Finger weeders were first developed in the 1950s and have since been widely adopted by farmers to improve physical weed control (PWC) within crop rows. Research on finger weeders has largely been comparative, with most studies identifying a top-performing weed control practice among various physical or chemical treatments. Weeding tool performance, however, is often highly variable, affected by tool design and adjustment, soil conditions, and both weed and crop species and size. Finger weeder operating settings have not been systematically tested to determine whether they could optimize tool performance. In this project, field and soil bin experiments examined the effects of finger weeder angle, spacing, and speed on weed control efficacy and weed/crop selectivity. Three finger weeder angles were tested: 108°, which removed soil near the crop; 90°, typical for most commercial tools; and 68°, which moved soil into the crop row. Three spacings and speeds were compared: fingers overlapping (−0.6 cm), touching (0 cm), or spaced apart (2.5 cm); and 4, 7, and 9 km h−1. In both the field and soil bin, finger weeders set at a 68° angle resulted in the greatest efficacy. Decreasing finger spacing and increasing speed improved efficacy in soil bin experiments, as expected, but spacing and speed effects were not detected in the field. The experimental soil bin system shows promise for PWC testing, possibly offering insights that could not be detected in more variable field conditions.

A diversity of management and environmental factors influence weed seedbank community composition, yet the conditions under which each of these factors is an important driver of the weed seedbank are poorly understood. To investigate this relationship, we used a series of univariate and multivariate analyses to test associations between soil health, nematode community composition parameters, and the composition of the weed seedbank at 59 agricultural sites in the Prince Edward Island Soil Quality Monitoring (PEI SQM) Network spanning a range of land-use intensities and using potato (Solanum tuberosum L.) production systems as a case study. Land-use intensity is a nonstandard term that refers to increasing agricultural activity, including tillage and use of synthetic inputs to sustain high crop yield. Sites were classified into low, medium, and high land-use intensity categories based on frequency of potato cultivation in the past 10 yr. A total of 36 different weed species were found across all sites, and while neither seedbank density nor species richness was influenced by land-use intensity, community assemblage was. Seedbank communities at low land-use intensity sites were largely associated with grass weeds and other weakly competitive species, positively correlated with soil CO2 respiration and nematode community richness and diversity, and negatively correlated with the carbon to nitrogen ratio. In contrast, seedbank communities at medium and high land-use intensity sites were similar and composed of many highly competitive weedy species and correlated with the frequency of potato in the rotation and soil N and K, two commonly used soil fertility inputs. The absence of common agricultural weed species at low land-use intensity sites filtered by soil edaphic factors and abundance of neutral species despite past history of annual cropping suggest that these sites are not refuges for these species and may present a template for the design of weed seed–suppressive soils.

Cover crops (CCs) are a component of the integrated weed management strategies for controlling herbicide-resistant weed biotypes. A field study was conducted at Kansas State University Agricultural Research Center near Hays, KS, from 2021 to 2024 to determine the effect of spring-planted CCs in combination with residual herbicide on weed suppression during fallow phase and subsequent wheat yield in a no-till winter wheat (Triticum aestivum L.)–grain sorghum [Sorghum bicolor (L.) Moench]–fallow rotation in the semiarid Central Great Plains (CGP). The study site had a natural seedbank of glyphosate-resistant (GR) kochia [Bassia scoparia (L.) A.J. Scott] and Palmer amaranth (Amaranthus palmeri S. Watson). A mixture of CCs (oats [Avena sativa L.]–barley [Hordeum vulgare L.]–spring peas [Pisum sativum L.]) was spring-planted in no-till sorghum stubbles and terminated at the oats heading stage. Four treatments were tested: (1) weedy fallow (no CC and no herbicide), (2) chemical fallow (no CC but glyphosate + flumioxazin/pyroxasulfone + dicamba), (3) CC terminated with glyphosate, and (4) CC terminated with glyphosate + flumioxazin/pyroxasulfone. Across 3 yr, CC at termination reduced total weed density by 78% to 99% and total weed biomass by 93% to 99% compared with weedy fallow. Weed suppression by the CC terminated with glyphosate plus flumioxazin/pyroxasulfone continued for at least 90 d with reduced total weed density of 52% to 80% and total weed biomass reduction by 70% compared with weedy fallow across 3 yr. No differences in subsequent wheat grain yield between CC treatments and chemical fallow were recorded in 2021 to 2022 and 2022 to 2023; however, in 2023 to 2024, chemical fallow and CC terminated with glyphosate + flumioxazin/pyroxasulfone had greater wheat yield than CC terminated with glyphosate only. These results suggest that integration of spring-planted CC with residual herbicide may help suppress GR B. scoparia and A. palmeri in the CGP.

Indaziflam (Rejuvra®), a preemergence herbicide first registered in vine and tree nut crops, was recently approved for applications to rangeland for winter annual grass control. Indaziflam controls cheatgrass (Bromus tectorum L.) for at least 3 yr, and control can extend into a fourth and fifth year; however, it is very difficult to find indaziflam residues in the soil 2 yr after application. Indaziflam could be absorbed by seeds still retained on the plant and on the soil surface in sufficient concentrations to stop establishment. To test this hypothesis, B. tectorum seeds and jointed goatgrass (Aegilops cylindrica Host) spikelets were treated with indaziflam and imazapic at rates from 5.4 to 175 g ai ha−1 using a greenhouse track sprayer delivering 187 L ha−1. Treated seeds were planted into field soil, and plants were allowed to grow for 21 d under greenhouse conditions. Growth was compared with growth of non-treated controls. In addition, a second set of treated seeds were exposed to rainfall 1 and 24 h after treatment and rainfall amounts ranging from 3 to 24 mm to determine whether rainfall impacted herbicide performance. Bromus tectorum was so sensitive to indaziflam that establishment was eliminated at all rates. Imazapic inhibited B. tectorum establishment with an ED90 of 67 g ai ha−1. Indaziflam effectively inhibits A. cylindrica establishment with an ED90 of 7.4 g ai ha−1 compared with imazapic with an ED50 of 175 g ai ha−1. Indaziflam’s impact on A. cylindrica establishment was not significantly impacted by rainfall, indicating that the herbicide was absorbed to the seed coat. These findings support the hypothesis that indaziflam’s long-term control could result from its ability to inhibit establishment of seeds retained in the canopy and those on the soil surface at the time of application.

Plants in the genera Astragalus and Oxytropis, collectively referred to as “locoweeds,” contain swainsonine, a toxic alkaloid synthesized by their fungal endophyte Alternaria sect. Undifilum. The ecological role of this endophyte across the mutualism–commensalism–parasitism continuum is unknown. We examined the fitness traits of Astragalus and Oxytropis species growing with and without the endophyte, in a 9-yr, common-garden experiment. Silky crazyweed (Oxytropis sericea Nutt.) and woolly loco (Astragalus mollissimus Torr.) plants germinated from seeds that naturally host the endophyte (E+) and with it mechanically removed (E−) were established in a common garden in southwest Montana. We measured mortality, gas exchange, flower and seed production, seed germination, and final biomass. Astragalus mollissimus plants grew as annuals under common-garden conditions regardless of endophyte status. Oxytropis sericea plants grew as perennials with survival unaffected by endophyte; however, E+ O. sericea plants produced slightly more reproductive stems, flowers per stem, and crown and stem biomass. Maternal effects detected in the parental generation disappeared in subsequent generations. Gas exchange, fecundity, and seed germination were unaffected by endophyte. Contrary to our initial hypothesis of mutualism, the endophyte did not improve host survival or fecundity, nor did we detect transgenerational effects. However, the endophyte did slightly increase the number of reproductive stems and flowers per stem and crown and stem mass in O. sericea, suggesting endophytic effects on carbohydrate biochemistry and pollination parameters should be examined. Lack of selection for or against endophyte-containing plants allows both nontoxic and toxic swainsonine-producing plants to persist in Astragalus and Oxytropis populations, posing a continued threat to grazing livestock.

Cattle (Bos spp.) grazing on weed–mixed forage biomass may potentially spread weed seeds, leading to plant invasions across pasturelands. Understanding the possibility and intensity of this spread is crucial for developing effective weed control methods in grazed areas. This research undertook an in vitro experiment to evaluate the germination and survival of five dominant weed species in the southern United States [Palmer amaranth (Amaranthus palmeri S. Watson), yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.], johnsongrass [Sorghum halepense (L.) Pers.], field bindweed (Convolvulus arvensis L.) and pitted morningglory (Ipomoea lacunosa L.)] upon incubation in rumen fluid for eight time periods (0, 4, 8, 12, 24, 24, 48, 72, and 96 h). For the 96-h treatment, a full Tilley and Terry procedure was applied after 48 h for stopping fermentation, followed by incubation for another 48 h simulating abomasum digestion. Seed germination, upon incubation, varied significantly among weed species, with I. lacunosa reaching zero germination after only 24 h of incubation, whereas A. palmeri and S. halepense retained up to 3% germination even after 96 h of incubation. The hard seed coats of A. palmeri and S. halepense likely made them highly resistant, whereas the I. lacunosa seed coat became easily permeable and ruptured under rumen fluid incubation. This suggests that cattle grazing can selectively affect seed distribution and invasiveness of weeds in grazed grasslands and rangelands, including the designated invasive and noxious weed species. As grazing is a significant component in animal husbandry, a major economic sector in the U.S. South, our research provides important insights into the potential role of grazing as a dispersal mechanism for some of the troublesome arable weeds in the United States. The results offer opportunities for devising customized feeding and grazing practices combined with timely removal of weeds in grazeable lands at the pre-flowering stage for effective containment of weeds.

Branched broomrape [Phelipanche ramosa (L.) Pomel], a parasitic weed with a broad host range, is a quarantine pest in California. Phelipanche ramosa plants can produce thousands of tiny seeds that are easily spread by farm equipment. Best management practices for reducing dispersal risk include physical cleaning and disinfestation of farm equipment, but data on the efficacy of sanitizers on weed seeds are limited. A three-phase study was undertaken during 2022 to 2023 to evaluate quaternary ammonium compound (QAC) sanitizer efficacy on P. ramosa seed germinability. First, several QAC ingredients were evaluated at various concentrations (0 to 2.5 g per 100 ml) and exposure durations (1, 3, and 5 min) to develop initial germination curves. Second, the experiments were conducted with three commercial QAC sanitizers (MG4-Quat [Mg4], Flo-Quat, and Cleaner QT-185) at the recommended dose (1% v/v) and a field-relevant exposure duration (1 min). The final experiments evaluated commercial QAC sanitizer efficacy in the presence of various debris types. The initial experiments showed that alkyl dimethyl benzyl ammonium chloride (ADAC), didecyl dimethyl ammonium bromide (DDAB), and didecyl dimethyl ammonium chloride (DDAC) effectively prevented P. ramosa germination, but the effective dose for a 50% reduction in P. ramosa seed germination ranged from 0.001% (g per 100 ml) at 10 min with DDAC to 0.35% (g per 100 ml) at 1 min with ADAC. While all three QAC sanitizers reduced seed germination 75% to 100% after a 1-min exposure to the recommended dose (1% v/v), this treatment did not affect seed germination in the presence of soil (100 mg ml−1) or fruit/plant tissue (40 mg ml−1). At higher concentrations of Mg4 (8% v/v), P. ramosa seed germination was reduced by 90% to 100%, even in the presence of soil and plant debris. This study demonstrates that while QAC sanitizers can reduce P. ramosa seed germinability, their efficacy is compromised in the presence of debris. Therefore, physical cleaning to reduce debris loads before QAC application is essential for reducing the risk of P. ramosa seed movement among fields on equipment.

Weed seeds are potential contaminants of composts derived from biowastes. We assessed the effect of steam treatment alone and in combination with composting on the mortality of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] seeds in a biowaste substrate consisting of a mixture of onion (Allium spp.) waste (60%), horse (Equus spp.) manure (20%), and wood shavings (20%). In the first study, seeds of six populations of E. crus-galli exposed to temperatures ranging from ca. 60 to 99 C followed by a 3-min residence time exhibited a decline in seed germination from approximately 25% to 0%. The E. crus-galli populations varied greatly in germinability and responded differently to high temperatures. Samples with lower germinability as assessed in controls were killed at lower temperatures than samples with higher initial germinability. However, to ensure an almost 100% kill of all seeds in the populations, a mean temperature of 100 C was necessary. In another study, seed germination was assessed after steaming the biowaste mixture to a mean temperature of about 60 C and subsequently composting. A short steaming period of the biowaste mixture at approximately 60 C before composting was unnecessary, as all composted seed samples, including the non-steamed control seeds, died during the composting process.

The mobility of a weed species is a strong determinant of the optimal management strategy, including whether area-wide management will be beneficial. In this paper, we examine the mobility and dispersal distances of flaxleaf fleabane [Conyza bonariensis (L.) Cronquist; syn.: Erigeron bonariensis L.], widely regarded as a highly mobile weed. We sampled individual weeds from two regions and sampled the same sites in the following season to conduct parentage analysis and assess intergenerational dispersal distances. We find high values of FIS across populations consistent with mostly self-fertilization, but also relatively high genotypic diversity, suggesting that outcrossing does occur at low rates. We find evidence for long-distance dispersal (more than 350 km) and detect dispersal distances of up to 71 km and 36 km within each of the two regions using parentage analysis. We also find high spatial genetic structure within the Riverina region, with sites in 2021 genetically very similar to sites in 2020, indicating that local dispersal may be a more important driver of population genetics than long-distance dispersal, perhaps due to the high rates of seed production and self-fertilization. Glyphosate resistance was not spatially structured in C. bonariensis in these regions, highlighting the role of movement, and significant proportions of susceptible plants were found in both regions. The high levels of mobility, including over potentially long distances, indicate that the value of control and preventing weed seed set is likely to extend beyond the farm and offer “area-wide” benefit.

Automatic precision herbicide application offers significant potential for reducing herbicide use in turfgrass weed management. However, developing accurate and reliable neural network models is crucial for achieving optimal precision weed control. The reported neural network models in previous research have been limited by specific geographic regions, weed species, and turfgrass management practices, restricting their broader applicability. The objective of this research was to evaluate the feasibility of deploying a single, robust model for weed classification across a diverse range of weed species, considering variations in species, ecotypes, densities, and growth stages in bermudagrass turfgrass systems across different regions in both China and the United States. Among the models tested, ResNeXt152 emerged as the top performer, demonstrating strong weed detection capabilities across 24 geographic locations and effectively identifying 14 weed species under varied conditions. Notably, the ResNeXt152 model achieved an F1 score and recall exceeding 0.99 across multiple testing scenarios, with a Matthews correlation coefficient (MCC) value surpassing 0.98, indicating its high effectiveness and reliability. These findings suggest that a single neural network model can reliably detect a wide range of weed species in diverse turf regimes, significantly reducing the costs associated with model training and confirming the feasibility of using one model for precision weed control across different turf settings and broad geographic regions.

Wild Mexican sunflower [Tithonia tubaeformis (Jacq.) Cass.] is one of the most important annual weeds for sugarcane (Saccharum spp. hybrid) and, to a lesser extent, for soybean [Glycine max (L.) Merr.] and bean (Phaseolus vulgaris L.) in the northwest of Argentina and some other countries. Currently, its management relies on chemical methods, and no information is available to develop alternative management methods. In the current study, we conducted laboratory germination assays in the presence of different conditions of light, temperature, and phytohormone (gibberellins and abscisic acid) concentrations, as well as fluridone, trinexapac-ethyl (TE), methyl viologen (MV), dry afterripening (DAR), cold stratification, and pericarp scarification. Likewise, a field experiment was carried out to assess the impact of various sugarcane crop residue amounts on seedling emergence. Darkness and constant temperatures (e.g., 20 C) reduced the germination of fresh seeds. The addition of TE, a gibberellic acid inhibitor, and abscisic acid reduced germination. In contrast, the addition of MV increased germination. Pericarp scarification and embryo excision stimulated germination, suggesting that the pericarp acts as a barrier to prevent germination. DAR did not promote germination. On the other hand, cold stratification enabled dormancy release, which in turn promoted germination when the stratified achenes germinated in light and at alternating temperatures of 20/30 C. Field experiments showed that increasing amounts of sugarcane crop residue were useful to reduce weed seedling emergence and biomass, probably by limiting the triggering effect of light and temperature alternation on seedling emergence. These findings provide information about the endogenous control of germination, which can be useful for developing a rational integrated management system for T. tubaeformis.

Weed diversity plays an important role in the functioning of agroecosystems. Moreover, a number of endangered/threatened plant species occur as weeds in arable fields and/or field boundaries. Agricultural intensification has imposed negative consequences on weed diversity in general, and the survival of the endangered/threatened plant species in particular. The objective of this review is to provide a theoretical framework for promoting cropland weed diversity through precision agriculture. A systematic review was conducted based on literature analysis, existing knowledge gaps, and current needs to identify a suitable approach for promoting cropland biodiversity while protecting crop yields. While nonchemical weed management methods and economic threshold–based approaches are touted to improve weed diversity, they are either ineffective or insufficient for this purpose; long-term economic consequences and the risk of weed adaptation are major concerns. A plant functional trait-based approach to promoting weed diversity, one that considers a plant’s ecosystem service potential and competitiveness with the crop, among other factors, has been proposed by researchers. This approach has tremendous potential for weed diversity conservation in commercial production systems, but field implementation has been limited thus far due to our inability to selectively control weeds at the individual-plant level. However, recent advancements in computer vision, machine learning, and site-specific weed management technologies may allow for the accurate elimination of unwanted plants while retaining the important ones. Here, we present a novel framework for the utilization of precision agriculture for the conservation of cropland weed diversity, including the protection of endangered/threatened plant species, while protecting crop yields. This approach is the first of its kind in which the control priority is ranked on an individual-plant basis, by integrating intrinsic weed trait values with field infestation characteristics, while management thresholds are tailored to specific goals and priorities.

Weed management practices in agroecosystems mainly rely on herbicide, mowing, or tillage. Electric weed control offers a novel alternative, with a range of commercially available products for weed management in agricultural environments. However, electrical weed control efficacy has not been effectively compared with conventional weed management practices. Further, electrical weed control products may have a fire risk, as highlighted but not assessed in prior studies. The current study evaluated an electric weed control machine (Zasso™ XPower) for weed management in four vineyard sites (in 2022 and 2023) in comparison to mowing and herbicide applications. Weed control tactics were applied in spring from budbreak to when shoots were approximately 10-cm long at EL growth stage 12. At an application speed of 1.1 to 1.4 km h−1, averaged across the four sites, electric weed control at 24 or 36 kW reduced weed biomass by 84% to 87%, herbicide reduced biomass by 88%, and mowing reduced biomass by 65%. An assessment of vine normalized difference vegetation index indicated no differences in grapevine (Vitis vinifera L.) canopy development (i.e., no evidence of damage to vines) after each treatment. To assess fire risk, the same machine was used at a separate field site to apply electric weed control to bare ground with varying levels of dry plant biomass. Electric weed control in the presence of completely dry plant biomass did pose a significant fire risk (average of 0.37 incidences of smoke/flame m−2). This technology is therefore not suitable for use in hot conditions where plant residue is dry. However, application in vineyards in the spring resulted in no evidence of fire. Our results, being the first of their kind, highlighted electric weed control as a potential alternative to chemical use that can be integrated into weed management programs in winter and spring within a Mediterranean climate.

Sterile oat [Avena sterilis L. ssp. ludoviciana (Durieu) Gillet & Magne] is rapidly proliferating in cereal fields across northeastern and northwestern Iran, underscoring the necessity of studying its ecology in these two distinct climates. A study was conducted to assess the impact of environmental factors on the germination of two native populations of A. sterilis. The germination responses of populations from Mashhad (northeastern Iran) and Tabriz (northwestern Iran) were evaluated under various treatments, including temperature, osmotic potential, NaCl concentration, and light/dark cycles. As the temperature increased and osmotic potential decreased—indicating heightened drought stress—the germination percentages of both populations declined. The Mashhad population exhibited the highest germination percentages, reaching 99% at 10 C and 100% at 15 C, both under 0 MPa osmotic potential. Conversely, the Tabriz population demonstrated its peak germination percentages at 15 C and 20 C, also under 0 MPa osmotic potential, with rates of 97% and 96%, respectively. The highest germination rates were observed in seeds from the Mashhad and Tabriz populations at 15 C, with osmotic potentials of 0 MPa and −0.3 MPa, yielding rates of 0.52 and 0.48 seeds d−1, respectively. The NaCl concentration required for 50% inhibition of seed germination was 4.76 dS m−1 for the Mashhad population and 3.90 dS m−1 for the Tabriz population. In both populations, the highest germination percentage was observed under a light/dark cycle of 10 h of light and 14 h of darkness. The differences in germination responses between the Mashhad and Tabriz populations can be attributed to local environmental adaptations. Variations in temperature, osmotic potential, and other climatic factors influence seed dormancy and germination traits, enabling populations to thrive in their specific habitats. These local adaptations contribute to differences in germination performance under various environmental conditions, ultimately affecting their potential spread across different regions.

Herbaceous perennials must annually rebuild the aboveground photosynthetic architecture from carbohydrates stored in crowns, rhizomes, and roots. Knowledge of carbohydrate utilization and storage can inform management decisions and improve control outcomes for invasive perennials. We monitored the nonstructural carbohydrates in a population of the hybrid Bohemian knotweed [Polygonum ×bohemicum (J. Chrtek & Chrtková) Zika & Jacobson [cuspidatum × sachalinense]; syn.: Fallopia ×bohemica (Chrtek and Chrtková) J.P. Bailey] and in Japanese knotweed [Polygonum cuspidatum Siebold & Zucc.; syn.: Fallopia japonica (Houtt.) Ronse Decr.]. Carbohydrate storage in crowns followed seasonal patterns typical of perennial herbaceous dicots corresponding to key phenological events. Starch was consistently the highest nonstructural carbohydrate present. Sucrose levels did not show a consistent inverse relationship with starch levels. Lateral distribution of starch in rhizomes and, more broadly, total nonstructural carbohydrates sampled before dormancy break showed higher levels in rhizomes compared with crowns. Total nonstructural carbohydrate levels in crowns reached seasonal lows at an estimated 22.6% of crown dry weight after accumulating 1,453.8 growing degree days (GDD) by the end of June, mainly due to depleted levels of stored starch, with the estimated minimum of 12.3% reached by 1,220.3 GDD accumulated by mid-June. Depletion corresponded to rapid development of vegetative canopy before entering the reproductive phase in August. Maximum starch accumulation in crowns followed complete senescence of aboveground tissues by mid- to late October. Removal of aboveground shoot biomass in late June to early July with removal of vegetation regrowth in early September before senescence would optimize the use of time and labor to deplete carbohydrate reserves. Additionally, foliar-applied systemic herbicide translocation to belowground tissue should be maximized with applications in late August through early fall to optimize downward translocation with assimilate movement to rebuild underground storage reserves. Fall applications should be made before loss of healthy leaf tissue, with the window for control typically ending by late September in Minnesota.

Vegetable production on plastic mulch in Georgia often combines fumigation, drip tape, raised beds, and plastic mulch, where three to five high-value crops are produced over 2 yr. With the elimination of methyl bromide as a soil fumigant, herbicides applied over plastic mulch before crop transplanting have become essential to maintain weed control. However, proper care must be taken to avoid crop damage from any herbicide residue. Experiments using simulated vegetable beds covered with totally impermeable film (TIF) were conducted to quantify the concentration of halosulfuron-methyl, glufosinate, glyphosate, S-metolachlor, and acetochlor remaining on the mulch and the amount of each herbicide that moved into the crop transplant hole when irrigation water was applied. With 0.63 cm of water irrigation, <2% of halosulfuron-methyl, glufosinate, and glyphosate remained on the surface of the TIF. In contrast, 91% and 15% of acetochlor remained on the TIF after irrigation with 0.63 and 1.27 cm of water, respectively. For S-metolachlor, 17% and 3% remained after the aforementioned irrigation volumes, respectively. The order of concentration detected in the transplant hole was equivalent to ranking the herbicides by water solubility: glyphosate > glufosinate > halosulfuron-methyl > S-metolachlor > acetochlor. All herbicide concentrations were below 1.0 mg ai/ae in the transplant hole regardless of irrigation volume. For halosulfuron, glyphosate, and glufosinate, these concentrations were equal to a 1.3 to 8.9 times the field use rate washing into the transplant hole. Acetochlor and S-metolachlor concentrations in the transplant hole were equivalent to 0.1× to 0.7× of field use rates, respectively. With further evaluations, the quantified herbicide concentrations in the transplant hole can be used to make changes to recommended rates and potentially create new options for growers to utilize.

Seed impact mills like the Redekop Seed Control Unit (SCU) and the integrated Harrington Seed Destructor (iHSD) have the potential to fit within the U.S. wheat (Triticum aestivum L.) production system, but they may be affected by changes in crop yield and harvest residue moisture, which can have an impact on chaff flow rate and chaff moisture, respectively. This research aimed to determine the seed kill of problematic weed species and how varying chaff flow rates and chaff moisture affect seed kill and horsepower draw of the SCU and the iHSD. Four different chaff flow rates were tested at 0.75, 1.5, 2.25, and 3.0 kg s−1, which span 0.5× to 2× of a combine’s standard throughput. Additionally, four chaff moisture contents were tested at 10.7%, 16.4%, 22.1%, and 27.8%, which span and exceed typical harvest conditions. Results indicated that >91% of all weed seeds of the tested species were killed by either mill. Seed kill decreased by 7.9% and 0.08% for every 1-kg increase in chaff flow rate for Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] and hairy vetch (Vicia villosa Roth), respectively, for the iHSD. Seed kill also decreased by 3.4% for every 1-kg increase in chaff flow rate for weedy L. perenne ssp. multiflorum for the SCU. Increasing chaff moisture resulted in seed kill decreasing by 0.43% and 0.015% for every 1% increase in chaff moisture for weedy L. perenne ssp. multiflorum and volunteer canola (Brassica napus L.), respectively, with the SCU. Both chaff flow rate and chaff moisture had a significant effect on horsepower draw for both mills compared with an empty mill. Despite the increase in horsepower draw and the decrease in seed kill, these data indicate the potential for seed impact mills to operate in less than ideal conditions while still providing seed kill rates >74%.

Residual herbicides are primarily degraded in the soil through microbial breakdown. Any practices that result in increased soil biological activity, such as cover cropping (between cash crop seasons), could lead to a reduced persistence of herbicides in the soil. Furthermore, cover crops can also interfere with herbicide fate by interception. Field trials were conducted between 2020 and 2023 in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation to investigate the influence of cover crop (cereal rye [Secale cereale L.] and crimson clover [Trifolium incarnatum L.]) use on soil enzyme activities (β-glucosidase [BG] and dehydrogenase [DHA]), its effect on the concentration of residual herbicides (sulfentrazone, S-metolachlor, cloransulam-methyl, atrazine, and mesotrione) in the soil, and the interception of herbicides by cover crop residue. The use of cover crops occasionally resulted in increased BG and DHA activities relative to the fallow treatment. However, even when there was an increase in the activity of these two enzymes, increased degradation of the residual herbicides was not observed. The initial concentrations of all residual herbicides in the soil were significantly reduced due to interception by cereal rye biomass. Nevertheless, significant reductions in early-season weed biomass were observed when residual herbicides were included in the tank mixture applied at cover crop termination relative to the application of glyphosate plus glufosinate. Results from this research suggest that the use of cereal rye or crimson clover as cover crops (between cash crop seasons) do not impact the persistence of residual herbicides in the soil or reduce their efficacy in controlling weeds early in the growing season.

The changing climate, land use, and agronomic practices are driving shifts in weed biology and management across Australia’s grain production systems. A stakeholder survey was conducted to identify key weed species, adaptations, and factors influencing future research priorities in three major cropping regions. The most problematic and adaptive species included rigid ryegrass (Lolium rigidum Gaudin), hairy fleabane [Conyza bonariensis (L.) Cronquist; syn.: Erigeron bonariensis L.], Bromus spp. (ripgut brome [Bromus diandrus Roth; syn.: Bromus rigidus Roth]), annual sowthistle (Sonchus oleraceus L.), wild radish (Raphanus raphanistrum L.), and feather fingergrass (Chloris virgata Sw.). These weeds also ranked high for future research focus. Observed adaptive traits included changes in dormancy and emergence patterns, shifts in phenology, and a shift toward year-round growth driven by warmer winters and increased summer rainfall. Regional responses varied slightly, with soil and crop management practices ranked as the primary driver of changing weed biology (88%), followed by climatic factors (56%), while soil factors (13%) were not considered to be significant. Participants in the Northern region highlighted climate change (67%) as a major driver, while those in the Western region emphasized management practices (95%) and soil-related factors (32%). Sixty percent of participants noted that climatic changes were introducing new weeds, and 69% believed that changing weed biology was reducing control efficacy. National research priorities included understanding weed emergence dynamics (73%), effects of climate on herbicide efficacy (71%), and better understanding of weed ecology (68%). These findings highlight the trends in weed evolution and need for future research on changing weed biology and adaptive management strategies. Surveys of agronomists, farm advisors, researchers, and farmers provide a cost-effective method to monitor new weed adaptations. Refining survey methodologies and enhancing field data collection could improve the ability to track and manage weed adaptations to shifts in climate and management practices.

Combine modifications for harvest weed seed control like the Redekop Seed Control Unit (SCU) and the integrated Harrington Seed Destructor (iHSD) have been successfully used to kill problematic weed seeds in small grain production in Australia. These seed impact mills could have a fit in U.S. soybean [Glycine max (L.) Merr.] production. Testing the seed kill rate of problematic weed species in soybean is important for confirming the efficacy of the mills. Additionally, the mills may be affected by changes in crop yield and harvest residue moisture, which can have an impact on chaff flow rate and chaff moisture, respectively. This research aimed at determining the seed kill percent for problematic weeds and how varying chaff flow rates and chaff moisture content in soybean chaff affect the seed kill rate and horsepower draw of two different impact mills, the Redekop SCU and the iHSD. All testing was conducted using stationary test stands. Chaff flow rate and chaff moisture levels tested ranged from 0.5× to 2× standard combine throughput and 11.7% to 28.6% moisture, respectively. All tested species were killed at >98% by both mills. Increasing chaff flow rate resulted in a decrease in seed kill for all tested species with the iHSD and only common ragweed (Ambrosia artemisiifolia L.) with the Redekop SCU. Increasing chaff moisture only resulted in a decrease in seed kill for Palmer amaranth (Amaranthus palmeri S. Watson) with the iHSD. Data evaluating the horsepower needed to power the mills also indicated that chaff flow rate and chaff moisture resulted in a significant increase in horsepower draw. With generally high kill rates (>98%) and the ability to kill weed seeds at >98% in less than ideal harvest conditions (i.e., high-moisture chaff), seed impact mills could be used in soybean production to reduce weed seed inputs into the soil seedbank during harvest.