Non Technical Summary
This is an Applied Research (ARDP, single-function) multi-state project that contributes to CPPM focus area 1 - Plant Protection Tactics and Tools. Stakeholders from across Midwest, South, and Central Great Plains of the U.S. have identified pigweeds (Palmer amaranth and waterhemp) as one of the most problematic and economically damaging weed species. Both pigweeds currently pose a serious threat to sustainable crop production due to a limited effective herbicide options. Widespread multiple resistance to 6-7 different herbicide sites-of-action has increased the need and the desire for IPM-based solutions for managing pigweeds in soybean-based cropping systems of the U.S. For this stakeholder-identified research, we propose to: 1) evaluate the effectiveness of two ecologically-based tactics, namely cover crop and harvest weed seed control (chaff lining and weed seed destructor), within an integrated weed management (IWM) framework, for managing pigweed seed banks in soybean, and 2) quantify the economic benefits and risks of adopting a diversified IWM program to mitigate herbicide resistance. We will conduct multi-location (IA, AR, and KS) field and greenhouse/laboratory studies to develop and integrate these ecological tactics that have a high likelihood of reducing pigweed seed banks and exposure of this species to herbicides, thereby reducing selection for herbicide resistance evolution across the three major soybean production regions. Implementation and adoption of these ecologically-based IWM strategies will reduce potential environmental impacts and applicator exposure problems associated with increased pesticide use. Results from this IWM project will be disseminated across geographic boundaries to meet the National IPM Roadmap Goals.
Animal Health Component
Research Effort Categories
Goals / Objectives
The main goal of this applied research (ARDP, single function) is to integrate two innovative IPM tactics, namely, cover crop and HWSC (chaff lining and seed destructor), within an integrated weed management (IWM) framework, for managing pigweed (Palmer amaranth and waterhemp) seedbanks in soybean-based rotations within the Midwest, South, and Central Great Plains, with a long-term aim of developing resilient weed management systems with reduced economic and environmental risks from HR pigweeds. In order to accomplish our long-term goals, we propose the following Specific Objectives (SO) for this applied research project:Integrate ecologically-based IWM strategies, namely, cover crop and chaff lining/seed destructor (HWSC), for managing pigweed seed banks in soybeanField and laboratory/greenhouse studies to determine the impact of cereal rye cover crop, chaff lining and seed destructor (HWSC) on Palmer amaranth and waterhemp seed bank dynamics (germination/emergence pattern/periodicity, density, seed viability), crop-weed competition (growth, biomass), control, and end-season seedbank inputs.Evaluate the efficacy of chaff lining (HWSC) as a novel, cost-effective IPM tactic (interaction with cereal rye cover crop and herbicides) on fate of pigweed seeds and to reduce spread of HR pigweed seeds.Evaluate the efficacy of seed destructor as a novel, IPM tactic (interaction with cereal rye cover crop and herbicides) to destroy (kill) Palmer amaranth and waterhemp seeds and reduce soil weed seed banks.On-field assessments of how regional weather variables across three major U.S. soybean production regions (Iowa, Kansas, and Arkansas) interact with IWM practices (cereal rye cover crop by herbicide by HWSC methods) at a system level to mitigate risk of weed resistance evolution.Quantify the economic benefits and risks of adopting a diversified IWM program to mitigate herbicide resistance for development of decision support tools (DSTs) for producers and other stakeholders.
Objective 1: Field experiments will be initiated at University Research Farms in Ames, Iowa; Keiser, Arkansas; and on a grower's field near Great Bend, Kansas in the fall of 2021. Experiments at each location will be conducted over two cropping cycles of soybean (2022 and 2023) to quantify the effect of "many little hammers (cover crop, herbicides, and HWSC methods)' on the HR pigweed seed bank. A final evaluation on overall reduction in pigweed seed bank will be conducted in the spring/summer of 2024. The Iowa field site will have a natural uniform infestation of glyphosate-resistant waterhemp (predominant pigweed in the region), and the Arkansas and Kansas sites will have a natural uniform infestation of glyphosate-resistant Palmer amaranth (predominant pigweed in the region). A strip-split-plot randomized complete block design with four replications will be established. The first cropping cycle of the study will be conducted in 2021-2022 in soybean and the second in 2022-2023 in soybean. Soybean yields and all inputs (seed, fertilizer, fuel, labor, equipment cost etc.) will be measured and recorded for use in the economic analysis (Objective 2). Strip plot factor (2 levels): It will include cover crop vs. no cover crop. The cereal rye cover crop will be terminated 0 to 14 days prior to soybean planting depending on locally-adopted cover crop termination practices and soybean planting timings (early to mid-May). No cover crop plots will be kept fallow (no-till) until soybean planting. Whole plot factor (3 levels): The whole plot will include 3 different herbicide programs, initiated at the time of cover crop termination in spring 2022 and 2023. Herbicide programs include: (1) one-pass approach of cereal rye termination with glyphosate plus soil-residual PRE (flumioxazin + pyroxasulfone; Fierce®), (2) a two-pass approach of cereal rye termination with glyphosate plus the soil-residual PRE followed by a POST glufosinate, (3) cover crop termination with glyphosate only (weedy check) in a glyphosate- and glufosinate-tolerant soybean. Split plot factor (3 levels): This will include: (1) no HWSC, (2) chaff lining, and (3) seed destructor. These treatments will be implemented at soybean harvest in fall 2022 and repeated in fall 2023. Pigweed seed retention and header loss of weed seeds at te time of soybean harvest will be determined using our established protocol. Chaff lining (Objective 1b): At each location in the fall of 2022 and 2023, we will use a custom-designed chaff liner installed to the rear of a commercial combine with an 11-m wide header. We expect to see different soybean yield scenarios across locations, which will have a direct relationship with the amount of soybean chaff collected and subsequent weed control (suppression of emergence). The chaff liner will include a baffle to separate the soybean chaff from the straw and a chute to divert the weed seed-bearing chaff fraction (from the sieves) into a narrow windrow (45-50 cm wide by 15-20 cm deep). The chaff material exiting through the chaff liner chute will be collected as the rear of the combine passes over the trays in the field. Any pigweed seeds lost in the straw fraction (thresher loss) exiting through the straw chopper will be captured behind the combine. Samples will also be collected from No HWSC plots for comparison. Pigweed seeds will be separated from the chaff material or straw and counted (seeds. m-2). The effect of chaff lining on pigweed seed viability (survival) will be quantified. Weed Seed Destructor (Objective 1c): Redekop® Seed Destructor units integrated with commercial combines will be used. The efficacy of the seed destructor will be determined by collecting the chaff material (containing weed seeds that passed through the high-impact mill). Waterhemp seeds retained in the straw fraction (thresher loss) will be captured behind the straw chopper of the combine (seed destructor and no HWSC plots). Palmer amaranth/waterhemp seed will be separated from the soybean chaff/straw material and counted (no. m-2). The weed seed kill efficacy of the seed destructor and effect on emergence of pigweeds in each plot will be determined. The second cycle of the study (year 2) will initiate with cereal rye cover crop planting in fall 2022 followed by soybean planting in spring 2023 and implementation of HWSC treatments in fall 2023 on the existing plots (year 1) in the field at all three locations. This will allow us to determine the effect of HWSC treatments on pigweed population dynamics in the subsequent soybean crop in addition to understanding the cereal rye cover crop by herbicide by HWSC interactions (Objective 1d). The study will be terminated in fall 2023 with the implementation of HWSC treatments at soybean harvest. A final assessment of the cumulative effect of this IWM approach on HR pigweed seed bank reduction will be conducted in spring/summer 2024.Data Collection: Cereal rye growth stage, height, and aboveground shoot biomass from four 0.5 m2 quadrats in each split plot will be sampled just prior to the cover crop termination each year. Additionally, cover crop residue samples from two 0.25 m2 per plot will be taken at V3-V4 stage of the soybean (POST timing), soybean canopy closure (late-season), and at harvest. Four permanent 0.5 m2 quadrats will be established in each split plot. Pigweed emerging in each quadrat will be marked separately to establish three different emergence cohorts (planting through V3 stage, V3 to V6 stage, and after V6 through R2 soybean stage). Data on pigweed emergence period (beginning and end dates), emergence counts, and plant height will be monitored from those 0.5 m2 quadrats at biweekly intervals and a final assessment of pigweed density at soybean harvest. Visual estimates of weed control will also be evaluated at 3 weeks after herbicide treatment, and again prior to soybean harvest. At harvest, pigweed density, biomass, and seed production (by cohort) will be measured in the four 0.5 m2 quadrats in each plot. Soybean grain yield will be determined. To quantify the effect of chaff lining on the pigweed seed survival, seeds will be separated from the soil (seed packets inside vs. outside chaff lines) and incubated (petri dish assay) at 25 C in the laboratory for 4 weeks (Steckel et al. 2004). For the samples collected from the seed destructor plots, percent seed destruction by the high-impact mill will be destermined. Seeds will be germinated at 25 C (optimum temperature) for 4 weeks in an incubator and any non-germinated seed will be tested for viability using a standard crush test (Sawma and Mohler 2002). Seed samples from No HWSC plots will be used for comparison to determine the efficacy of the seed destructor in reducing pigweed seed viability and percent germination. With the conclusion of two cycles (year 1 and year 2) of the study, cumulative effect of cereal rye cover crop by herbicide by HWSC on pigweed seedbank will be assessed using an exhaustive germination method in the greenhouse from soil samples collected from each split plot in early spring of 2024. Final assessments of pigweed emergence in the permanent four 0.5 m2 quadrats in each split plot will also be conducted at biweekly intervals in 2024 spring/summer as well as viability assessment of the seed packets from fall 2023 chaff line treatments, prior to terminating the study. Objective 2: Economic and Resistance Risk Assessment Model: A model similar to that proposed by Neve et al. (2011a; 2011b) will be used to calculate the resistance risk from the two ecological/non-chemical IPM practices, namely cover crop and HWSC (chaff lining and seed destructor) combinations, under different levels of herbicide selection pressure. Our model will also complement the existing Palmer Amaranth Management (PAM) decision support tool (DST). The PAM model can then be expanded to include IWM tactics (cover crop, chaff lining, and seed destructor- HWSC methods).