Evaluation of Plant Hormones and Other Seed Treatments to Reduce Injury Caused by Preemergent Herbicides on Direct-seeded Turnips and Collard Greens - Matthew Cutulle Flaming, Cultivation, and Handweeding Weed Control in Organic Carrot Production Systems with Different Fertilizer Types - Peter Dittmar Tolerance of Peppermint to Herbicides Applied Post-Harvest - Stephen Meyers Developing a Biobased, Compostable Mulch that Crops Grow Through - Samuel Wortman Evaluating Application Approaches for Enhancing the Weed Suppression Effectiveness and Crop-Safety of Preemergence Herbicides in Vegetable Plasticulture Production - Ramdas Kanissery
Poor competitive ability and limited herbicide options make weed management of Brassica crops difficult. Growers often adopt the use of transplants, which is less efficient in terms of time, material, and labor when compared with direct seeding, resulting in higher prices per unit. Seed treatment with protective compounds could decrease crop injury from preemergent (PRE) herbicides making it profitable to direct-seed Brassica plants for production. Research was conducted to evaluate the ability of three candidate safeners [24-epibrassinolide, melatonin, and ascorbic acid (AsA)] to reduce injury caused by four herbicides (S-metolachlor, pyroxasulfone, halosulfuron, and mesotrione) applied PRE on the collard green cultivar Top Bunch and turnip cultivar Purple Top White Globe. Two independent greenhouse trials were conducted at the Clemson University Coastal Research and Education Center in Charleston, SC. Visual injury of the treated plants was evaluated weekly and dry mass was collected 21 days after treatment. Seed treatment did not reduce injury efficiently caused by pyroxasulfone, halosulfuron, and mesotrione; all doses were lethal for both crops. However, collard seeds treated using melatonin and AsA had 66% and 54% less injury caused by S-metolachlor at 514 g⋅ha–1 a.i., respectively. On turnips, melatonin was the only treatment that reduced the S-metolachlor damage on seedlings, with 43% less injury than untreated seedlings. Plant injury and plant weight correlated significantly for both Brassica crops. The reduction in injury caused by S-metolachlor when seeds were treated with melatonin and AsA validated those compounds’ protective ability. Seed treatment with melatonin could be combined with PRE applications of S-metolachlor to overcome the low weed competitive ability of these species early in the season.
Weed management is a common weed management practice in organic weed control, however, this practice is expensive. Other integrated weed management practice could include flaming and cultivation. The study objective is to investigate flaming, cultivation, and hand weeding to develop an integrated weed control program in organic carrot. The study was conducted in an organic certified field at the North Florida Research and Education Center Suwanee County, Live Oak, FL. Treatments were a factorial design with 5 weed management programs and 2 fertilizer types. Weed management treatments were (1) flaming preseeding weekly cultivation, (2) flaming preseeding weekly cultivation 1 handweeding event, (3) flaming preseeding flaming preemergence weekly cultivation (4) flaming preseeding flaming preemergence weekly cultivation 1 handweeding event, (5) flaming preseeding flaming preemergence weekly cultivation 2 handweeding events. Fertilizer treatments were pelleted poultry litter and 50% feather meal 50% poultry litter. Carrot ‘Uppercut’ were seeded on December 3, 2020 and were harvested on May 3, 2021. Eight rows of carrot were planted on a 0.9 m bed top. Fertilizer was applied immediately after seeding. Weeds were counted by species in two 0.5 m2 quadrats prior to each basket weeder cultivation between the rows. Carrots were cultivated 6 times before the carrot were too large and would be injured. Fertilizer type were not different for weed counts at all dates. Cutleaf evening primrose (Oenothera laciniata) was the only weed species in the plots from the beginning of the trial through harvest. The inclusion of flaming preplant and preemergence delayed the emergence of cutleaf evening primrose, however at 6 weeks after planting all the treatments were similar. Mid-season weed species included henbit (Lamium amplexicaule) and common chickweed (Stellaria media), however, these weed species were not present late-season. Purple toadflax (Linaria purpurea) and old world diamond flower (Oldenlandia corymbosa) were the most common weed species late-season. Single handweeding had excellent control early-season, but two handweeding events controlled both the cool and warm season weeds. Early season weed control should include flaming. Between row weed management was best with cultivation. Handweeding is necessary for late season weed control when flaming and cultivation are not available.
After harvest, peppermint is vulnerable to weed interference due to the loss of crop canopy. However, few herbicides are registered for use during this critical time in the production cycle. In response to this, we conducted research trials in 2023 at two commercial peppermint production fields in Indiana (North Judson and Fair Oaks) to determine peppermint response to preemergence and postemergence herbicides. Preemergence herbicide treatments included Zidua (1.84 fl oz/a), Optogen (3 fl oz/a), Spartan (4 fl oz/a), Chateau EZ (4 fl oz/a), Dual Magnum (1 pt/a), Fierce EZ (10 fl oz/a), and Tenacity (3 fl oz/a). Postemergence herbicide treatments included Basagran (2 pt/a), Reviton (2 fl oz/a), Tough (24 fl oz/a), Sharpen (2 fl oz/a), Anthem Flex (4.5 fl oz/a), Aim (1 fl oz/a), and Tough (24 fl oz/a) plus either Optogen (1.5 fl oz/a), Tenacity (1.5 fl oz/a), or Basagran (2 pt/a). Visible crop injury on a scale of 0 (no injury) to 100% (crop death), as well as crop height, was recorded every other week after treatment. Eight weeks after treatment, the greatest injury was observed was from the Group 14 herbicides: Reviton (81-84%), Sharpen (81-88%), and Aim (33-54%). Injury from Group 27 herbicides, Optogen and Tenacity, was more severe at Fair Oaks (63% and 64%, respectively) than at North Judson (28% and 12%, respectively). However, combining a half rate of these herbicides with Tough greatly increased crop injury at both locations (>73%). Injury from Chateau EZ and Fierce EZ differed by location; injury was lower at North Judson (13% and 7%, respectively) than at Fair Oaks (42% and 55%, respectively). Crop injury from Zidua, Dual Magnum, Spartan, Basagran, and Tough plus Basagran were similar to, or less than, Tough applied alone (the registered grower standard). Peppermint height and end-of-season aboveground biomass followed similar trends.
Plastic mulch films and geotextile landscape fabrics are not compatible with specialty crops grown at high densities with narrow in-row spacing. As a result, many growers resort to hand weeding these specialty crops, including leafy greens, carrots, and matted-row strawberries. Our objective was to develop and test value-added weed barrier mulches designed specifically for these crops to grow on and root through. We have conducted 13 trials across 3 crops (lettuce, carrot, and strawberry) and 3 years to evaluate 9 different biobased, compostable weed barrier mulches (BCMs) that include polylactic acid (PLA) resin. The BCMs tested varied in weight basis and material composition including: 1) PLA-only (80, 120, and 180 g/m2), 2) PLA embedded organic fertilizers (soybean meal and composted turkey litter; 150 and 210 g/m2), and 3) PLA paper (105 and 210 g/m2). The BCMs are installed in the field like a typical mulch film roll but are then covered with a 1 to 2.5 cm layer of compost (or other weed-free media) and crop seeds. Data was collected to evaluate effects of BCMs on weed density, soil nitrogen availability, moisture, and temperature, microbial abundance, and crop establishment, yield, and quality. Across all crops and site-years, BCMs reduced weed emergence by 80% to 97% compared to bare soil, and weed suppression was best in PLA paper. The BCMs immobilized some available soil nitrogen and embedded fertilizers in the BCM did not affect this outcome. In carrot, BCMs increased mycorrhizal fungi abundance by up to 59% compared to bare soil. In strawberry, BCMs increased crop canopy area by up to 51%. Yields were usually not different between BCMs and bare soil because weeds were removed weekly after counting. However, poor seedling establishment on BCMs due to heavy rainfall after planting in 2022 reduced carrot yield by 13% and lettuce yield by 20%. To address this issue, lettuce in 2023 was planted in two shallow seed furrows filled with compost on the BCM (instead of broadcast planting across the entire BCM bed top as in previous years). Lettuce establishment in the furrows was two times greater than in bare soil due to improved tilth and reduced erosion, and yield was not different from bare soil. Volumetric soil moisture in BCM compost seed furrows was 27.1% compared to 35.7% in bare soil, highlighting differences in texture and the importance of irrigation in the BCM system during establishment.
Preemergence herbicide application under plastic mulch is an effective strategy for managing weeds in vegetable plasticulture production. However, applying herbicides under plastic mulch in raised beds carries the inherent risk of crop phytotoxicity. This underscores the importance of exploring crop-safe methods for herbicide application in beds covered with plastic mulch. The study aimed to evaluate the efficacy of preemergence herbicide S-metolachlor alone or in combination with super absorbent polymer, soil binding agent, or compost in effectively controlling weeds in plastic mulched tomato beds without impacting the crops. During trials, I and II, preemergence S-metolachlor was applied either as blanket sprays or in combination with super absorbent polymer, soil binding agent, and compost on raised beds before installing plastic mulch. Results from trial II showed that S-metolachlor soil binding agent and S-metolachlor compost mix suppressed weed density by over 85% and 68%, respectively. Similarly, treatments including S-metolachlor alone, S-metolachlor super absorbent polymer, S-metolachlor soil binding agent, and S-metolachlor compost led to a reduction in weed biomass by over 50% compared to the non-treated control. Importantly, these treatments did not significantly impact tomato crop vigor and chlorophyll content during trials I and II, nor did they affect tomato crop biomass and yield. In conclusion, utilizing preemergence S-metolachlor along with different application approaches tested shows promise for controlling tough weeds such as nutsedge in tomato plasticulture beds.
Evaluating Efficacy of Organic Herbicides on Common Weed Species - Carly Strauser Evaluating Fall Cover Crops for Enhanced Soil Properties and No-Till Weed Suppression in Chickpea Production in Virginia - Zelalem Mersha Impact of Cover Crops and Herbicides on Early Season Weed Control and Sweetpotato Storage Root Yield. - Richard Noel Torres Effects of Row-middle Cover Crops on Strawberry Plasticulture Production - Jeanine Arana Palmer Amaranth and Waterhemp in the Pacific Northwest: Glyphosate Resistance Confirmation and Implications for Crop Production - Albert Adjesiwor Mesotrione and Simazine-Based Tank-Mixes for Late-Season Control of Doveweed in Bermudagrass Turf - Pawel Petelewicz Simulation-Based Nozzle Density Optimization for Maximized Efficacy of a Machine-Vision Weed Control System for Applications in Turfgrass Settings - Pawel Petelewicz Implementing Digital Multispectral 3D Scanning Technology for Rapid Assessment of Hemp (Cannabis sativa L.) Weed Competitive Traits - Tyler Campbell Farmer Experiences with Soil Tarping Across South Dakota - Hannah Voye
Soil tarping is a weed control method used by innovative farmers across the globe. Strategies used by farmers vary in terms of tarping material, time of application, length of time soil is covered, and the production goal. Solarization is a tarping technique that uses clear greenhouse plastic to harness light and energy from the sun to germinate weed seeds in the soil and exhaust the weed seed bank prior to a growing season. Occultation is another tarping technique that uses opaque tarps to warm the soil and stop light from germinating weed seeds or encouraging plant growth beneath the tarp. Researchers have taken an interest in exploring solarization and occultation impacts on weed suppression and soil health. During the 2023 and 2024 growing season, South Dakota State University soil tarping researchers collaborated with farmers across South Dakota to gain insight in farmer application of tarps. Farmer collaborators in South Dakota were each supplied with three tarp materials: black silage tarp, white silage tarp, and clear greenhouse plastic. Each farmer was told to use the tarp how they saw best fit for their operation. Farmers were given the opportunity to engage in field days and presentations to learn more about soil tarping. Each growing season, farmers worked with a team of researchers to collect data on soil temperature, moisture, and nitrogen. This data was collected through soil samples and HOBO moisture and temperature sensors that logged values hourly. Farmers also provided observations, photos, and dates for tarp removal and application along with comments on how well tarping fit into their system. While research studies can provide important details of tarping impacts on weed suppression and soil health, it is important to showcase the reality of how applicable this technique is for farmers in the real world.
A forum for discussion of potential collaborations with regards to plant growth and culture – i.e. propagation, root growth, water management, weed control, PGRs, plant nutrition, etc.
Cover crops offer multifaceted benefits including soil health improvement, nutrient management, erosion control, and suppression of pests, diseases and weeds. This study examined the impact of fall cover crop (FCC) for enhanced soil properties and suppression of weeds and diseases, top priorities for chickpea growers. FCC was comprised of winter rye alone (in 2021) or in combination with hairy-vetch (in 2022-2023). To assess soil property changes, 5 quadrants (50 cm x 50 cm) representing each dense (≥ 96%), poor (10-35%) and no-growth (0%) FCC areas were sampled annually in April. Soil nutrients and biomass accumulation was measured and compared. For weed suppression, five treatments were compared: till- green manure (GM), GM plus pre-emergence herbicide (GMH), and no-till after termination via crimp-mulch (CM), kill-mulch (KM) or mow-mulch (MM). In 2023, significantly higher fresh (514 t/ha) and dry (140 t/ha) biomass was added to the soil from densely and sparsely FCC areas, respectively. Weed suppression was better on GMH than GM for the first 6-8 weeks but reached an average of ≥ 67.5% when monitored 92 days after chickpea planting. Similarly, no-till planted chickpeas after CC terminations in 2021 suppressed weeds during early stages but not in 2022. In both years, it was not possible to harvest chickpeas after no-till due to overwhelming weed infestation. Although added organic matter was evident across all years, FCC alone did not significantly suppress weeds in 2022 and 2023. Slightly different results are anticipated with adjustments in termination timing and conditions favoring mulch establishment in 2024 growing season.
Sweetpotatoes (Ipomoea batatas L.) are among the most important food crops worldwide, but production in Missouri is limited. Weed competition, especially early in the growing season, is a major factor impacting sweetpotato yields. The objective of this study was to optimize early season weed control in sweetpotatoes using fall seeded cover crops and spring applied herbicides. Cover crops, cereal rye (Secale cereale L.) or winter wheat (Triticum aestivum L.), were seeded in the fall. Before sweetpotato transplanting the following spring, glyphosate was applied to terminate cover crop growth along with flumioxazin as a residual herbicide. In designated treatments, S-metolachlor was applied 3 weeks later to extend residual activity. A total of eight treatments, including an untreated control, and a second control consisting of herbicides followed by tillage and hand-weeding as Missouri standard practice, were arranged in a randomized complete block design with four replications. Sweetpotato ‘Beauregard’ slips were transplanted in early June 2023. By 4 weeks after transplanting (WATr), weed biomass in cover crop plus herbicide plots was reduced by 99.3% and 86.3% for broadleaf and grass weeds, respectively, compared to the untreated control. An orthogonal test found that sweetpotato production in plots that received winter wheat as cover crop resulted in a significantly higher yield compared to plots that received cereal rye as a cover crop. Winter wheat combined with flumioxazin applied PRE and S-metolachlor applied as an overlapping residual herbicide demonstrated the greatest yield among all treatments, resulting in over 200-fold greater yield compared to the untreated control. The Missouri standard practice, represented as the weed-free control, produced statistically the same yield as the best treatment. However, this was the most time-consuming and labor-intensive practice and would be challenging for commercial production. Collectively, our results suggest that sweetpotato production in Missouri should consider integration of cover crops and herbicides to allow strong establishment of sweetpotato vines early in the early growing season, and hence ensure higher profitability without intensive labor inputs.
The United States ranks second in strawberry production worldwide. Much of this production has been transitioned from perennial matted row to annual plasticulture production. However, in states like Indiana, growers are exploring a hybrid system: multi-year plasticulture production. In response, we explored cover crops for row-middle weed management in plasticulture strawberry production. In September 2022, we planted ‘Chandler’ strawberry plugs into white polyethylene-mulched rows at Lafayette and Vincennes, IN. We established five row-middle treatments: nontreated and wheat straw mulch controls and three cover crops (oats, cereal rye, and white clover). The oats were winter-killed, and the cereal rye was roller-crimped in mid-May of 2023. Data collected included percent cover crop and weed canopy (per 0.09 m2); frost-killed flowers, live flowers, and developed fruits per plant within 2 weeks after the last spring frost; and total fruit number and yield per plant. At 7 weeks after transplanting (WAP), the oats canopy (82%) was greater than that of cereal rye (61%) and white clover (22%) but less than straw mulch (96%). Weed canopy in the straw mulch and oats was 6%, less than the nontreated control (38%). At 27 and 35 WAP, the cereal rye canopy was 96% and 100%, respectively; while the other treatments had less than 85% and 74% coverage, respectively. At 27 WAP, cereal rye and oats at both sites and straw mulch at Vincennes had less weed canopy (< 7%) than the nontreated control (>63%). At 35 WAP, only cereal rye had no weed canopy. At Lafayette, all treatments had 15 frost-killed flowers per plant. At Vincennes, all treatments had 8 frost-killed flowers per plant, except cereal rye (2 frost-killed flowers per plant). There were no differences among treatments in the live flower count. The number of developed fruits at both sites was significantly greater with cereal rye (8 fruits per plant) compared to all the other treatments (≤ 5 fruit per plant). Total harvested fruit number and yield at Lafayette was 17 fruits per plant and 135 g per plant for all treatments. At Vincennes, cereal rye resulted in significantly greater fruit number (10 fruits per plant) and yield (99 g per plant) compared to all other treatments (≤ 5 fruit and ≤ 49 g per plant). This study demonstrated that cereal rye was the most effective choice for suppressing weeds while maintaining or increasing strawberry yield in the first year of a multi-year plasticulture production system.
Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus) are the two most troublesome pigweeds in crop production systems in the United States. These pigweeds just started to appear in the Pacific Northwest (PNW). A coordinated extension and outreach effort among land-grant universities (University of Idaho and Oregon State University), Amalgamated Sugar, other commodity commissions, and industry was launched to track Palmer amaranth and waterhemp in the PNW. In 2023, tissue samples were collected from pigweeds suspected to be Palmer amaranth and waterhemp and sent to Colorado State University for KASP genotyping test to confirm if the species were Palmer amaranth and waterhemp. The KASP test confirmed that the suspected pigweeds were Palmer amaranth and waterhemp. Since the majority of these pigweeds survived multiple applications of glyphosate, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene duplication analysis was conducted to confirm possible glyphosate resistance in the Palmer amaranth and waterhemp populations. About 70% (17 out of 23) of the Palmer amaranth tissue samples showed gene duplication of up to 184 EPSPS gene copies, indicative of glyphosate resistance. All three populations of waterhemp showed gene duplication of 5.7 to 9.2 EPSPS gene copies indicative of glyphosate resistance. The widespread glyphosate resistance in the samples collected suggests that Palmer amaranth and waterhemp being introduced into the PNW are coming from States where these weeds have developed resistance to multiple herbicide groups. This would have huge implications for weed control in vegetables and other crops in the PNW.
In recent years, doveweed [Murdannia nudiflora (L.) Brenan] has become a pressing concern in Florida and nearby regions due to its rapid expansion and challenging eradication. Despite being considered a warm-season annual broadleaf, its grass-like foliage often enables it going unnoticed within the canopy, especially at early growth stages. Such camouflage allows for quick proliferation and rapid invasion leading to dense mats outcompeting desired turfgrass sward. Limited reliable herbicides exist, and their efficacy declines once the plants get established. Hence, there is a demand for options capable of controlling mature populations. This study assessed the efficacy of mesotrione at 0.37 L ha-1 or 0.58 L ha-1, simazine at 1.10 L ha-1 or 1.83 L ha-1, and their combinations for the late-season control of established doveweed in bermudagrass ‘CR-01’ maintained as a golf course fairway or athletic field at West Florida Research and Education Center in Jay, FL. When used independently, mesotrione alone provided inconsistent control, never surpassing 50%, whereas simazine alone yielded a maximum control of 80%) was achieved within 2 to 6 weeks after the initial treatment, contingent upon the rate, with higher rates yielding a more rapid response. Moreover, the control remained persistent until the conclusion of the study. Severe phytotoxicity was evident in all mesotrione-containing treatments, yet the turf recovered to acceptable levels within 4 weeks following each application.
Targeted spray application technologies have the capacity to drastically reduce herbicide inputs but to be successful, performance of both machine vision (MV) based weed detection and actuator efficiency need to be optimized. This study assessed 1) the performance of spotted spurge recognition in ‘Latitude 36’ bermudagrass turf canopy using the You Only Look Once (YOLOv3) real-time multi-object detection algorithm, and 2) the impact of various nozzle densities on model efficiency and projected herbicide reduction under simulated conditions. The YOLOv3 model was trained and validated with a dataset of 1,191 images. The simulation design consisted of 4 grid matrix regimes (3 × 3, 6 × 6, 12 × 12, and 24 × 24) which would then correspond to 3, 6, 12, and 24 non-overlapping nozzles, respectively; covering a 50-cm wide band. Simulated efficiency testing was conducted using 50 images containing predictions (labels) generated with the trained YOLO model and, by applying each of the grid matrixes to individual images. The model resulted in prediction accuracy of a F1 Score of 0.62 precision of 0.65 and recall value of 0.60. Increased nozzle density (from 3 to 12) improved actuator precision and predicted herbicide-use efficiency with a reduction in false hits ratio from ~30% to 5%. The area required to ensure herbicide deposition to all spotted spurge detected within images was reduced to 18% resulting in ~80% herbicide savings compared to broadcast application. Slightly greater precision was predicted with 24 nozzles, but not statistically different from the 12-nozzle scenario. Using this turf/weed model as a basis, optimal actuator efficacy and herbicide savings would occur by increasing nozzle density from one to 12 nozzles with the context of a single band.
The economic significance of hemp (Cannabis sativa L.) as a source of grain, fiber, and flower is rising steadily. However, due to the lack of registered herbicides, hemp growers have limited weed management options. Slow-growing hemp varieties can be outcompeted by weeds for sunlight, water, and nutrients. Hence, easily adoptable integrated weed management (IWM) strategies are essential. Addressing these challenges necessitates novel approaches to identify quantitative phenotypes and explain the genetic basis of key weed-competitive traits. Plant height and canopy architecture may affect crop-weed competition. However, manually measuring these parameters is a time-consuming process. The PlantEye (PE) multispectral 3D scanner was selected as the high-throughput digital phenotyping technology for the evaluation of plant architecture. In this study, the suitability of digital phenotyping was evaluated at the Clemson University Coastal Research and Education Center to screen diverse hemp varieties with different plant habits. Digital plant biomass, plant height, and plant 3D-leaf area (including leaf area index, leaf angle, and light penetration) were periodically monitored. We performed a range of validation tests for morphological features (digital biomass and plant height). A significant correlation (P < 0.001) was observed between digital biomass and manually measured biomass (R = 0.89), as well as between digital height and manually measured height (R = 0.94), indicating the high precision and usefulness of 3D multispectral scanning in measuring morphological traits. Multispectral analyses used in this study are non-destructive, rapid techniques with minimal error and human interference, which have great potential for use in planning weed management.
Managing weeds is one of the most significant challenges, especially in organic vegetable production systems. Farmers control weeds in various ways, many of which can have negative environmental impacts. Cultivation is a common way many organic vegetable growers will manage weeds; however, it leads to decreased soil health properties. Hand weeding is extremely time-consuming and labor-intensive. Conventional herbicides have raised public concern for their impact on human health and the environment. Organic herbicide products are used as a burndown, post-emergence product but can be cost-prohibitive. In addition, there is a lack of current research comparing organic herbicide effectiveness on a range of common weed species. This study aimed to explore the efficacy of five Organic Materials Review Institute-approved organic herbicides. These products included citrus oil (Avenger®), ammonium nonanoate (AXXE®), acetic acid (Green Gobbler®), caprylic acid capric acid (HomePlate®), and clove oil cinnamon oil (Weed Zap®). Water was used as a control, and glyphosate (Ranger Pro®) was used as a positive control. Each herbicide was tested on six common weed species: Chenopodium album (common lambsquarters), Portulaca oleracea (common purslane), Setaria viridis (L.) Beauv. (green foxtail), Digitaria sanguinalis (L.) Scop. (large crabgrass), Amaranthus retroflexus (redroot pigweed), and Abutilon theophrasti (velvetleaf). Products were sprayed according to label recommendations using a calibrated spray chamber at the Iowa State University greenhouses. Each weed species, 10 plants per replication, was sprayed after reaching an average height of seven centimeters. Percent weed cover using digital image analysis software (Turf Analyzer) and percent visual injury was recorded. These data parameters were collected 24 hours, 3 days, 10 days, 17 days, and 21 days following herbicide application. Weed biomass was collected and dried 21 days after herbicide application for all species. AXXE® was a fast-acting herbicide on common lambsquarters, common purslane, redroot pigweed, and velvetleaf. These species showed over 85% injury three days after AXXE® application. Weed Zap® stunted the majority of examined weed species soon after application, but the injury effects were less significant 21 days after application. Visual injury assessments showed Avenger®, Green Gobbler®, HomePlate®, and Weed Zap® had no significant injury on green foxtail and large crabgrass 21 days after herbicide application. Results from this study provide growers with practical and applied data to make informed decisions regarding the use of organic herbicides.
Industrial hemp is receiving attention for its numerous benefits, particularly in the fiber industry. Weed competition is a primary concern for hemp cultivation causing reduced yields and inferior-quality fiber. However, little is known about herbicide application in hemp since a limited range of herbicides are available for hemp production. Therefore, a field study was conducted in 2023 to investigate the effect of different herbicides and application timings on weed suppression, crop injury, growth, and biomass yield of hemp. A randomized complete block design was conducted with six herbicide treatments including, early POST [2 weeks after planting (WAP)] and late POST (5 WAP) emergence applications of S-metolachlor, clopyralid, and ethalfluralin, with an untreated control to make comparisons. Plant stand showed no significant difference among treatments. Early POST herbicides application significantly reduced the weed biomass compared to untreated control at 7 WAP. By 10 WAP, weed biomass became comparable across treatments. At harvest, untreated control recorded comparatively higher weed biomass than early POST treatments and late POST ethalfluralin. Plant height remained non-significant among treatments until 10 WAP. At harvest, control showed no variation with late POST treatments but recorded an average 63% lower plant height than early POST applications. Treatments showed no significance for hemp biomass at 10 WAP. However, early POST S-metolachlor and ethalfluralin herbicides exhibited lower weed biomass and greater plant height, resulting in greater hemp biomass accumulation compared to untreated control at harvest. In conclusion, early POST S-metolachlor and ethalfluralin could be used as POSTemergence herbicides for hemp cultivation.
