Progress 04/01/24 to 03/31/25

Outputs
Target Audience:1. Organic crop production researchers and weed scientists who are looking for alternative methods for nonchemical weed control as it pertains to using microwave to kill weed seeds. 2. Colleagues and private agriculture machinery enterprise from Brazil who want to collaborate on developing a field prototype for microwave application. 3. Those who are in the professional weed science society circle - as it pertains to late-season weed control to reduce weed seed deposit. Changes/Problems:One change that we had to make was to conduct separate experiments to evaluate the cotton response from the weed response. In the proposal, cotton was to be planted in a field infested with various key weeds. It became apparent that conducting the test like this would compromise our ability to evaluate the treatment effects well. Therefore, in 2024, we conducted four weed tests without cotton (grass - early timing, grass late- timing, broadleaf - early timing, and broadleaf - late timing). This turned out to be a better approach. In 2025, the weed tests will be repeated and the cotton response tests will be conducted in a field maintained free of weeds. What opportunities for training and professional development has the project provided?The post-doctoral associate and graduate students attended professional conferences and presented posters of preliminary data. These personnel were trained on how to collect soil samples for this research, prepare samples for MW treatment, how to implement the treatments, and how to conduct seed germination test in the greenhouse. Personnel were also trained on how to identify the weed species present. During the process of planning the experiments and data analysis, research personnel were trained on experimental design and data analysis as it applies to this experiment. How have the results been disseminated to communities of interest?Preliminary results were shared to potential collaborators and current producer collaborators to strengthen awareness and encourage continued support for this project. What do you plan to do during the next reporting period to accomplish the goals?1.Objective 1: Repeat the field experiments on grass and broadleaf weeds. Evaluate seed production and conduct seed germination tests. In the fall, conduct the first batch of greenhouse experiment to evaluate the effect of herbicide x TE treatments on key weeds that did not establish at sufficient levels in the field. Among these are: barnyardgrass, large crabgrass, broadleaf signalgrass, hemp sesbania, common ragweed, and pale smartweed. This series of greenhouse experiments will start with hemp sesbania in the fall 2025. Two field experiments will be conducted on weed-free cotton to evaluate TE x herbicide combinations at two growth stages: 4-leaf and close to layby. 2. Objective 2: The first batch of soil adjuvant x residual herbicidetest will be conducted in the greenhouse in the fall 2025 using Palmer amaranth as bioassay species. 3. Objective 3: Microwave treatments will be evaluated on other target weed species, grass and broadleaf, representing different seed sizes and hardness of seed coat.

Impacts
What was accomplished under these goals? Objective 1:Assess the effect of trinexapac-ehtyl (TE) on the efficacy of multiple herbicides on yellow foxtail (YF, Setaria pumila), broadleaf signalgrass (BS, Brachiaria platyphylla), southwestern cupgrass (SC, Eriochloa acuminata) and barnyardgrass (BG, Echinochloa crus-galli). A field study was conducted in 2024 at SAREC, University of Arkansas, where grass species were sown in 120 ft2 plots. This experiment followed a split plot-design with four replications. The treatments included TE (0, 0.534 lb/A) in mixture with the following herbicides: glyphosate (0.5, 0.65 lb/A), glufosinate-ammonium (0.32, 0.64 lb/A), flumioxazin (0.031, 0.062 lb/A), topramezone (0.009, 0.018 lb/A), clethodim (0.125,0.25 lb/A), quizalofop (0.031, 0.063 lb/A) and prometryn (0.8,1.6 lb/A). Herbicides were sprayed at 12-inch weeds (Study 1) and near-reproductive stage (Study 2). Visible control (%) was evaluated at to 21 d after treatment (DAT). Optimum differentiation of treatments was obsereved at 21 DAT, TE did not increase the efficacy of clethodim. Glufosinate-ammonium and glyphosate controlled all species 100% at the rates used. Prometryn controlled grass species 5-25% without TE. The efficacy of prometryn on BG and FT increased by 30% points with the addition of TE and increased by 40-50% points on SC and BS. TE also increased the activity of quizalofop by 20-30% points on BG, YF, and SC and 15% points on BS. Grass control with topramezone increased 35-35% for BY, YF and SC and 40-50% for BS. the mixture of TE with flumioxazin was synergistic, showing 50 - 60% improved in control of all species 21 DAT. While only glyphosate and glufosinate had 100% grass control, the increased control levels with TE mixture would likely reduce seed input into the seedbank. These results suggest that trinexapac-ethyl improves the activity of flumioxazin, topramezone, quizalofop, and prometryn on grass weeds. Further studies will evaluate the profitability of these mixtures. Twnety-eight TE x herbicide combinations were also tested on braodleaf weed species. These included Palmer amaranth, velvetleaf, prickly sida, and hemp sesbania. Weeds were harvested from up to 10 plants per plot for Palmer amaranth and velvetleaf. The other two species did not have reproductive plants in the majority of plots. Seed germination tests are on-going. Objective 2. Evaluation of the interaction of soil conditioners with residual herbicides. This experiment will be conducted as soon as activities for objective 1 wind down. Objective 3. Evaluation of microwave energy to kill weed seeds. Soil sampling.Silt loam and clay loam soil were collected from the University of Arkansas Division of AgricultureVegetable Research Station at Kibler, AR and from a rice/cotton field in Marion, AR, respectively. The soil samples were placed in sealed containers, then conditioned to approximately 20-25% soil moisture content (wet basis) to mimic soil moisture in crop fields before sowing. Microwave treatment.The industrial MW dryer (Model No. AMT2448.05, Industrial Microwave Systems, AMTEK, Cedar Rapids, IA) was used. The unit was operated at a 915 MHz frequency and consisted of 75 kW generator, 48-inch (121.9 cm) length drying oven, and a console for its operation. Soil to be treated was transferred to a polypropylene tray and a 4 in by 8 in a desired soil depth before treatment. Before each treatment, 25 seeds of junglerice weed were placed uniformly on 0.5 in of soil before piling up to the 3-in (7.6 cm) of soil depth. The initial seed germination of junglerice was 88%. Soil surface temperature was measured immediately after microwave treatment. After treatment, soil was mixed using a spatula, allowed to cool for 2 min, placed in plastic bags, then placed in trays in the greenhouse to evaluate germination. Experimental design. Seven levels of microwave treatment (factor #1) were tested with 6 factorial combinations of 3 power levels and 2 treatment durations. Control sample with no microwave treatment was the the 7th treatment. Two soil types (factor #2), silt loam and clay loam were included in the experiments. Soil depth was fixed to 3 in (7.6 cm). Seed germination assay in the greenhouse. The treated and nontreated soil samples were placed in 2-inch-deep containers with drainage holes at the bottom. The soil in containers was soaked in water to full saturation and then drained to 'field water holding capacity'. Weed emergence was assessed over three weeks (21 days). Emerged weeds were counted on day 7, 14 and 21; seedlings were removed after each count and the soil in each container was thoroughly mixed on day 7 and 14 to facilitate germination of all viable, non-dormant seeds. All emerged species were identified visually and counted as germinated. After the final count of germination, the total number of germinated seeds was normalized to account for the variability in initial level of infestation in soil samples. This is because the field soil is expected to have some natural infestation of junglerice. The level of seedling emergence was compared by calculating the total germinability index (TGI) Data Analyses.Data were subjected to analysis of variance (ANOVA) using JMP Pro 18 statistical software (JMP Pro 18, SAS Institute, Cary, NC) using a 4-factor factorialcompletely randomization design. The normality of data and homogeneity of variance were examined. The ANOVA was conducted to test the effect of microwave treatment, depth of seed placement and soil type and their interactions on the total germinability index and soil surface temperature. Student's t-test was used to compare the levels of each factor at at a 95% confidence level. Results: The effect of microwave treatment on TGI and soil surface temperature (SST) was significant but soil type and the interaction of these factors were not significant. The microwave treatment 10 kW for 30 sec raised the SST of silt loam soil by around 60 C - 70 C relative to the nontreated.The heating of soil surface with the lowest microwave energy level approached that of higher-energy treatments when the duration of exposure was extended to 60 sec.The treatment using any power levels for 60 sec consistently demonstrated the lowest TGI significantly reduced weed seed germination compared to the other microwave treatment levels. This suggests that longer exposures even at lowest power level are more effective at inhibiting weed seed germination. The control group, which did not receive any microwave treatment, had the highest TGI. The soil type did not significantly alter the outcomes, indicating a broad applicability of this method across different soil conditions. Furthermore, the interaction between microwave treatment and soil type showed no significant impact on TGI and SST, underscoring the consistency of microwave treatment effectiveness irrespective of soil variance.

Publications