Written by: Nevin Lawrence and Chabella Guzman.
Dry edible bean production in Nebraska ranks first in Great Northern beans and second in pinto beans. The Panhandle of Nebraska, where the bean industry is concentrated, generates tens of millions of dollars for the state's agricultural economy.
University of Nebraska-Lincoln Panhandle Research Extension and Education Center Dr. Nevin Lawrence, Nebraska Extension Weed Management, is researching suppression of the weed Palmer Amaranth. The weed is herbicide-resistant and one of the most severe threats to Nebraska dry bean producers. Currently, there are no effective post-crop emergence (POST) herbicides labeled in dry beans that can control ALS- and glyphosate-resistant Palmer amaranth.
Along with herbicides, Lawrence is researching options beyond herbicides. Results from a Nebraska Dry Bean Commission funded project in 2020 indicated that planting a winter cereal cover crop can completely suppress Palmer amaranth in dry edible beans without the use of a POST herbicide and without negative impacts to crop yield. However, planting a winter cereal before dry edible beans is challenging as corn is the predominant crop planted the year before dry beans, and corn is harvested in October – December. By the time corn is harvested, it is too late to establish a fall-planted cover crop. Another option is to plant a spring seeded cover crop; however, both the practicality of establishing a spring seeded cover crop in western Nebraska and the ability of a spring seeded cover crop to suppress weeds are currently unknown.
In 2022, 2023, and 2024, field trials were conducted to evaluate if cover crops could be established in the spring and if cover crops would reduce Palmer populations. Spring wheat was planted in mid-March at 100 pounds per acre in all three years and removed at dry bean planting. Results from 2022 are poor due to complications from drought. However, a March planted cover crop reduced herbicide-resistant Palmer amaranth density by 50% and 60% in 2023 and 2024, respectively, and doubled crop yield both years; all with the use of standard grower herbicide practices.
“Cover crops should be encouraged for most dry bean growers using overhead irrigation for management of herbicide-resistant weeds,” Lawrence said.