Site-specific weed management (on the scale of a few meters or less) has the potential to greatly reduce pesticide use and its associated environmental and economic costs. A prerequisite for site-specific weed management is the availability of accurate maps of the weed population that can be generated quickly and cheaply. Improvements and cost reductions in unmanned aerial vehicles (UAVs) and camera technology mean these tools are now readily available for agricultural use. We used UAVs to collect aerial images captured in both RGB and multispectral formats of 12 cereal fields (wheat [Triticum aestivum L.] and barley [Hordeum vulgare L.]) across eastern England. These data were used to train machine learning models to generate prediction maps of locations of black-grass (Alopecurus myosuroides Huds.), a prolific weed in UK cereal fields. We tested machine learning and data set resampling methods to obtain the most accurate system for predicting the presence and absence of weeds in new out-of-sample fields. The accuracy of the system in predicting the absence of A. myosuroides is 69% and its presence above 5 g in weight with 77% accuracy in new out-of-sample fields. This system generates prediction maps that can be used by either agricultural machinery or autonomous robotic platforms for precision weed management. Improvements to the accuracy can be made by increasing the number of fields and samples in the data set and the length of time over which data are collected to gather data across the entire growing season.

Mitotic-inhibiting herbicides, like prodiamine and dithiopyr, are used to control annual bluegrass (Poa annua L.) preemergence in managed turfgrass; however, resistance to mitotic-inhibiting herbicides has evolved due to repeated applications of herbicide from a single mechanism of action. Three suspected resistant populations (R1, R2, and R3) were collected in Alabama and Florida and screened for resistance to prodiamine. Part of the α-tubulin gene was sequenced for known target-site mutations. Target-site mutations were reported in all three R populations, with each containing an amino acid substitution at position 239 from threonine to isoleucine (Thr-239-Ile). Previous research has indicated that the Thr-239-Ile mutation confers resistance to dinitroaniline herbicides in other species. Dose–response screens using prodiamine and dithiopyr were conducted and I50 values were calculated for R1, R2, and R3 using regression models based on seedling emergence. For prodiamine, I50 values for R1, R2, and R3 were 35.3, 502.7, and 91.5 g ai ha−1, respectively, resulting in 2.9-, 41.9-, and 7.6-fold resistance, respectively, when compared with a susceptible (S) population. For dithiopyr, I50 values for R1, R2, and R3 were 154.0, 114.2, and 190.1 g ai ha−1, respectively, resulting in 3.6-, 2.7-, and 4.5-fold resistance, respectively, when compared with an S population. When comparing I90 values with the highest labeled use rates, R2 had a 2.9-fold level of resistance to prodiamine, and R1, R2, and R3 had a 2.4-, 2.0-, and 3.2-fold levels of resistance to dithiopyr, respectively. This is the first report of a variable response in P. annua to prodiamine despite each R population possessing the same mutation.

Public concern regarding the use of herbicides in urban areas (e.g., golf courses, parks, lawns) is increasing. Thus, there is a need for alternative methods for weed control that are safe for the public, effective against weeds, and yet selective to turfgrass and other desirable species. New molecular tools such as ribonucleic acid interference (RNAi) have the potential to meet all those requirements, but before these technologies can be implemented, it is critical to understand the perceptions of key stakeholders to facilitate adoption as well as regulatory processes. With this in mind, turfgrass system managers, such as golf course superintendents and lawn care providers, were surveyed to gain insight into the perception and potential adoption of RNAi technology for weed management. Based on survey results, turfgrass managers believe that cost of weed management and time spent managing weeds are the main challenges faced in their fields. When considering new weed management tools, survey respondents were most concerned about cost, efficacy, and efficiency of a new product. Survey respondents were also optimistic toward RNAi for weed management and would either use this technology in their own fields or be willing to conduct research to develop RNAi herbicides. Although respondents believed that the general public would have some concerns about this technology, they did not believe this to be the most important factor for them when choosing new weed management tools. The need for new herbicides to balance weed control challenges and public demands is a central factor for turfgrass managers’ willingness to use RNAi-based weed control in turfgrass systems. They believe their clientele will be accepting of RNAi tools, although further research is needed to investigate how a wider range of stakeholders perceive RNAi tools for turfgrass management more broadly.

Growers have been experimenting with cover crop termination timings to maximize weed suppression and potentially reduce herbicide inputs in soybean [Glycine max (L.) Merr.]. A field study was replicated three times from 2018 through 2021 in South Charleston, OH, to evaluate different management strategies involving a cereal rye (Secale cereale L.) cover crop. The objectives were to determine the effects of cereal rye seeding rate (0, 50, and 100 kg ha−1), management program (preplant, postplant, and delayed), and soybean residual herbicide (flumioxazin + chlorimuron ethyl and no herbicide) on cover crop, weed, and soybean parameters. The preplant program consisted of cereal rye terminated 7 d before planting (DBP) + a postemergence application. The postplant program consisted of cereal rye terminated 7 d after planting (DAP) + a postemergence application. In the delayed program, saflufenacil was applied in April and cereal rye was terminated 21 DAP, and there was no postemergence application. Giant foxtail (Setaria faberi Herrm.) density was reduced by the presence of cereal rye, averaged over other factors, regardless of seeding rate. Cereal rye seeding rate did not affect giant ragweed (Ambrosia trifida L.) density. The delayed management program was generally associated with the lowest weed density, but weed density was often similar in the postplant program. Setaria faberi density was lower in treatments that included a residual herbicide. Residual soybean herbicide use did not affect density of A. trifida. Terminating cereal rye after soybean planting resulted in increased soybean yield in 2019 and reduced yield in 2020, compared with preplant rye termination. These data suggest that adjusting the cereal rye management program may have a greater effect on weed suppression than adjustments to seeding rate. Delaying termination of cereal rye can aid in the suppression of weeds, but a comprehensive herbicide program was necessary to provide adequate (>85%) weed control.

Waterhemp (Amaranthus tuberculatus [Moq.] Sauer) escapes are common in midwestern U.S. soybean [Glycine max (L.) Merr.] fields due to the continued rise in herbicide-resistant (HR) populations. In a conventional harvesting system, weed seeds are harvested with the crop grain and spread back on to the field. Harvest weed seed control methods such as chaff lining concentrate weed seed-bearing crop and weed chaff into a narrow row (chaff line). These chaff lines (30- to 50-cm wide) are undisturbed the following growing seasons, under the assumption that the chaff line creates an environment less favorable for weed seed germination and survival. Field experiments were conducted in a soybean–corn (Zea mays L.) rotation in 2020 and 2021 in Ames, IA, and Roland, IA, to quantify the effectiveness of chaff lining for managing A. tuberculatus seeds. About 70% of the A. tuberculatus seeds were retained on the mother plant at soybean harvest in 2020. The chaff lining system concentrated more than 99% of the A. tuberculatus seeds exiting the combine into the chaff line. Although A. tuberculatus population density in 2021 was 76% higher inside the chaff line than outside the chaff line, A. tuberculatus aboveground biomass was 63% lower inside the chaff line than outside the chaff line at 12 wk after corn planting. Similarly, A. tuberculatus inside the chaff line had delayed emergence compared with A. tuberculatus outside the chaff line. Application of preemergence herbicides in corn inside the chaff line delayed A. tuberculatus emergence by more than 2 wk compared with A. tuberculatus outside the chaff line. Additionally, a follow-up postemergence herbicide application in corn was needed only inside the chaff line to manage A. tuberculatus, suggesting the possibility of lower overall herbicide use. These results support implementing chaff lining in soybean-based crop systems of the U.S. Midwest to help manage HR A. tuberculatus seedbanks.

Weed interference is a major factor that reduces peanut (Arachis hypogaea L.) yield in the United States. Peanut growers rely heavily on herbicides for weed control. Although effective, herbicides are not a complete solution to the complex challenge that weeds present. Therefore, the use of nonchemical weed management options is essential. The literature on weed research in peanut in the past 53 yr in the United States was reviewed to assess the achievements and identify current research gaps and prospects for nonchemical weed management for future research. More than half (79%) of the published studies were from the southeastern United States. Most studies (88%) focused on weed management, while fewer studies (12%) addressed weed distribution, ecology, and competitive mechanisms. Broadleaf weeds were the most frequently studied weed species (60%), whereas only 23% and 19% of the published studies were relevant to grasses and Cyperus spp., respectively. Seventy-two percent of the published studies focused on curative measures using herbicides. Nonchemical methods using mechanical (5%) and preventive (13%) measures that influence crop competition and reduce the buildup of the weed seedbank, seedling recruitment, and weed seed production have received less attention. In most studies, the preventive weed management measures provided weed suppression and reduced weed competition but were not effective enough to reduce the need for herbicides to protect peanut yield. Therefore, future research should focus on developing integrated weed management strategies based on multiple preventive measures rather than one preventive measure combined with one or more curative measures. We recommend that research on mechanical weed management should focus on the role of cultivation when integrated with currently available herbicides. For successful weed management with lasting outcomes, the dominant weed communities of specific target locations should be addressed within the context of climate change and emerging constraints rather than focusing on single problematic species.

We conducted an online survey of weed scientists in the United States and Canada to (1) identify research topics perceived to be important for advancing weed science in the next 5 to 10 years and (2) gain insight into potential gaps in current expertise and funding sources needed to address those priorities. Respondents were asked to prioritize nine broad research areas, as well as 5 to 10 subcategories within each of the broad areas. We received 475 responses, with the majority affiliated with academic institutions (55%) and working in cash crop (agronomic or horticultural) study systems (69%). Results from this survey provide valuable discussion points for policy makers, funding agencies, and academic institutions when allocating resources for weed science research. Notably, our survey reveals a strong prioritization of Cultural and Preventative Weed Management (CPWM) as well as the emerging area of Precision Weed Management and Robotics (PWMR). Although Herbicides remain a high-priority research area, continuing challenges necessitating integrated, nonchemical tactics (e.g., herbicide resistance) and emerging opportunities (e.g., robotics) are reflected in our survey results. Despite previous calls for greater understanding and application of weed biology and ecology in weed research, as well as recent calls for greater integration of social science perspectives to address weed management challenges, these areas were ranked considerably lower than those focused more directly on weed management. Our survey also identified a potential mismatch between research priorities and expertise in several areas, including CPWM, PWMR, and Weed Genomics, suggesting that these topics should be prime targets for expanded training and collaboration. Finally, our survey suggests an increasing reliance on private sector funding for research, raising concerns about our discipline’s capacity to address important research priority areas that lack clear private sector incentives for investment.

North African knapweed (Centaurea diluta Aiton), cornflower (Centaurea cyanus L.), corn marigold [Glebionis segetum (L.) Fourr.], rigid ryegrass (Lolium rigidum Gaudin), and corn poppy (Papaver rhoeas L.) are weeds of economic importance in the Iberian Peninsula, particularly due to limited herbicide options for effective control. For this reason, information about their seedling emergence has become critical to develop effective integrated management strategies and better time control actions. The aims of this study were to evaluate the effect of seed burial depth and soil disturbance on the emergence of these weed species. Two pot experiments were carried out to (1) quantify seedling emergence at three burial depths (2, 5, and 9 cm) and (2) characterize seedling emergence in response to different frequencies and timings of soil disturbance. Burial depth limited the emergence of G. segetum and P. rhoeas at 5 and 9 cm, respectively; while seedling emergence of C. diluta, C. cyanus, and L. rigidum were reduced by 92%, 90%, and 67% at 9 cm compared with 2 cm, respectively. Two or more sequential soil disturbance events increased total seedling emergence of C. diluta, P. rhoeas, and G. segetum compared with single events, while L. rigidum did not respond to repeated soil disturbance. These results suggest that turning the soil to bury weed seeds down to 5 cm or deeper would be a very effective method to control G. segetum and P. rhoeas and moderately effective to control C. cyanus. Also, the use of a stale seedbed would have some efficacy to reduce P. rhoeas and C. diluta weed pressure within the crop. This study illustrates how differences among species in seedling emergence in response to soil depth and disturbance can determine distinct emergence patterns ultimately influencing the selection of weed control tools and timing.

Palmer amaranth (Amaranthus palmeri S. Watson) is a troublesome weed in several cropping systems in the United States. The evolution of resistance to multiple herbicides is a challenge for the management of this weed. Recently, we reported metabolic resistance to 2,4-D possibly mediated by cytochrome P450 (P450) activity in a six-way-resistant A. palmeri population (KCTR). Plant growth temperature can influence the herbicide efficacy and level of resistance. The effect of temperature on 2,4-D resistance in A. palmeri is unknown. In the present research, we investigated the response of KCTR and a known susceptible (MSS) A. palmeri response to 2,4-D grown under low-temperature (LT, 24/14 C, day/night [d/n]) or high-temperature (HT, 34/24 C, d/n) regimes. When MSS and KCTR plants were 8- to 10-cm tall, they were treated with 0, 140, 280, 560 (field recommended dose), 1,120, and 2,240 g ai ha−1 of 2,4-D. Further, 8- to 10-cm-tall MSS and KCTR plants grown at LT and HT were also treated with [14C]2,4-D to assess the metabolism of 2,4-D at LT and HT. The results of dose–response experiments suggest that KCTR A. palmeri exhibits 23 times more resistance to 2,4-D at HT than MSS. Nonetheless, at LT, the resistance to 2,4-D in KCTR was only 2-fold higher than in MSS. Importantly, there was enhanced metabolism of 2,4-D in both KCTR and MSS A. palmeri at HT compared with LT. Further, treatment with the P450 inhibitor malathion, followed by 2,4-D increased the susceptibility of KCTR at HT. Overall, rapid metabolism of 2,4-D increased KCTR resistance to 2,4-D at HT compared with LT. Therefore, the application of 2,4-D when temperatures are cooler can improve control of 2,4-D–resistant A. palmeri.

Weeds are a fundamental component of agroecosystems and, if not appropriately managed, can cause severe crop yield losses. New perspectives on weed management are required, because current approaches, such as herbicide application or soil tillage, have significant environmental and agronomic drawbacks. We propose the concept of “neutral weed communities,” which are weed communities that coexist with crops and do not negatively affect crop yield and quality compared with weed-free conditions. Management practices that promote neutral weed communities can enable reduced use of herbicides and soil tillage while enhancing ecosystem services and biodiversity. We report scientific evidence of neutral weed communities and survey ecological explanations for why different weed communities have different effects on crop production. We also propose two weed management approaches for attaining neutral weed communities. The first approach aims to maximize weed biodiversity using traditional approaches such as cropping system diversification and integrated weed management. Higher weed biodiversity is associated with lower dominance of competitive weed species that reduce crop yield. The second approach relies on modern tools such as robots and biotechnology to manipulate the density of specific weed species. This approach can remove highly problematic species and minimize niche overlap between the weeds and crops. Given the complexity of interactions among crops, weeds, and other components of the agroecosystem, we highlight the need for multidisciplinary research to illuminate mechanisms that determine the neutrality of weed communities.

The current assays to confirm herbicide resistance can be time- and labor-intensive (dose–response) or require a skill set/technical equipment (genetic sequencing). Stakeholders could benefit from a rapid assay to confirm herbicide-resistant weeds to ensure sustainable crop production. Because protoporphyrinogen oxidase (PPO)-inhibiting herbicides rapidly interfere with chlorophyll production/integrity; we propose a new, rapid assay utilizing spectral reflectance to confirm resistance. Leaf disks were excised from two PPO-inhibiting herbicide-resistant (target-site [TSR] and non–target site [NTSR]) and herbicide-susceptible redroot pigweed (Amaranthus retroflexus L.) populations and placed into a 24-well plate containing different concentrations (0 to 10 mM) of fomesafen for 48 h. A multispectral sensor captured images from the red (668 nm), green (560 nm), blue (475 nm), and red edge (717 nm) wavebands after a 48-h incubation period. The green leaf index (GLI) was utilized to determine spectral reflectance ratios of the treated leaf disks. Clear differences of spectral reflectance were observed in the red edge waveband for all populations treated with the 10 mM concentration in the dose–response assays. Differences of spectral reflectance were observed for the NTSR population compared with the TSR and susceptible populations treated with the 10 mM concentration in the green waveband and the GLI in the dose–response assay. Leaf disks from the aforementioned A. retroflexus populations and two additional susceptible populations were subjected to a similar assay with the discriminating concentration (10 mM). Spectral reflectance was different between the PPO-inhibiting herbicide-resistant and herbicide-susceptible populations in the red, blue, and green wavebands. Spectral reflectance was not distinctive between the populations in the red edge waveband and the GLI. The results provide a basis for rapidly (∼48 h) detecting PPO-inhibiting herbicide-resistant A. retroflexus via spectral reflectance. Discrimination between TSR and NTSR populations was possible only in the dose–response assay, but the assay still has utility in distinguishing herbicide-resistant plants from herbicide-susceptible plants.

Damage to non–dicamba resistant (non-DR) soybean [Glycine max (L.) Merr.] has been frequent in geographies where dicamba-resistant (DR) soybean and cotton (Gossypium hirsutum L.) have been grown and sprayed with the herbicide in recent years. Off-target movement field trials were conducted in northwest Arkansas to determine the relationship between dicamba concentration in the air and the extent of symptomology on non-DR soybean. Additionally, the frequency and concentration of dicamba in air samples at two locations in eastern Arkansas and environmental conditions that impacted the detection of the herbicide in air samples were evaluated. Treatment applications included dicamba at 560 g ae ha−1 (1X rate), glyphosate at 860 g ae ha−1, and particle drift retardant at 1% v/v applied to 0.37-ha fields with varying degrees of vegetation. The relationship between dicamba concentration in air samples and non-DR soybean response to the herbicide was more predictive with visible injury (generalized R 2 = 0.82) than height reduction (generalized R 2 = 0.43). The predicted dicamba air concentration resulting in 10% injury to soybean was 1.60 ng m−3 d−1 for a single exposure. The predicted concentration from a single exposure to dicamba resulting in a 10% height reduction was 3.78 ng m−3 d−1. Dicamba was frequently detected in eastern Arkansas, and daily detections above 1.60 ng m−3 occurred 17 times in the period sampled. The maximum concentration of dicamba recorded was 7.96 ng m−3 d−1, while dicamba concentrations at Marianna and Keiser, AR, were ≥1 ng m−3 d−1 in six samples collected in 2020 and 22 samples in 2021. Dicamba was detected consistently in air samples collected, indicating high usage in the region and the potential for soybean damage over an extended period. More research is needed to quantify the plant absorption rate of volatile dicamba and to evaluate the impact of multiple exposures of gaseous dicamba on non-targeted plant species.

The mitotic-inhibiting herbicide pronamide controls susceptible annual bluegrass (Poa annua L.) pre- and postemergence, but in some resistant populations, postemergence activity is compromised, hypothetically due to a target-site mutation, lack of root uptake, or an unknown resistance mechanism. Three suspected pronamide-resistant (LH-R, SC-R, and SL-R) and two pronamide-susceptible (BS-S and HH-S) populations were collected from Mississippi golf courses. Dose–response experiments were conducted to confirm and quantify pronamide resistance, as well as resistance to flazasulfuron and simazine. Target sites known to confer resistance to mitotic-inhibiting herbicides were sequenced, as were target sites for herbicides inhibiting acetolactate synthase (ALS) and photosystem II (PSII). Pronamide absorption and translocation were investigated following foliar and soil applications. Dose–response experiments confirmed pronamide resistance of LH-R, SC-R, and SL-R populations, as well as instances of multiple resistance to ALS- and PSII-inhibiting herbicides. Sequencing of the α-tubulin gene confirmed the presence of a mutation that substituted isoleucine for threonine at position 239 (Thr-239-Ile) in LH-R, SC-R, SL-R, and BS-S populations. Foliar application experiments failed to identify differences in pronamide absorption and translocation between the five populations, regardless of harvest time. All populations had limited basipetal translocation—only 3% to 13% of the absorbed pronamide—across harvest times. Soil application experiments revealed that pronamide translocation was similar between SC-R, SL-R, and both susceptible populations across harvest times. The LH-R population translocated less soil-applied pronamide than susceptible populations at 24, 72, and 168 h after treatment, suggesting that reduced acropetal translocation may contribute to pronamide resistance. This study reports three new pronamide-resistant populations, two of which are resistant to two modes of action (MOAs), and one of which is resistant to three MOAs. Results suggest that both target site– and translocation-based mechanisms may be associated with pronamide resistance. Further research is needed to confirm the link between pronamide resistance and the Thr-239-Ile mutation of the α-tubulin gene.

In the transition zone, turfgrass managers generally utilize the dormancy period of warm-season turfgrass to apply herbicides for managing winter annual weeds. Although this weed control strategy is common in bermudagrass [Cynodon dactylon (L.) Pers.], it has been less adopted in zoysiagrass (Zoysia spp.) due to variable turfgrass injury during post-dormancy transition. Previous research reported that air temperature could affect weed control and crop safety from herbicides. Growth-chamber studies were conducted to evaluate zoysiagrass response to glyphosate and glufosinate as influenced by three different temperature regimes during and after treatment. A field research study was conducted at four site-years to assess the influence of variable heat-unit accumulation on zoysiagrass response to seven herbicides. In the growth-chamber study, glufosinate injured zoysiagrass more than glyphosate and reduced time to reach 50% green cover reduction, regardless of the rate, when incubated for 7 d under different temperature levels. When green zoysiagrass sprigs were incubated for 7 d at 10 C, the rate of green cover reduction was slowed for both herbicides; however, green cover was rapidly reduced under 27 C. After treated zoysiagrass plugs having 5% green cover were incubated at 10 C for 14 d, glyphosate-treated plugs reached 50% green cover in 22 d, similar to nontreated plugs but less than the 70 d required for glufosinate-treated plugs. Zoysiagrass response to glyphosate was temperature dependent, but glufosinate injured zoysiagrass unacceptably regardless of temperature regime. Diquat, flumioxazin, glufosinate, and metsulfuron + rimsulfuron injured zoysiagrass at 200 or 300 growing-degree days at base 5 C (GDD5C) application timings, but foramsulfuron and oxadiazon did not injure zoysiagrass regardless of GDD5C. The relationship of leaf density to green turf cover is dependent on zoysiagrass mowing height, and both metrics are reduced by injurious herbicides. Research indicates that glufosinate injures zoysiagrass more than glyphosate, and the speed and magnitude of herbicide injury generally increase with temperature.

Cover crops (CCs) have shown great potential for suppressing annual weeds within agronomic cropping systems across the United States. However, the weed suppressive potential of CCs may be moderated by environmental and management factors that are specific to certain geographic areas and their associated characteristics. This may be particularly true within the U.S. Southeast, where higher mean annual temperature and precipitation generate favorable conditions for both CC and weed growth. To understand the effects of this regional context on CCs and weeds, a meta-analysis examining paired comparisons of weed biomass and/or weed density under CC and bare ground conditions from studies conducted within the Southeast was conducted. Data were identified and extracted from 28 journal articles in which weed biomass and/or weed density were measured along with cash crop yield data, if they were provided. Fourteen studies provided 142 comparisons for weed biomass; 23 studies provided 139 comparisons for weed density; and 22 studies, pooled over both weed response variables, provided 144 comparisons for cash crop yield. CCs had a negative effect on weed density (P = 0.0016) but no effect on either weed biomass (P = 0.16) or cash crop yield (P = 0.88). The mean relative reduction in weed density under CCs was 44%. Subsequent analyses indicated that CC biomass was the key factor associated with this reduction. Weed density suppression was linearly related to CC biomass; a 50% decrease in weed density was associated with 6,600 kg ha−1 of CC biomass. Edaphic, geographic, and other management factors had no bearing on this suppressive effect. This highlights the importance of generating adequate CC biomass if weed suppression is the primary objective of CC use and the potential for CCs to reduce weed density over diverse soil, climate, and farm management conditions.

Protoporphyrinogen oxidase (PPO)-inhibiting herbicides remain an important and useful chemistry 60 yr after their first introduction. In this review, based on topics introduced at the Weed Science Society of America 2021 symposium titled “A History, Overview, and Plan of Action on PPO Inhibiting Herbicides,” we discuss the current state of PPO-inhibiting herbicides. Renewed interest in the PPO-inhibiting herbicides in recent years, due to increased use and increased cases of resistance, has led to refinements in knowledge regarding the mechanism of action of PPO inhibitors. Herein we discuss the importance of the two isoforms of PPO in plants, compile a current knowledge of target-site resistance mechanisms, examine non–target site resistance cases, and review crop selectivity mechanisms. Consistent and reproducible greenhouse screening and target-site mutation assays are necessary to effectively study and compare PPO-inhibitor resistance cases. To this end, we cover best practices in screening to accurately identify resistance ratios and properly interpret common screens for point mutations. The future of effective and sustainable PPO-inhibitor use relies on development of new chemistries that maintain activity on resistant biotypes and the promotion of responsible stewardship of PPO inhibitors both new and old. We present the biorational design of the new PPO inhibitor trifludimoxazin to highlight the future of PPO-inhibitor development and discuss the elements of sustainable weed control programs using PPO inhibitors, as well as how responsible stewardship can be incentivized. The sustained use of PPO inhibitors in future agriculture relies on the effective and timely communication from mode of action and resistance research to agronomists, Extension workers, and farmers.

Development of integrated weed management strategies requires knowledge of weed emergence timing and patterns, which are regulated primarily by water and thermal requirements for seed germination. Laboratory experiments were conducted in fall 2017 to fall 2018 to quantify the effect of osmotic potential and temperature on germination of 44 kochia [Bassia scoparia (L.) A.J. Scott] populations under controlled conditions. Bassia scoparia populations were collected in fall 2016 from northern (near Huntley, MT, and Powell, WY) and southern (near Lingle, WY, and Scottsbluff, NE) regions of the U.S. Great Plains. Ten osmotic potentials from 0 to −2.1 MPa and eight constant temperatures from 4 to 26 C were evaluated. Response of B. scoparia populations to osmotic potential did not differ between the northern and southern regions. At an osmotic potential of 0 MPa, all B. scoparia populations had greater than 98% germination, and the time to achieve 50% germination (t 50) was less than 1 d. At −1.6 MPa, 25% of seeds of all B. scoparia populations germinated. Osmotic potentials of −0.85 and −1.9 MPa reduced B. scoparia germination by 10% and 90%, respectively. Regardless of temperature regime, all populations exhibited greater than 88% germination. The germination rate was highest at temperatures between 15 to 26 C and did not differ between populations from northern versus southern regions. At this temperature range, all populations had a t 50 of less than 1 d. However, at 4 C, B. scoparia populations from the northern region had a higher germination rate (5 h) and cumulative germination (7%) than populations from the southern region. Overall, these results indicate a wide range of optimum temperatures and osmotic potential requirements for B. scoparia germination.

Field experiments were conducted over 2 yr (2019 to 2020) at two locations in Iowa to evaluate multi-tactic strategies for managing multiple herbicide–resistant (MHR) waterhemp [Amaranthus tuberculatus (Moq.) Sauer] in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. The effect of three herbicide programs on A. tuberculatus control was tested in corn (2019). The effects of the prior year’s corn weed control, a cereal rye (Secale cereale L.) cover crop, and soybean row spacing (38-cm vs. 76-cm wide) on A. tuberculatus density, biomass, and seed production were tested in soybean (2020). A herbicide program used in corn with two sites of action provided only 35% control of MHR A. tuberculatus compared with ≥97% control by a herbicide program with three sites of action. In soybean, adequate control of A. tuberculatus (≥90%) in the prior year’s corn crop and use of a cover crop or narrow rows reduced A. tuberculatus density by more than 60% at 3 and 9 wk after planting (WAP) compared with inadequate control (30%) in the prior year’s corn and no cover crop. Cover crop and narrow-row soybean reduced A. tuberculatus density by 44% at 3 WAP compared with no cover crop and wide-row soybean. Inclusion of a single control tactic, adequate control (≥90%) with multiple herbicides in the prior year’s corn, use of a cover crop, or narrow-row soybean reduced A. tuberculatus biomass and seed production at soybean harvest by at least 24% compared with inadequate control (30%) in the prior year’s corn, no cover crop, and wide-row soybean. The combination of all three control tactics reduced A. tuberculatus biomass and seed production at soybean harvest by at least 80%. In conclusion, diverse control tactics targeting A. tuberculatus at multiple life-cycle stages can make substantial contributions to the management of MHR populations.

Vipergrass [Dinebra retroflexa (Vahl) Panzer] is an annual weed of the Poaceae family distributed in several parts of Australia, Asia, and Europe. Very limited information is available on its germination response to different environmental conditions. Knowledge of its seed ecology and biology could help in formulating better weed management decisions. Experiments were conducted to study the effect of alternating temperatures, light conditions, salt stress, water stress, seed burial depths, and wheat residue amounts on the germination or emergence of D. retroflexa. Also, different pre- and postemergence herbicides were evaluated to control D. retroflexa. The highest germination (98%) was recorded at 30/20 C followed by 35/25 C (95%). Light was required for the germination of D. retroflexa. Germination decreased with an increase in sodium chloride (NaCl) concentrations. Even at 80 mM NaCl, 81% of seeds germinated, indicating D. retroflexa’s high salt tolerance. Seed germination gradually decreased with an increase in water stress, and no germination was recorded at −0.8 MPa osmotic potential. The emergence of D. retroflexa decreased with an increase in seed burial depths. The highest germination (83%) was recorded for surface-sown seeds, and emergence was reduced to 0 at a burial depth of 2 cm. Seedling emergence decreased from 82% to 2% when the crop residue load was increased from 0 to 800 kg ha−1. Applications of preemergence herbicides (at field rates), such as diuron, isoxaflutole, pendimethalin, pyroxasulfone, S-metolachlor, terbuthylazine, and triallate, and postemergence herbicides, such as clethodim, haloxyfop-methyl, glufosinate, glyphosate, imazamox plus imazapyr (a commercial mixture), and paraquat, resulted in complete control (100%) of D. retroflexa. Knowledge gained from this study will help us to understand the potential spread of D. retroflexa to other areas and to formulate integrated weed management strategies for its effective control.