@article{leon_oreja_mirsky_reberg-horton_2023, title={Addressing biases in replacement series: the importance of reference density selection for interpretation of competition outcomes}, volume={10}, ISSN={["1550-2759"]}, url={https://doi.org/10.1017/wsc.2023.53}, DOI={10.1017/wsc.2023.53}, abstractNote={Abstract Replacement series are used by researchers to understand how competition-related variables influence dynamics from the individual to the population and community levels, but this approach has been criticized because of inherent biases associated with plant size differences and density-dependent responses. The use of functional densities instead of demographic densities was proposed to minimize those biases. This work explored three models to determine reference densities for replacement series experiments based on (1) maximum biomass, (2) biomass at onset of diminishing returns (i.e., inflection point), and (3) nitrogen (N)-uptake equivalency. Replacement series experiments were conducted using redroot pigweed (Amaranthus hybridus L.):maize (Zea mays L.) and giant foxtail (Setaria faberi Herrm.): maize proportions of 1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75, and 0:1. The monoculture density for each species was established according to the three models. Density selection criteria resulted in major differences in competitive interactions between species. The use of functional densities at which the biomass accumulation inflection point for the smaller species allowed both species to exhibit either increases or decreases in biomass production depending on competitive interactions for all interspecific mixtures. Conversely, the maximum biomass model favored the larger species, almost completely inhibiting the growth of the smaller species, which resulted in a poor characterization of competitive responses of the smaller species. The N uptake equivalency model resulted in interactions closer to the predicted neutral competition. The model based on the biomass accumulation inflection point was the most sensitive and informative across all interspecific mixtures for both species. We propose that to reduce bias associated with species size differences when determining reference densities for replacement series experiments, at least two criteria must be met: (1) the experiment sensitivity allows measuring and quantifying the competitive responses for both species in all mixtures, and (2) the balance between density and carrying capacity of the system minimizes intraspecific competition.}, journal={WEED SCIENCE}, author={Leon, Ramon G. and Oreja, Fernando H. and Mirsky, Steven B. and Reberg-Horton, Chris}, year={2023}, month={Oct} }
 @article{mahoney_jordan_leon_oreja_roma-burgos_2023, title={Fecundity and maternal effects on Palmer amaranth height following season-long interference in corn, cotton, and peanut}, volume={9}, ISSN={["2374-3832"]}, url={https://doi.org/10.1002/cft2.20233}, DOI={10.1002/cft2.20233}, abstractNote={Abstract Palmer amaranth ( Amaranthus palmeri Watson) is one of the most difficult‐to‐control weeds in several economically important crops in the United States. Growth characteristics of Palmer amaranth can be affected by the cropping system. Research was conducted in North Carolina in 2019 to determine height and seed production of Palmer amaranth grown season long in the presence of corn ( Zea mays L.), cotton ( Gossypium hirsutum L.), and peanut ( Arachis hypogaea L.). Research was also conducted to determine transgenerational effects due to interference from these crops. Palmer amaranth produced more seed when grown with cotton (17 times greater) and peanut (12 times greater) compared with corn; no difference was noted between cotton and peanut. Palmer amaranth height in the field at physiological maturity was similar in corn (80 inches) and cotton (77 inches) and taller in height than peanut (63 inches). When progeny from plants in the field were grown in the greenhouse in the absence of crop interference, differences in the height of progeny and height of the mother plant in the presence of crop interference were ranked similarly with respect to crop. Palmer amaranth height in the presence of corn and cotton was similar (57 and 58 inches, respectively) and it exceeded height when the weed was grown with peanut (51 inches). These results demonstrate transgenerational effects due to previous crop (e.g., corn, cotton, and peanut) for Palmer amaranth.}, number={2}, journal={CROP FORAGE & TURFGRASS MANAGEMENT}, author={Mahoney, Denis J. and Jordan, David L. and Leon, Ramon and Oreja, Fernando H. and Roma-Burgos, Nilda}, year={2023}, month={Dec} }
 @article{oreja_hare_jordan_leon_2023, title={Previous crop and herbicide timing application effects on weed population growth rate}, volume={9}, ISSN={["2374-3832"]}, url={https://doi.org/10.1002/cft2.20232}, DOI={10.1002/cft2.20232}, abstractNote={Abstract A well‐designed crop rotation can create an unstable environment that disrupts weed population growth rates. In combination with effective herbicide programs, growers may maintain weed populations at levels below competitive and economic thresholds. The objectives of the present study were to evaluate how the preceding rotational crop determines the response of weed populations to in‐season postemergence herbicide programs and the weed population density of the following crop season. The first‐year crop treatments were corn ( Zea mays L.), cotton ( Gossypium hirsutum L.), peanut ( Arachis hypogaea L.), grain sorghum [ Sorghum bicolor (L.) Moench.], and soybean [ Glycine max (L.) Merr.]. In the second year, all plots were planted with cotton, and herbicide treatments were single applications 2 or 6 weeks after planting (WAP), two sequential applications 2 and 4 or 4 and 6 WAP, three sequential applications 2, 4, and 6 WAP, and a weedy control without herbicides was included. In the absence of herbicides, corn had the lowest population growth rates for broadleaf weeds (λ = 0.8) while peanut and grain sorghum had the highest (λ = 1.7 and 1.3, respectively). The results indicated that herbicide applications focused exclusively on preventing yield loss may not be sufficient to ensure weed population reductions. Thus, the observed population growth rates (λ = 2 for grassy weeds and λ = 1.26 for broadleaved weeds) indicated that weed issues would continue increasing, despite meeting yield goals. Considering population growth rates when assessing weed management strategies is key to determining the sustainability of the crop production operation.}, number={2}, journal={CROP FORAGE & TURFGRASS MANAGEMENT}, author={Oreja, Fernando H. and Hare, Andrew T. and Jordan, David L. and Leon, Ramon G.}, year={2023}, month={Dec} }
 @article{oreja_inman_jordan_vann_jennings_leon_2022, title={Effect of cotton herbicide programs on weed population trajectories and frequency of glyphosate-resistant Palmer amaranth (Amaranthus palmeri)}, volume={7}, ISSN={["1550-2759"]}, url={https://doi.org/10.1017/wsc.2022.41}, DOI={10.1017/wsc.2022.41}, abstractNote={Abstract The adoption of dicamba-resistant cotton (Gossypium hirsutum L.) cultivars allows using dicamba to reduce weed populations across growing seasons. However, the overuse of this tool risks selecting new herbicide-resistant biotypes. The objectives of this research were to determine the population trajectories of several weed species and track the frequency of glyphosate-resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) over 8 yr in dicamba-resistant cotton. An experiment was established in North Carolina in 2011, and during the first 4 yr, different herbicide programs were applied. These programs included postemergence applications of glyphosate, alone or with dicamba, with or without residual herbicides. During the last 4 yr, all programs received glyphosate plus dicamba. Biennial rotations of postemergence applications of glyphosate only and glyphosate plus dicamba postemergence with and without preemergence herbicides were also included. Sequential applications of glyphosate plus dicamba were applied to the entire test area for the final 4 yr of the study. No herbicide program was entirely successful in controlling the weed community. Weed population trajectories were different according to species and herbicide program, creating all possible outcomes; some increased, others decreased, and others remained stable. Density of resistant A. palmeri increased during the first 4 yr with glyphosate-only programs (up to 11,739 plants m–2) and decreased a 96% during the final 4 yr, when glyphosate plus dicamba was implemented. This species had a strong influence on population levels of other weed species in the community. Goosegrass [Eleusine indica (L.) Gaertn.] was not affected by A. palmeri population levels and even increased its density in some herbicide programs, indicating that not only herbicide resistance but also reproductive rates and competitive dynamics are critical for determining weed population trajectories under intensive herbicide-based control programs. Frequency of glyphosate resistance reached a maximum of 62% after 4 yr, and those levels were maintained until the end of the experiment.}, journal={WEED SCIENCE}, publisher={Cambridge University Press (CUP)}, author={Oreja, Fernando H. and Inman, Matthew D. and Jordan, David L. and Vann, Matthew and Jennings, Katherine M. and Leon, Ramon G.}, year={2022}, month={Jul} }
 @article{oreja_inman_jordan_bardhan_leon_2022, title={Modeling weed community diversity based on species population density dynamics and herbicide use intensity}, volume={138}, ISSN={["1873-7331"]}, DOI={10.1016/j.eja.2022.126533}, abstractNote={Herbicide programs change weed population density as well as weed community composition. The repeated use of a given program can result in a weed community that progressively becomes more difficult to manage or could lose its ability to provide ecosystem services. Simulation of those changes using stochastic models considering population dynamics of multiple species makes it possible to identify a priori potential community changes that might result from the use of a given herbicide program. The objectives of this work were to model the population dynamics of weed species under different herbicide programs and how those dynamics change weed community diversity over time. Weed population dynamics were stochastically modeled along ten years using population growth rate (lambda) for each species under different herbicide programs. Lambda values were obtained from an eight-year long, field experiment, and these were used to parameterize the stochastic ranges for the model for each weed species. Population trajectories were modeled for each individual species over ten years and the results were used to estimate richness, diversity, and evenness for each herbicide use scenario. The repeated use of glyphosate alone had a minimal effect on richness, but it caused a strong reduction in weed diversity and evenness. Programs with more mechanisms of action and the use of both preemergence and postemergence herbicides were slightly more likely to suffer the loss of weed species than programs with single or just a few herbicides. Conversely, the former had a higher probability of maintaining weed diversity and evenness than the latter. According to simulations, losses in weed community diversity are reversible, especially when highly competitive species were eradicated allowing other species with lower lambda to increase their populations. However, the eradication of species with low reproductive rates reduced diversity and evenness. The effects of herbicide programs on the weed community lasted for several years even after those programs were modified indicating that seed banks play a major buffering role in the rate of change of weed community composition. Thus, frequent changes in management interrupting the repeated use of specific weed control programs, even under high herbicide intensity use (i.e., number of applications and mechanisms of action), can help maintain weed diversity in agroecosystems.}, journal={EUROPEAN JOURNAL OF AGRONOMY}, author={Oreja, Fernando H. and Inman, Matthew D. and Jordan, David L. and Bardhan, Deepayan and Leon, Ramon G.}, year={2022}, month={Aug} }
 @article{oreja_inman_jordan_leon_2021, title={Population growth rates of weed species in response to herbicide programme intensity and their impact on weed community}, volume={9}, ISSN={["1365-3180"]}, url={https://doi.org/10.1111/wre.12509}, DOI={10.1111/wre.12509}, abstractNote={Abstract The adoption of dicamba‐tolerant crops has reduced the challenge of controlling glyphosate‐resistant Amaranthus palmeri in these crops. However, introducing herbicide programmes with new mechanisms of action and different intensities can favour major shifts in weed communities. This can affect not only the functionality of the agroecosystem, but also resource availability to the most problematic species. The objectives of this work were to evaluate how herbicide programme structure and intensity affect (a) weed diversity, (b) population growth rate (λ) of weed species and (c) weed community structure based on λ dynamics in a dicamba‐tolerant cotton monoculture. To achieve these objectives, a cotton field experiment was established to compare four herbicide programmes from 2011 to 2018. The herbicide programmes differed in the first 4 years (i.e. glyphosate every year, alternating glyphosate and glyphosate plus dicamba every other year, glyphosate plus dicamba every year, and residual herbicide and glyphosate plus dicamba every year). During the last 4 years, all programmes received glyphosate plus dicamba. The weed seedbank was evaluated every spring and λ calculated. Environmental variation from year to year was more important in determining weed richness than herbicide programmes, which exhibited similar richness across all treatments during the eight years of the study. Regardless of herbicide programme, most species maintained λ between zero and one. Only a few species were the exception with λ values above one, such as A . palmeri , Mollugo verticillata and Eleusine indica . Although glyphosate plus dicamba reduced λ for several species, this herbicide mix was less effective in reducing λ for other weeds compared with glyphosate alone, suggesting a potential antagonism that could change weed community composition. The limited changes in λ for most species suggest the capacity of weeds to adjust reproduction and survival to overcome changes in mortality rates caused by increases in herbicide use intensity.}, journal={WEED RESEARCH}, publisher={Wiley}, author={Oreja, Fernando H. and Inman, Matthew D. and Jordan, David L. and Leon, Ramon G.}, year={2021}, month={Sep} }