Scholarly Works, School of Plant and Environmental Sciences

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Subsidy-stress responses of ecosystem functions along experimental freshwater salinity gradients
DeVilbiss, Stephen E.; Badgley, Brian D.; Hotchkiss, Erin R.; Steele, Meredith K. (Springer, 2024-05-01)
Human activity is increasing salt concentrations in freshwaters worldwide, but effects of freshwater salinity gradients on biogeochemical cycling are less understood than in saline, brackish, or marine environments. Using controlled microcosm experiments, we characterized (1) short-term (one to five days) biogeochemical responses and (2) water column metabolism along a freshwater salinity gradient of multiple salt types. After one day, microcosms were oxic (4.48-7.40 mg O2 L-1) but became hypoxic (1.20-3.31 mg L-1) by day five. After one day in oxic conditions, microbial respiration in magnesium-, sodium-, and sea salt-based salinity treatments showed a subsidy-stress response, with respiration increasing by over 100% as salinity increased from 30 to 350-800 mu S cm-1. Conversely, respiration consistently increased along a calcium-based salinity gradient, peaking at 1500 mu S cm-1. By day five, an inverse subsidy-stress response was observed with elevated respiration at upper or lower ends of the gradient except for the magnesium treatment, which had the lowest respiration at the highest salinity. Calcium- and magnesium-based salinity treatments also caused considerable changes in phosphorus concentrations and C:P and N:P. In a separate experiment, microbial respiration and water column primary production also displayed subsidy-stress responses, but imbalances in effect sizes caused consistently declining net community production with increasing salinity. Collectively, our results establish that short-term exposure to different salt ion concentrations can enhance freshwater biogeochemical cycling at relatively low concentrations and alter resource stoichiometry. Furthermore, the nature of effects of freshwater salinization may also change with oxygen availability.
Using hyperspectral signatures for predicting foliar nitrogen and calcium content of tissue cultured little-leaf mockorange (Philadelphus microphyllus A. Gray) shoots
Khajehyar, Razieh; Vahidi, Milad; Tripepi, Robert (Springer, 2024-06-01)
Determining foliar mineral status of tissue cultured shoots can be costly and time consuming, yet hyperspectral signatures might be useful for determining mineral contents of these shoots. In this study, hyperspectral signatures were acquired from tissue cultured little-leaf mockorange (Philadelphus microphillus) shoots to determine the feasibility of using this technology to predict foliar nitrogen and calcium contents. After using a spectroradiometer to take hyperspectral images for determining foliar N and Ca contents, the correlation between the hyperspectral bands, vegetation indices, and hyperspectral features were calculated from the spectra. Features with high correlations were selected to develop the models via different regression methods including linear, random forest (RF), and support vector machines. The results showed that non-linear regression models developed through machine learning techniques, including RF methods and support vector machines provided satisfactory prediction models with high R-2 values (%N by RF with R-2 = 0.72, and %Ca by RF with R-2 = 0.99), that can estimate nitrogen and calcium content of little-leaf mockorange shoots grown in vitro. Overall, the RF regression method provided the most accurate and satisfactory models for both foliar N and Ca estimation of little-leaf mockorange shoots grown in tissue culture.
PFAS fate using lysimeters during degraded soil reclamation using biosolids
Peter, Lynda; Modiri-Gharehveran, Mahsa; Alvarez-Campos, Odiney; Evanylo, Gregory K.; Lee, Linda S. (Wiley, 2025-01-01)
Carbon- and nutrient-rich biosolids are used in agriculture and land reclamation. However, per- and polyfluoroalkyl substances (PFAS) typically present in biosolids raise concerns of PFAS leaching to groundwater and plant uptake. Here, we investigated PFAS persistence and leaching from biosolids applied to a site constructed artificially to mimic degraded soils. Treatments included biosolids and biosolids blended with mulch applied at different rates to attain either one and five times the agronomic N rate for vegetable crops and a control treatment with synthetic urea and triple superphosphate fertilizer. Leachates were collected for a 2-year period from 15-cm depth zero-tension drainage lysimeters. Soils were analyzed post biosolids application. PFAS were quantified using isotope-dilution, solid-phase extraction and liquid chromatography tandem mass spectrometry. Leachate profiles exemplified an initial high total PFAS concentration, followed by a sharp decline and subsequent small fluctuations attributed to pre-existing soil conditions and rainfall patterns. Quantifiable PFAS in leachate were proportional to biosolids application rates. Short-chain perfluoroalkyl acids (CF2 < 6) were dominant in leachate, while the percentage of longer chains homologues was higher in soils. A 43% biosolids blend with mulch resulted in 21% lower PFAS leachate concentrations even with the blend application rate being 1.5 times higher than biosolids due to the blend's lower N-content. The blending effect was more pronounced for long-chain perfluoroalkyl sulfonic acids that have a greater retention by soils and the air-water interface. Biosolids blending as a pragmatic strategy for reducing PFAS leachate concentrations may aid in the sustainable beneficial reuse of biosolids.
On-farm large plot comparison of Bt and non-Bt corn hybrids for Helicoverpa zea (Lepidoptera: Noctuidae) feeding, yield, and economic return
Alsdorf, Alexis; Reisig, Dominic; Ferraro, Gregory; Malone, Sean; Mott, Joshua; Schardong, Igor; Taylor, Sally; Rejesus, Roderick (Oxford University Press, 2025-11-16)
Helicoverpa zea (Bodie) is a widespread damaging pest in the US that has evolved varying levels of resistance to Cry toxins in corn and cotton. To delay resistance evolution to this pest and others targeted by Bt corn, growers in the southern United States are required to plant at least 20% of their corn area with non-Bt corn. However, growers are reluctant to do this. Multiple small-plot research studies show timely planted non-Bt and Bt corn hybrids yield equally; however, growers often think non-Bt hybrids yield less than Bt hybrids. In response, we compared non-Bt and Bt hybrids using grower-owned planting and harvesting equipment. Growers planted 5 corn hybrids as strip plots (Bt-P1197YHR, DKC65-99, non-Bt-P1197LR, DKC67-70, and DKC65-93) in 2022 at 27 locations and 4 hybrids (excluding DKC65-93) in 2023 at 28 locations throughout North Carolina. When corn reached dent (R5), we measured the area of H. zea injury from each hybrid at each location. We calculated yield and economic net returns at harvest. We separated analyses for Bt trait pyramid and hybrid for both feeding and yield. H. zea feeding was at moderate levels, following predictable patterns. There were no significant differences between Bt and non-Bt hybrids within the 2 companies we compared (Pioneer [P] and Bayer [DKC]) across both years. In general, farm profitability is not statistically different when planting a 20% non-Bt refuge compared to planting 100% Bt corn. Factors other than typical H. zea feeding are more impactful on yield in North Carolina.
Soil health indicators for predicting corn nitrogen requirement in long-term cover cropping
Pokhrel, Sapana; Maguire, Rory O.; Thomason, Wade E.; Stewart, Ryan D.; Flessner, Michael L.; Reiter, Mark S. (Wiley, 2024-09-01)
Efforts to address economic and environmental concerns surrounding nitrogen (N) have motivated attempts to improve estimates of plant-available N in soil. Several soil health indicators, including CO2 burst, permanganate oxidizable carbon (C) (POXC), and autoclaved-citrate extractable (ACE) soil protein, assess labile C and N, and therefore may help to estimate soil N mineralization in long-term cover cropping systems (>3 years). This study evaluated the relationship of CO2 burst, POXC, ACE-soil protein, and pre-sidedress nitrate test (PSNT) with agronomic optimum N rate (AONR) in corn (Zea mays L.). The study also looked at relationship between other soil test and corn yield parameters, relative yield (RY) and yield without N sidedress at 25 long-term cover crop sites across Virginia. Results showed relatively weak correlations between AONR and CO2 burst, POXC, ACE-soil protein, and NO3-N (r = 0.00 to -0.48), which indicates that these soil health tests may not reliably predict soil N availability and corn yield. Corn yield with zero-sidedress N rate had a negative relationship with cover crop C:N ratio (r = -0.66) and a positive relationship with cover crop N content (r = 0.59), and NO3-N at pre-planting (r = 0.54) and sidedress (PSNT) (r = 0.63). The PSNT showed a better relationship (r = 0.65) compared to 72-h CO2 burst (r = 0.48) with RY. Soil health indicators (CO2 burst, POXC and ACE-soil protein) resulted in a poor or no relationship with AONR. Our results indicate that the PSNT was a more reliable indicator of the sidedress N rate in corn.
Transgenerational phenotypic responses to herbicide stress are more rapid than to shade and simulated herbivory in Arabidopsis
Sharma, Gourav; Haak, David; Westwood, James H.; Askew, Shawn; Barney, Jacob N. (Wiley, 2024-09-01)
Weeds in agricultural settings continually adapt to stresses from ecological and anthropogenic sources, in some cases leading to resistant populations. However, consequences of repeated sub-lethal exposure of these stressors on fitness and stress "memory" over generations remain poorly understood. We measured plant performance over a transgenerational experiment with Arabidopsis thaliana where plants were exposed to sub-lethal stress induced by the herbicides glyphosate or trifloxysulfuron, stresses from clipping or shading in either one (G1) or four successive generations (G1-G4), and control plants that never received stress. We found that fourth-generation (G4) plants that had been subjected to three generations of glyphosate or trifloxysulfuron stress produced higher post-stress biomass, seed weight, and rosette area as compared to that produced by plants that experienced stress only in the first generation (G1). By the same measure, clipping and shade were more influential on floral development time (shade) and seed weight (clipping) but did not show responsive phenotypes for vegetative metrics after multiple generations. Overall, we found that plants exhibited more rapid transgenerational vegetative "stress memory" to herbicides while reproductive plasticity was stressor dependent and similar between clipping/shade and anthropogenic stressors. Our study suggests that maternal plant stress memory aids next-generation plants to respond and survive better under the same stressors. We show differential transgenerational phenotypes to different stressors over four generations in Arabidopsis.
Estimates of soil taxonomic change due to near-surface permafrost loss in Alaska
Jelinski, N. A.; Pastick, N. J.; Kholodov, A. L.; Sousa, M. J.; Galbraith, John M. (Wiley, 2024-09-01)
Gelisols (permafrost-affected soils in US Soil Taxonomy) are extensive in Alaska, currently occurring on similar to 45% of the land area of the state. Gelisol taxonomic criteria rely on the presence of near-surface (less than 2 m deep) permafrost, but ongoing climatic and environmental change has the potential to affect the presence of near-surface permafrost across much of Alaska throughout the 21st century. In this study, we utilized scenarios of near-surface permafrost loss and active layer deepening through the 21st century under low (SRES B1, RCP 4.5), mid- (SRES A1B), and high (SRES A2, RCP 8.5) emissions scenarios, in conjunction with the statewide STATSGO soil map, to generate spatially explicit predictions of the susceptibility of Gelisols and Gelisol suborders to taxonomic change in Alaska. We find that 15%-53% of Alaskan Gelisols are susceptible to taxonomic change by mid-century and that 41%-69% of Alaskan Gelisols are susceptible to taxonomic change by the end of the century. The extent of potential change varies between suborders and geographic regions, with Gelisols in Northern Alaska being the most resilient to taxonomic change and Western and Interior Alaskan Gelisols most susceptible to taxonomic change. The Orthel suborder is likely to be highly restricted by the late 21st century, while Histels and Tubels are more likely to be of greater extent. These results should be taken into consideration when designing initial survey and re-mapping efforts in Alaska and suggest that Alaskan Gelisol taxa should be considered threatened soil taxa due to the proportional extent of likely loss. Fifteen to fifty-three percent of Alaskan Gelisols are susceptible to taxonomic change by 2050-2059. forty-one to sixty-nine percent of Alaskan Gelisols are susceptible to taxonomic change by 2090-2099. Extent of taxonomic change is the highest in the Interior and lowest in Northern Alaska. Susceptibility to change differs by land resource region and Gelisol suborder.
Leveraging deep learning for dollar spot detection and quantification in turfgrass
Kitchin, Elisabeth C. A.; Sneed, Henry J.; McCall, David S. (Wiley, 2025-01-01)
This study evaluates the effectiveness of fine-tuning a semantic segmentation model to identify and quantify dollar spot in turfgrasses, the most extensively managed and researched disease of turfgrasses worldwide. Using the DeepLabV3+ model, recognized for its capability to segment complex shapes and integrate multi-scale contextual information, the research leveraged a diverse dataset comprising various turfgrass species, disease stages, and lighting conditions to ensure robust model training. The trained model is able to identify and segment disease instances accurately and precisely, and the results indicate the potential for model-based assessment to outperform traditional visual assessment methods in speed, accuracy, and consistency. The development of deep learning models on extensive datasets like ImageNet requires significant computational resources. However, by fine-tuning a pretrained semantic segmentation model, we adapted it for disease segmentation using only a standard personal computer's graphics processing unit. This approach not only conserves resources but also highlights the practicality of deploying advanced deep learning applications in turfgrass pathology with limited computational capacity. The proposed model provides a new tool for turfgrass researchers and professionals to rapidly and accurately quantify this important disease under real-world growing conditions. Additionally, the findings suggest the potential to apply deep learning algorithms to other turfgrass diseases to support data-driven decisions. This could enhance disease management practices and improve decision-making processes for fungicidal treatments, thereby improving the economic and environmental sustainability of turfgrass management. Dollar spot is one of the most commonly studied turfgrass diseases, with researchers manually counting infection centers for quantification. A deep learning model was used to detect and quantify dollar spot from field research images. The dollar spot detection model accurately estimated dollar spot with limited false positives or false negatives. Described methods provide a tool for turfgrass scientists and professionals to rapidly quantify dollar spot from field images.
The impact of imidacloprid on the subterranean survivorship of Laricobius (Coleoptera: Derodontidae), a biological control agent of Adelges tsugae (Hemiptera: Adelgidae)
Hillen, Ashleigh P.; Foley, Jeremiah R.; Gross, Aaron D.; Mayfield III, Albert E.; Williams, Jacob; Xia, Kang; Salom, Scott M. (Wiley, 2025-05-01)
The invasive hemlock woolly adelgid (HWA), Adelges tsugae (Annand) (Hemiptera: Adelgidae), has spread throughout most of the range of eastern hemlock, Tsuga canandensis (L.), and the entire range of Carolina hemlock, Tsuga caroliniana (Engelman), in the United States. Integrated pest management (IPM) of HWA combines chemical applications with the release of biological control agents on untreated trees within the same stand. Laricobius spp., Rosenhauer (Coleoptera: Derodontidae), have been used as biological control agents of HWA since 2003 and have subterranean and arboreal life phases that are synchronous with HWA's lifecycle. When utilizing IPM tactics, there is potential for Laricobius spp. to settle below an insecticide-treated tree for its subterranean phase. Field investigations assessed the impact of historical (five years post treatment in 2017) and recent imidacloprid soil treatments (via soil injection, soil drench, and tablet in November 2020) on the subterranean survivorship of Laricobius spp. by quantifying concentrations of imidacloprid and its metabolites to determine its potential impact on percent adult emergence from the soil. We observed a significant treatment effect on mean soil concentration among application methods at the recent treatment site, but not the historical treatment site. Additionally, at the more recently treated site, significantly lower mean percent emergence was observed from soil drench and tablet imidacloprid applications after one year (2021), but by the following year (2022), that effect was no longer present. This study supports recent recommendations to delay releases of Laricobius spp. for one-year post-treatment with imidacloprid. Furthermore, these data suggest when applying imidacloprid to a stand established with Laricobius spp., soil injection techniques pose the least risk to their subterranean survivorship.
Spatial–Temporal Patterns of Methane Emissions from Livestock in Xinjiang During 2000–2020
Xu, Qixiao; Li, Yumeng; You, Yongfa; Zhang, Lei; Zhang, Haoyu; Zhang, Zeyu; Yao, Yuanzhi; Huang, Ye (MDPI, 2025-10-11)
Livestock represent a significant source of methane (CH₄) emissions, particularly in pastoral regions. However, in Xinjiang—a pivotal pastoral region of China—the spatiotemporal patterns of livestock CH₄ emissions remain poorly characterized, constraining regional mitigation actions. Here, a detailed CH₄ emissions inventory for livestock in Xinjiang spanning the period 2000–2020 is compiled. Eight livestock categories were covered, gridded livestock maps were developed, and the dynamic emission factors were built by using the IPCC 2019 Tier 2 approaches. Results indicate that the CH₄ emissions increased from ~0.7 Tg in 2000 to ~0.9 Tg in 2020, a 28.5% increase over the past twenty years. Beef cattle contributed the most to the emission increase (59.6% of total increase), followed by dairy cattle (35.7%), sheep (13.9%), and pigs (4.3%). High-emission hotspots were consistently located in the Ili River Valley, Bortala, and the northwestern margins of the Tarim Basin. Temporal trend analysis revealed increasing emission intensities in these regions, reflecting the influence of policy shifts, rangeland dynamics, and evolving livestock production systems. The high-resolution map of CH₄ emissions from livestock and their temporal trends provides key insights into CH₄ mitigation, with enteric fermentation showing greater potential for emission reduction. This study offers the first long-term, high-resolution CH₄ emission inventory for Xinjiang, providing essential spatial insights to inform targeted mitigation strategies and enhance sustainable livestock management in arid and semi-arid ecosystems.
Impact of species selection on plant community, sod tensile strength, and translocation rooting of a pollinator-garden sod
Askew, Whitnee B.; Godara, Navdeep; Brewer, John R.; Goncalves, Clebson G.; Goatley, Michael; Askew, Shawn D. (Wiley, 2024-11-01)
Interest in pollinator gardens is increasing to address pollinator decline. The establishment of perennial native plants often takes a few years and establishment projects are often lost to competition from unwanted weedy vegetation. Mature sod of pollinator-serving, native plants that is free of weeds would be highly desirable to conventional turfgrass sod consumers, thus offering a new revenue stream for traditional sod producers. The objective of this study is to evaluate the influence of four foundational species treatments on 3-year floral biodiversity of pollinator-serving plants, sod tensile strength, and transplant rooting strength. Results suggest that polycultures of pollinator-serving forbs can produce a marketable sod with sufficient tensile strength for lifting and translocating and sufficient ability to establish once relocated. Sod tensile strength, however, is insufficient for lifting when the plant community is not grown over plastic or does not contain a high-shoot density or rhizomatous foundation species such as hard fescue (Festuca longifolia Thuill.) or common yarrow (Achillea millefolium L.). Unfortunately, adding hard fescue or common yarrow markedly reduces the Shannon diversity index and species richness. The force needed to lift transplanted sod after 3 months was 5553 to 6969 N m-2 regardless of foundation species treatment and was numerically higher than the force reported by previous researchers to lift sod of various turfgrass species. Collectively, the data suggest that the best balance between preserving floral biodiversity and maximizing sod handling integrity would be approached by establishing pollinator-serving forbs alone or with a blend of native grasses over plastic. Mature, weed-free sod of native pollinator-serving plants offers a potential new revenue source for sod producers. Polycultures of pollinator-serving forbs yielded marketable sod with good tensile strength and transplant success. Optimal floral diversity and sod handling is achieved by planting forbs alone or with native grasses over plastic.
Blend ratios and mixtures of brown patch susceptible and resistant tall fescue cultivars
Powlen, Jada S.; McCall, David S.; Hensler, Kevin L.; Kerns, James P.; Fidanza, Michael A.; Bigelow, Cale A. (Wiley, 2024-11-01)
Brown patch (Rhizoctonia spp.) is a major disease of turf-type tall fescue (TF) [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]. Many cool-season turfgrass lawns consist of species mixtures or cultivar blends, but the exact proportion of resistant cultivars in blends and mixtures to effectively reduce disease has not been well documented. A field study was conducted in West Lafayette, IN, and Blacksburg, VA, during 2022 and 2023 to determine the brown patch severity of various blend ratios (0%, 25%, 50%, 75%, and 100% by weight) using a brown patch susceptible and resistant TF cultivar. Additionally, mixtures (90% and 10% by weight, respectively) of TF and Kentucky bluegrass (Poa pratensis L.) with a susceptible and resistant TF cultivar were evaluated. Seasonal appearance/turf quality and brown patch severity were visually determined, and area under the disease progress curve (AUDPC) was calculated. Turf quality and brown patch severity were similar at both locations. Additionally, blends and mixtures containing >= 75% of the resistant cultivar maintained higher average visual quality across both locations compared to the susceptible cultivar alone. Between the two mixtures, the inclusion of a resistant TF cultivar maintained higher canopy density and increased the proportion of TF at both locations. Blends and mixtures containing >= 75% of a resistant cultivar reduced brown patch AUDPC by 71% and 83% in 2022 and 2023, respectively, when compared to the 100% susceptible cultivar. This field study reinforces the importance of selecting resistant TF cultivars to reduce seasonal brown patch symptoms in cool-season turfgrass lawns. Increasing the proportion of a resistant tall fescue cultivar in a blend significantly reduced brown patch severity. Turfgrass quality increased as the proportion of a resistant tall fescue cultivar increased in a blend. A brown patch-resistant cultivar in tall fescue: Kentucky bluegrass mix increased density and fescue composition. The proportion of Kentucky bluegrass significantly increased over time in tall fescue: Kentucky bluegrass mixtures.
A method to spatially assess multipass spray deposition patterns via UV fluorescence and weed population shifts
Koo, Daewon; Godara, Navdeep; Cubas, Juan R. Romero; Askew, Shawn D. (Wiley, 2025-01-01)
Spray deposition patterns from agricultural sprayers are traditionally sampled discretely along a field transect accounting for 0.5% or less of the treated area. Such methods may not fully capture the dimensional variability inherent in large-scale, multiple-pass spray applications, especially evident from an agricultural spray drone (ASD). This study investigated the utilization of UV-fluorescent dye and nighttime aerial imaging techniques to assess large-scale, multipass spray deposition patterns. Accuracy of digital hue from UV-fluorescent photography to predict deposition of proxy dye was confirmed via fluorometry assessed intensity levels of extracted UV-fluorescent dye from 384 Petri dishes placed prior to treatment. Results showed that ASD applications, regardless of nozzle type, exhibited greater spatial variability within the target area compared to ride-on sprayer applications, primarily due to overapplication. Additionally, the ASD generated spray drift to adjacent nontarget areas that was at least three times more than that of ride-on and spray-gun sprayers. Multipass deposition was further assessed via in situ smooth crabgrass infestation following treatment with quinclorac or topramezone by multipass ASD or hand-held, four-nozzle spray boom. Weed infestation annotated from overlaid grids with 9.3-dm2 ground resolution inconsistently detected spatial heterogeneity between transects assessed along the center and edge of each sprayer pass. The ASD controlled smooth crabgrass 11% more than the hand-held sprayer, albeit with an 18% increase in spray drift to nontarget areas, similar to the UV-fluorescence study. Digitally assessed average hue of fluorescence photography appears to be a viable method to assess multidimensional and continuous spatial relationships of spray deposition. Traditional spray deposition assessments lack spatial dimensionality. Nighttime UV-fluorescence photography of proxy dye accurately assesses spray deposition patterns. Spatial heterogeneity and drift increase with agricultural spray drones compared to ride-on sprayers. Weed infestation annotated via grid-overlaid aerial images resolves drift more than spatial heterogeneity. Despite erratic deposition, spray drones conserve or enhance weed control compared to a handheld boom sprayer. Spraying herbicides evenly is crucial for effective weed control. While the use of agricultural spray drones is increasing, there is limited understanding of their spray uniformity and drift potential. Inconsistent spray patterns can lead to overapplication or under-application, reducing weed control efficacy, or causing unintended crop damage. This study examined how agricultural spray drones, ride-on sprayers, and handheld spray guns distribute herbicides, using UV-fluorescent dye and nighttime imagery or aerial photos to detect weed population shifts. Results showed that ride-on sprayers applied chemicals more evenly, while drones and spray guns had more overapplication, especially with drones spraying too much directly below. Drones also caused more drift, but they achieved better weed control potentially due to fine spray particles covering more weeds. Although drones are less uniform, they can be effective for weed control but pose a higher risk of environmental impact through drift.
The bioherbicide Verticillium nonalfalfae effectively removes tree-of-heaven (Ailanthus altissima) but leaves many other non-native plants
Shively, Timothy J.; Barney, Jacob N.; Reid, J. Leighton; Salom, Scott M. (Cambridge University Press, 2024-12-01)
Tree-of-heaven [Ailanthus altissima (Mill.) Swingle] readily exploits disturbances, grows quickly into dense monocultures, and suppresses native plant species. The vascular wilt pathogen, Verticillium nonalfalfae, native to the eastern United States, has been proposed as a biocontrol agent for the invasive A. altissima. Studies consistently demonstrate the safety and efficacy of the bioherbicide, but they also note that the selective nature of the fungus does not preclude other invasive plants that commonly co-occur with A. altissima from occupying the site. We quantified the standing plant community and seedbank at several sites across Virginia 5 yr after inoculation with V. nonalfalfae to understand which species are present or being naturally recruited. Ailanthus altissima remained dominant in untreated areas but was nearly eradicated from the treatment plots. Other non-native species made up a large portion of the plant community and seedbank across all study areas, with no differences in their respective cover and count between treatments. While variability in plant community composition is high and site-specific context is important for establishing effective management strategies, planting native species and mitigating other invasives will be crucial to ensuring native species successfully establish in bioherbicide-treated areas.
Agricultural spray drone deposition, Part 2: operational height and nozzle influence pattern uniformity, drift, and weed control
Koo, Daewon; Goncalves, Clebson G.; Askew, Shawn D. (Cambridge University Press, 2024-11-01)
Agricultural spray drone (ASD) use in managed turfgrass has been given limited attention in the scientific literature. Further, deposition patterns of ASD spray have been obscured in previous research by ambient wind, crop canopy interference, and limited sampling resolution. Using a continuous sampling method involving blue colorant and water sprayed over white Kraft paper that was assessed via digital image analysis of stain objects and referenced spectrophotometric analysis of extractant, deposition metrics were estimated across a 29.3-m transect perpendicular to an ASD or ground-sprayer spray swath. The ASD applies very fine droplets that are highly concentrated with herbicide, similar to ultra-low volume treatments, that improved smooth crabgrass [ Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] control compared with a ground sprayer when the ASD was operated 2 m above the turf. Unfortunately, these very fine droplets also drift, leading to four times greater droplet density at distance of almost 12 m away from the targeted spray swath following an operational height of 10 m compared with 2 m. As ASD operational height increases, drift and effective swath width at 30% coefficient of variation uniformity increases, while effective application rate, total deposition, and D. ischaemum control by quinclorac herbicide decreased. Total deposition decreased 6% for each meter increase in ASD operational height, likely due to evaporation. The potential losses due to evaporation are a serious consideration for ASD use that has received little attention in the scientific literature. Our data suggest that ASD operational height should be as low as possible, but modification of spray systems may be needed to improve homogeneity of spray pattern.
Agricultural spray drone deposition, Part 1: methods for high-throughput spray pattern analysis
Koo, Daewon; Henderson, Caleb A.; Askew, Shawn D. (Cambridge University Press, 2024-11-01)
Effective pesticide application is dependent on precise and sufficient delivery of active ingredients to targeted pests. Water-sensitive papers (WSPs) have been used to estimate the stain coverage, droplet density, droplet size, total spray volume, and other spray-quality metrics by analyzing deposit stains using image analysis software. However, because WSPs are expensive, they are typically distributed along unidimensional transects at intervals of 0.5 m or more, which comprises 0.5% or less of the total treated area. This might limit the ability to accurately represent the deposition of agricultural sprayers with irregular patterns, such as agricultural drone sprayers in the early developmental stage. This study introduces a novel approach utilizing white Kraft paper and a blue colorant proxy for assessing spray deposition. A custom Python-based image analysis tool, SprayDAT (Spray Droplet Analysis Tool), was developed and compared with traditional image analysis software, DepositScan. Both models showed increased accuracy in detecting larger objects, with SprayDAT generally performing better for smaller droplets. DepositScan underestimated the total deposited spray volume by up to 2.7 times less compared with the colorant extraction assessed via spectrophotometry and the predicted output based on flow rate, coverage, and speed. Accuracy of software-estimated spray volume declined with increasing total stain coverage, likely due to overlapping stain objects. Droplet density exhibited a Gaussian trend, with peak density at approximately 22% stain cover, offering evidence for overlapped stains for both DepositScan and SprayDAT as stain cover increased. Both models showed exponential growth in volumetric median diameter (VMD) with increasing stain cover. SprayDAT is freely accessible through an online repository. It features a user-friendly interface for batch processing large sets of scanned images and offers versatility for customization to meet individual needs, such as adjusting spread factor, updating the standard curve for spray volume estimation, or modifying the stain detection threshold.
Cereal rye cover crop termination management for Palmer amaranth (Amaranthus palmeri) suppression in soybean
Sias, Cynthia; Bamber, Kevin W.; Flessner, Michael L. (Cambridge University Press, 2024-10-30)
Palmer amaranth is a troublesome weed species displaying the ability to adapt and evolve resistance to multiple herbicide modes of action, and additional weed suppression tactics are needed. Growing interest in the use of cover crops (CCs) has led to questions regarding the most appropriate forms of CC management prior to cash crop planting in order to maximize weed suppression benefits. Experiments were conducted between 2021 to 2023 to test 1) cover crop termination timing (i.e., green or brown); 2) CC biomass amount; and 3) CC termination method (i.e., rolled or left standing) on Palmer amaranth suppression. Treatments included "planting brown" (cereal rye terminated 2 wk before soybean planting), "planting green" (cereal rye terminated at soybean planting), and a no-CC (winter fallow) check. Palmer amaranth emergence was evaluated at 4 and 6 wk after soybean planting, and yield was calculated at harvest. Palmer amaranth emergence was reduced when a CC was planted compared with the no-CC check, and more suppression was observed as CC biomass increased. This decrease in emergence is potentially due to a decrease in light reaching the soil surface and physical suppression as CC biomass increased. Yield, however, was unaffected by any CC management practice, indicating that growers can tailor CC termination practices for weed suppression. This information will provide better recommendations for farmers interested in using CCs for weed suppression. Overall, the importance of CC biomass accumulation to achieve weed suppression is highlighted in our findings. Additionally, we add to the growing body of documentation that soybean yield may be variable from year to year as a result of CC presence.
Auxin herbicides, halosulfuron, sulfentrazone, and topramezone disparately affect morphology and ultraviolet features of weedy flowers and associated pollinator foraging
Godara, Navdeep; Askew, Shawn D. (Cambridge University Press, 2024-11-01)
Pollinators risk exposure to insecticide residue when visiting weedy flowers in urban landscapes. Previous research shows that pollinators are routinely exposed to a variety of pesticides, but herbicides have exhibited minimal toxicity and did not contribute to the modeled risk quotients. Herbicides from different modes of action may deter pollinators from visiting turfgrass weeds, but their temporal influence on floral quality and pollinator foraging is unaddressed. Research experiments were conducted at Blacksburg, VA, in 2023 to assess the effect of four herbicides on floral morphology and ultraviolet (UV) reflectance of three different UV floral classes of weeds and associated pollinator foraging visits. Among 1,080 assessments per weed species, honeybees ( Apis mellifera), bumble bees ( Bombus spp.), solitary bees ( Chelostoma florisomne), and flies ( Diptera spp.) accounted for 94%, 2%, 3%, and 1%, respectively, of the total pollinator visitations on white clover ( Trifolium repens L.) inflorescences; 71%, 2%, 0%, and 27%, respectively, on dandelion ( Taraxacum officinale F.H. Wigg.) flowers; and 0%, 0%, 78%, and 22%, respectively, on bulbous buttercup ( Ranunculus bulbosus L.) flowers. Pollinator visitation and floral quality were temporarily affected by herbicide application, with some herbicides eliminating food resources, while others transiently impacted floral quality and density. The combination of 2,4-D + dicamba + MCPP and topramezone eliminated pollinator foraging visits, but on differing temporal scales of 3 d for auxins and 14 d for topramezone. Halosulfuron and sulfentrazone transiently suppressed floral quality and density, with varying degrees of deterrence on pollinators depending on the weed species. All evaluated herbicides reduced radiometric UV reflectance of T. officinale petal apices, but only synthetic auxin and topramezone reduced digitally assessed floral UV- reflecting area. Petal UV reflectance appears to contribute but not solely influence pollinator foraging behavior. UV-absorbing and UV-reflecting flowers differed in UV-reflectance response to herbicides, but pollinators were similarly deterred. Results suggest that herbicides may offer a variety of management solutions to pollinator deterrence in areas slated for insecticide treatment, including long-term or transient deterrence with potential food-resource preservation.
Optimizing liquid-applied iron sulfate rate and application interval for dollar spot suppression on golf course fairways
Soldat, D. J.; Hockemeyer, K.; McCall, David S.; Straw, C. M.; Koch, P. L. (Wiley, 2025-01-01)
Iron sulfate applications reduce dollar spot severity on golf course turfgrass, but further optimizing the use of iron sulfate may increase efficacy and encourage more widespread adoption by golf course superintendents. Three iron sulfate rates (9, 18, 36 kg ha-1), two application intervals (7 and 14 days), three water volumes (306, 612, and 1223 L ha-1), and combinations with fertilizer and fungicide products were evaluated at field locations in Madison, WI, Bloomington, MN, and Blacksburg, VA, in 2018 and 2019. Iron sulfate rate decreased dollar spot at all locations in a dose-dependent manner, and 7-day applications were more efficacious than 14-day applications. Water volume had no impact on disease severity at any location and combining iron sulfate with fertilizer had minimal impact as well. These results demonstrate improved iron sulfate strategies for dollar spot management and can be implemented by golf course superintendents in areas where fungicide resistance and fungicide regulations limit the use of traditional fungicides.
Optimizing fungicide application timing for spring dead spot based on soil temperature and season
Hutchens, W. J.; Booth, J. C.; Goatley, J. Michael Jr.; Roberson, T. L.; McCall, David S. (Wiley, 2025-01-01)
Spring dead spot (SDS) (Ophiosphaerella spp.) is the most detrimental disease to warm-season turfgrasses in areas with cold-induced dormancy. Fungicide applications do not provide consistent SDS suppression. One reason for this inconsistency is the use of solely calendar-based fungicide applications instead of considering both calendar date and soil temperature. A field study was conducted at three separate hybrid bermudagrass (Cynodon dactylon (L.) Pers. x transvaalensis Burtt Davy) locations in Virginia to determine the optimal soil temperature and timing for SDS suppression with tebuconazole and isofetamid. Tebuconazole (1.5 kg a.i. ha-1) and isofetamid (4.1 kg a.i. ha-1) were applied at 11 different timings throughout the year based on soil temperatures at a 0- to 10-cm depth. Plots were assessed for SDS severity in the spring and early summer of 2021 and 2022. Two in vitro studies were also conducted with Ophiosphaerella herpotricha and Ophiosphaerella korrae isolates to (1) determine the optimal temperature for growth on potato dextrose agar (PDA) placed on a thermogradient table (13-33 degrees C) and (2) compare the daily growth rate of O. herpotricha and O. korrae isolates at 11, 19, and 27.5 degrees C on PDA. In the field study, isofetamid suppressed SDS more than tebuconazole. Fall applications when soil temperatures were 13 degrees C consistently provided the best SDS suppression. For the in vitro studies, both species grew optimally between 24 and 25 degrees C, yet O. korrae and O. herpotricha growth rates differed at 11 degrees C.

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