Integrated weed management strategies in cover crop-based, organic rotational no-till corn and soybean in the mid-Atlantic region

Authors: WALLACE, JOHN - Pennsylvania State University; KEENE, CLAIR - North Dakota State University; CURRAN, WILLIAM - Pennsylvania State University; Mirsky, Steven; RYAN, MATTHEW - Cornell University; VAN GESSEL, MARK - University Of Delaware

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2018
Publication Date: 1/1/2018
Citation: Wallace, J.M., Keene, C.L., Curran, W.S., Mirsky, S.B., Ryan, M.R., Van Gessel, M.J. 2018. Integrated weed management strategies in cover crop-based, organic rotational no-till corn and soybean in the mid-Atlantic region. Weed Science. 66:94-108.

Interpretive Summary: Farmers growing organic corn and soybeans in the mid-Atlantic region are experimenting with the combined practices of cover crop use and no-till to make their cropping systems profitable and sustainable. These systems are referred to as cover crop-based, organic rotational no-till (CCORNT) systems. These systems cannot rely on herbicides for weed control (because there are no truly effective, economically-feasible herbicides listed for use in organic systems), and choose not to rely on tillage for weed control (because tillage has a severely detrimental effect on soil structure and health). As a result, CCORNT systems rely on a multi-tactic weed control approach in corn and soybeans that includes managing cover crop residue to best suppress weeds, plus the use of a high residue (HR) cultivator that can control weeds without disturbing the soil. A cropping system experiment was conducted in Pennsylvania, Maryland, and Delaware to test the cumulative effects of a multi-tactic weed management approach in a 3-yr hairy vetch/triticale – corn – cereal rye – soybean – winter wheat CCORNT rotation. The multi-tactic weed management treatments included differing cover crop termination dates (early, middle, and late; to test the effect of differing cover crop biomass residue levels on weeds), differing cash crop planting dates (early, middle, and late; the soil disturbance caused by cash crop planting can induce weed germination, but some weeds only germinate during specific time periods each year and as such can be “waited out”), and supplemental weed control using high-residue (HR) cultivation in no-till corn and soybean phases. To specifically test the effect of cash crop planting timing on weeds, plots were seeded with species known to vary in emergence periodicity (common ragweed, giant foxtail, and smooth pigweed) to ensure that a known number of test subjects (i.e., potential weeds) were present. In the no-till corn phase, HR cultivation decreased weed biomass relative to the uncultivated controls by 23-62%. In the no-till soybean phase, HR cultivation decreased weed biomass by 20-78% relative to uncultivated soybean planted in narrower rows (38 cm). Cash crop phase and planting date timing influenced weed biomass and density composition. Common ragweed produced more biomass than other weeds in soybean (39% of total weed biomass) than corn (10%), while giant foxtail and smooth pigweed produced more biomass than other weeds in corn, comprising 46 and 22% of total biomass, respectively. Across summer annual cash crops, common ragweed became less abundant as planting dates were delayed, while giant foxtail and smooth pigweed increased as a percentage of total biomass. At the Pennsylvania location, cover crops were not realiably successfully terminated, resulting in volunteer (weedy) cover crops in other phases of the rotation. Our results indicate that HR cultivation is likely necessary to achieve adequate weed control in CCORNT systems. Cover crop residue alone is not sufficient to control weeds. The inclusion of winter grain or perennial forages into CCORNT systems is also an important weed management tactic for decreasing the weed seedbank following no-till corn and soybean phases because winter grains and perennial forages require different management that presents further opportunities for weed control. This information will be useful to scientists developing CCORNT systems.

Technical Abstract: Cover crop-based, organic rotational no-till (CCORNT) corn and soybean systems have been developed in the mid-Atlantic region to build soil health, increase management flexibility, and reduce labor. In this system, a roll-crimped cover crop mulch provides within-season weed suppression in no-till corn or soybean. A full-entry cropping system experiment was conducted in Pennsylvania, Maryland, and Delaware to test the cumulative effects of a multi-tactic weed management approach in a 3-yr hairy vetch/triticale – corn – cereal rye – soybean – winter wheat CCORNT rotation. The multi-tactic weed management treatments included cover crop termination/cash crop planting dates (early, middle, late), and supplemental weed control using high-residue (HR) cultivation in no-till corn and soybean phases. Weed management treatments were imposed in split-split-plots in the no-till corn and soybean phases of the rotation. Supplemented weed seedbanks comprised of common ragweed, giant foxtail, and smooth pigweed were used to quantify the effects of the weed management tactics on summer annual weed species that vary in emergence periodicity. In the no-till corn phase, HR cultivation resulted in an average 58, 23, and 62% decrease in weed biomass relative to the uncultivated controls in Delaware, Maryland, and Pennsylvania, respectively. In the no-till soybean phase, HR cultivation resulted in an average 20, 41, and 78% decrease in biomass relative to uncultivated soybean planted in narrower rows (38 cm) in Delaware, Maryland, and Pennsylvania, respectively. Cash crop phase and planting date timing influenced weed biomass and density composition. Common ragweed was more dominant in soybean (39%) than corn (10%), whereas giant foxtail and smooth pigweed were more dominant in corn, comprising 46 and 22% of total biomass, respectively. Across summer annual cash crops, common ragweed became less abundant as planting dates were delayed, while giant foxtail and smooth pigweed increased as a percentage of total biomass. At the Pennsylvania location, inconsistent termination of cover crops with the roller-crimper resulted in volunteer cover crops in other phases of the rotation. Our results indicate that HR cultivation is likely necessary to achieve adequate weed control in CCORNT systems. Integration of winter grain or perennial forages into CCORNT systems is also an important weed management tactic for truncating weed seedbank population increases following no-till corn and soybean phases.