, Italian ryegrass in continuous winter wheat as well as the weeds common ragweed and Palmer amaranth in continuous soybean. HWSC reduced Italian ryegrass tillers compared to the conventional harvest at two locations in April (29 and 69%), but no difference was observed at a third location. At wheat harvest, HWSC at one location reduced Italian ryegrass seed heads (41 seed heads m-2) compared to conventional harvest (125 seed heads m-2). In soybean, HWSC initially reduced common ragweed densities by 22 and 26%, respectively. By soybean harvest, no differences in common ragweed density, seed retention, or crop yield were observed, due to effectiveness of herbicides that were applied after soybean planting. Overall, HWSC was demonstrated to be a viable method to reduce Italian ryegrass and common ragweed populations. This finding is valuable to farmers struggling with the rise of herbicide resistance in these weed species since it provides an avenue for weed control that does not negatively impact other aspects of their cropping system (i.e., the way a return to tillage for weed control would decrease soil health).

Technical Abstract: Herbicide resistance is a major problem in US and global agriculture, driving farmers to consider other methods of weed control. One of these methods is harvest weed seed control (HWSC), which has been demonstrated to be effective in Australia. Studies were conducted across Virginia in 2017 and 2018 targeting Italian ryegrass in continuous winter wheat as well as common ragweed and Palmer amaranth in continuous soybean. Studies assessed HWSC (via weed seed removal) on weed populations in the next year’s crop compared to conventional harvest (weed seeds returned). HWSC reduced Italian ryegrass tillers compared to the conventional harvest at two locations in April (29 and 69%), but no difference was observed at a third location. At wheat harvest, HWSC at one location reduced Italian ryegrass seed heads (41 seed heads m-2) compared to conventional harvest (125 seed heads m-2). In soybean prior to preplant herbicide applications and postemergence (POST) herbicide applications, HWSC reduced common ragweed densities by 22 and 26%, respectively, compared to the conventional harvest plots. By soybean harvest, no differences in common ragweed density, seed retention, or crop yield were observed, due to effectiveness of POST herbicides. No treatment differences were observed at any evaluation timing for Palmer amaranth, which is attributed to farmer weed management (i.e., effective herbicides) and low weed densities making any potential treatment differences difficult to detect. Across wheat and soybean, there were no differences observed with crop yield between treatments. Overall, HWSC was demonstrated to be a viable method to reduce Italian ryegrass and common ragweed populations.