Recipient Organization
LOUISIANA STATE UNIVERSITY
202 HIMES HALL
BATON ROUGE,LA 70803-0100
Performing Department
(N/A)
Non Technical Summary
Growers from across the U.S. have identified the need to develop novel, alternative integrated weed management (IWM) systems to mange pigweeds (Palmer amaranth and waterhemp) with multiple resistance to 6-9different herbicide modes of action.Both pigweeds currently pose a serious threat to sustainable crop production in theU.S. due to a limited effective herbicide options.The multiple herbicide-resistance (6- to 9-way resistance) in Palmer amaranthand/or waterhemp has caused severe yield losses in the two major U.S. crops, corn and soybean, and also increasedproduction costs. A lack of new commercialized herbicide sites-of-action (SOA) and increased relianceon herbicide mixtures havegreater environmental impacts and threat of weedpopulations with multiple resistance. The annualimpact of herbicide-resistant (HR) weeds on growers is estimated at over $2 billion and has continued to increase as theproblem spreads, especially for these two pigweed species in the U.S.For this stakeholder-identified research, we propose to: 1) evaluatethe effectiveness of two nonchemical tactics, namely cover crop and harvest weed seed control (chaff lining), in conjuction with herbicides with multiple moders of action, for managing pigweed seed banks in soybean, and 2) quantify the economicbenefits and risks of adopting a diversified IWM program to mitigate herbicide resistance. Harvest weed seed control method ofchaff lining in soybean concentrates weed seed-bearing crop and weed chaff into a narrow row (chaff line). These chaff lines (30- to 50-cm wide) are undisturbed the following growing seasons, under the assumption that the chaff line creates an environment less favorable for weed seed germination and survival. The first research on chaff lining in soybeanconducted in the U.S. by the PDs indicated more than 95% reduction in the spread of glyphosate-resistant waterhemp seeds at the time of soybean harvest and significant reductions in overall herbicide use in a two-year soybean-corn rotation in Iowa. We will conduct multi-location field and greenhouse/laboratory studies to develop andintegrate these novel tactics that have a high likelihood of reducing pigweed seed banks and exposure of this species toherbicides, thereby reducing selection for herbicide resistance evolution across the major soybean production regions ofthe U.S (Louisiana, Arkansas, Illinois, and New York).Implementation and adoption of these ecologically-based IWM strategies will reduce potential environmental impactsand applicator exposure problems associated with increased pesticide use. It would also aid in mitigating negative effects on soil healthas farmers have revertedback to tillage to control pigweeds on their farm fields. Apart from conventional systems, chaff lining in conjunction with cover crops can be utilized as a novel IPM tactic to manage weeds in organic soybean production systems.
Animal Health Component
90%
Research Effort Categories
Basic
0%
Applied
90%
Developmental
10%
Goals / Objectives
The main goal of this applied research (ARDP, single function PD transfer project) is to integrate two innovative IWM tactics, namely, covercrop and HWSC (chaff lining), within an integrated weed management (IWM) framework, for managing pigweed (Palmeramaranth and waterhemp) seedbanks in soybean-based cropping systems of the Southern, Midwestern, and other Northern states in the U.S., with a long-term aim of developing resilient weed management systems with reduced economic andenvironmental risks from HR pigweeds.In order to accomplish our long-term goals, we propose the following Specific Objectives (SO) for this applied research project:1. Integrate ecologically-based IWM strategies, namely, cover crop and chaff lining (HWSC), for managing pigweedseed banks in soybean.1.1. Field and laboratory studies to determine the impact of cereal rye cover crop, chaff lining (HWSC) on Palmer amaranthand waterhemp seed bank dynamics (germination/emergence pattern/periodicity, density, seed viability, seed predation), crop-weedcompetition (growth, biomass), control, and end-season seedbank inputs.1.2. Evaluate the efficacy of chaff lining (HWSC) as a novel, cost-effective IWM tactic in reducing HR pigweed seed banks,with emphasis on:. a. Percent seed retention at soybean harvest;b. Header loss of pigweed seeds at soybean harvest;c. Efficacy of chaff lining to concentrate pigweed seeds in narrow bands and prevent spread of HR weed seeds2. On-field assessments of how regional weather variables across four major U.S. soybean production states (Louisiana,Arkansas, Illinois, and New York) interact with IWM practices (cereal rye cover crop by herbicide by chaff lining) at a system levelto mitigate risk of weed resistance evolution.3. Quantify the economic benefits and risks of adopting a diversified IWM program to mitigate herbicide resistancefor development of decision support tools (DSTs) for producers and other stakeholders.
Project Methods
Objective 1: Field experiments for two years were completed at the Arkansas and Illinois locations in 2022-2024. Experiments will be established at the University Research Farms in Louisiana and New York in 2026 and 2027. Field sites will have a natural uniforminfestation of glyphosate-resistant waterhemp/Palmer amaranth. Experimentswill be conducted in two different soybean fields in fall 2025-fall 2026(run 1) and in fall 2026-fall 2027(run 2) in a soybean-soybeanrotation at each stateto quantify the effect of "many little hammers" (cover crop, herbicides, and HWSC method of chaff lining) on HR pigweedseed banks. A randomized complete block design with a factorial arrangement of treatments (12 total) and fourreplications will be used.Chaff lining (Factor 1): It will include chaff lining vs. no chaff lining (conventional harvest). The chaff lining treatment at eachsite will be implemented at the time of soybean harvest in the fall of 2025(run 1) and fall of 2026(run 2). Each plot will be 10-m wide by 30-m long. At each site, we will use a custom-designed chaff liner installed at the rear of a commercial combine witha 9-m wide header. The chaff liner will include a baffle to separate the soybean chaff from the straw and a chute to divert theweed seed-bearing chaff fraction (from the sieves) into a narrow windrow (45-50 cm wide by 15-20 cm deep), while the strawfraction will be chopped and spread out in the field at soybean harvest. The chaff material exiting through the chaff liner chutewill be collected by placing three aluminum trays (25 by 38 cm) per plot as the rear of the combine passes over the trays in thefield. Any pigweed seeds lost in the straw fraction (thresher loss) exiting through the straw chopper will be captured on a tarpthat unrolls behind the combine. Samples will also be collected from No chaff lining plots for comparison. Pigweed seeds will beseparated from the chaff material or straw and counted (seeds. m-2).Cover crop (Factor 2): It will include: cover crop vs. no cover crop. The cereal rye cover crop will be terminated 0 to 14 daysprior to soybean planting depending on locally-adopted cover crop termination practices and soybean planting timings (early tomid-May), with the ultimate goal to obtain at least 5,000 kg ha-1 of cereal rye biomass at the time of termination. No cover cropplots will be kept fallow until soybean planting in 2026 and 2027.Herbicide programs (Factor 3): Three different herbicide programs, initiated at the time of cover crop termination in the springof 2026(run 1) and 2027(run 2) will be investigated. Herbicide programs include: (1) cover crop termination with glyphosate +2,4-D (weedy check), (2) a one-pass approach of cover crop termination with glyphosate + 2,4-D plus a soil-residual PRE(pyroxasulfone; Zidua SC®), and (3) a two-pass approach of cover crop termination with glyphosate + 2,4-D plus soil-residualPRE (flumioxazin + pyroxasulfone; Fierce EZ®) followed by a POST [glufosinate, Liberty™ + 2,4-D, Enlist One™] treatment insoybean (Enlist, E3 beans with tolerance to glyphosate, glufosinate, and 2,4-D choline).Data Collection: Cereal rye growth stage (in feekes), height, and aboveground shoot biomass from four 0.5 m2 quadrats ineach plot will be sampled just prior to the cover crop termination. To monitor pigweed emergence, eight permanent 0.5 m2quadrats (four each in the chaff line and non-chaff line areas of a plot) will be established to monitor pigweed emergence in thesubsequent soybean crop at biweekly intervals. Data on pigweed emergence period (beginning and end dates), emergencecounts, and plant height will be monitored from those 0.5 m2 quadrats at biweekly intervals and a final assessment of pigweeddensity at soybean harvest. Visual estimates of weed control will also be evaluated at 3 weeks after herbicide treatment, andagain prior to soybean harvest. At harvest, pigweed density, biomass, and seed production (by cohort) will be measured in theeight 0.5 m2 quadrats in each plot. Weed biomass and seed production will be estimated. Soybean grain yield will bedetermined.To quantify effects on pigweed seed viability (Objective 1a, b), seed packets made with nylon mesh bags will be filled withequal amounts of seed mixed with soil (to reduce the potential for mold) based upon waterhemp/Palmer amaranth seed massusing 1000-seed count estimates for local seed at each field site immediately after soybean harvest. Ten seed packets per plotwill be placed either underneath the chaff or on top of the bare soil (no chaff area of the plot) in chaff lining treatments, or on soilsurface in no chaff lining plots. Two seed packets per plot will be collected at each of the five timings: overwinter, at cover croptermination (PRE timing), V3-V4 stage of the soybean (POST timing), soybean canopy closure (late-season), and at harvest.Seeds will be separated from the soil and incubated (petri dish assay) at 25 C in the laboratory for 4 weeks. Imbibed germinatedseeds (viable) will be counted and removed. Any nongerminated seed will be subjected to a standard crush test for assessingviability.To quantify losses in the pigweed seed bank due to seed predation (Objective 1a, b), a pitfall trap will be placed between rowsof soybean stubble in a central location in each experimental plot, either beneath the chaff in plots vs. outside the chaff line inplots receiving the chaff line treatment, or in the open in other treatment (no chaff lining, conventional harvest). Throughout theobservation period (fall through subsequent growing season), arthropods caught in all traps will be collected every 3-4 days, orca. 24 h after any rain event, and the propylene glycol replaced, as needed. Subsequent identification of insect specimens togenus or species level.Statistical Analysis: A mixed-model ANOVA will be used, considering block (within site) and site and associated interactionsas random effects. Chaff lining, cover crop, herbicides, and all interactions among these three factors will be fixed effects.Response variables will include percent pigweed seed retention at soybean harvest, chaff lining efficacy (% of pigweed seedsconcentrated in chaff line vs. outside chaff line in a plot), pigweed species emergence count, density, biomass, control, seedproduction, and crop yield (field measurements), pigweed seed viability percent (seed packets; laboratory experiment), andseed predation.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 andHWSC (chaff lining) combinations, under different levels of herbicide selection pressure. Our model will also complement theexisting Palmer Amaranth Management (PAM) decision support tool (DST) developed by the University of Arkansas(Norsworthy lab) which uses population dynamics modeling, efficacy of weed management approaches, and economics to allowcomparison of management strategies though seedbank, crop yield, net returns and herbicide risk assessment. The PAM modelcan then be expanded to include IWM tactics (cover crop and chaff lining method of harvest weed seed control).