Cotton producers need residual herbicides that can safely and practically be applied postemergence. Herbicide-coated fertilizers could allow for simultaneous application of residual herbicides and a bulk fertilizer blend. Therefore, a study was conducted in 2022 and 2023 in Fayetteville, AR, to evaluate cotton tolerance to 12 herbicide treatments coated onto a fertilizer blend and applied over cotton. Herbicides and rates evaluated included diuron at 840 g ai ha−1, florpyrauxifen-benzyl at 29 g ai ha−1, flumioxazin at 105 g ai ha−1, flumioxazin + pyroxasulfone at 70 + 90 g ai ha−1, fluridone at 168 g ai ha−1, fluometuron at 840 g ai ha−1, fomesafen at 280 g ai ha−1, pyroxasulfone at 128 g ai ha−1, saflufenacil at 66 g ai ha−1, saflufenacil + dimethenamid-P at 25 + 219 g ai ha−1, saflufenacil + pyroxasulfone at 44 + 91 g ai ha−1, and S-metolachlor at 1,388 g ai ha−1. In both years, fluridone, fluometuron, diuron, and S-metolachlor caused less than 10% injury at 7 d after treatment (DAT). Higher injury levels were observed in 2022 (19% to 30%) compared with 2023 (4% to 12%) for flumioxazin, fomesafen, saflufenacil, saflufenacil plus dimethenamid-P, and saflufenacil + pyroxasulfone. The elevated injury in one of two years was attributed to the presence of dew when the herbicide-coated fertilizer was applied. The initial injury was transient, as the cotton generally had recovered by 28 DAT for all herbicides. No differences in seed cotton yield or groundcover among the herbicide treatments occurred either year. These results highlight the potential of using several postemergence-applied, residual herbicides coated onto fertilizer that are not currently registered for over-the-top use in cotton.

Weeds belonging to the Amaranthus family are most problematic for soybean producers. With Palmer amaranth evolving resistance to multiple herbicides labeled for use in soybean, producers seek new sites of action to integrate into season-long herbicide programs. Bayer CropScience plans to launch a Convintro™ brand of herbicides, one being a premixture that will include diflufenican (categorized as a Group 12 herbicide by the Weed Science Society of America [WSSA]), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), for use preemergence in soybean. Research trials were conducted in Fayetteville and Keiser, AR, and Holt, MI, in 2022 and 2023, to evaluate the premixture in a season-long program in a dicamba-resistant soybean system. A 0.17:0.35:0.48 ratio of a premixture of diflufenican:metribuzin:flufenacet (DFF-containing premixture) was applied preemergence with different combinations of glyphosate, glufosinate, dicamba, and acetochlor at 28 (early postemergence) and 42 (late postermergence) days after planting (DAP). At the early postemergence timing, the DFF-containing premixture provided >90% control of Palmer amaranth and prickly sida. However, common ragweed, common lambsquarters, morningglory ssp., and annual grass control was ≤80% at this timing. When the late postemergence applications occurred, treatments that had already received an early postemergence application controlled prickly sida, morningglory ssp., Palmer amaranth, and annual grasses to a greater extent than those that had not, indicating the preemergence application of the DFF-containing premixture was not sufficient to provide control of the weed spectrum through 42 DAP. By 70 DAP, all programs provided ≥93% control of all weeds evaluated. Herbicide programs that included the DFF-containing premixture preemergence followed by (fb) EPOST fb LPOST common ragweed, common lambsquarters, morningglory ssp., and annual grasses to a greater than the one-pass postemergence systems. In addition, all herbicide programs evaluated in this study reduced Palmer amaranth seed production by >99%. However, producers who plan to use the DFF-containing premixture may need two postemergence herbicide applications to obtain high levels of weed control throughout the growing season.

With Palmer amaranth and waterhemp evolving resistance to nine and six different sites of action (SOAs) globally, soybean producers continue to search for new options to control these problematic weeds. Bayer CropScience has announced its intentions to launch a Convintro™ brand of herbicides, one being a three-way premixture for preemergence use in soybean. The premixture will contain diflufenican (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), adding a new SOA for soybean producers throughout the United States. With the anticipated launch of the premixture, research is needed to evaluate the length of residual control provided by the new herbicide. Research trials were conducted in Fayetteville and Keiser, AR, and Morrice, MI, in 2022 and 2023. A 0.17:0.35:0.48 ratio of a diflufenican:metribuzin:flufenacet (DFF)-containing premixture was applied alone and in combination with additional metribuzin and dicamba. Also, metribuzin, acetochlor, a S-metolachlor:metribuzin premixture, and a flumioxazin:pyroxasulfone:metribuzin premixture were applied preemergence. The DFF-containing premixture was more effective in reducing Palmer amaranth/waterhemp emergence than acetochlor in four of six trials at 28 d after treatment (DAT). Palmer amaranth and waterhemp densities in plots treated with the DFF-containing premixture exhibited similar results to plots treated with the S-metolachlor:metribuzin premixture and the flumioxazin:pyroxasulfone:metribuzin premixture at 28 DAT. By 56 DAT, Palmer amaranth and waterhemp densities were comparable or superior in plots with the DFF-containing premixture than in those treated with acetochlor and metribuzin, and the S-metolachlor:metribuzin premixture at five of six sites. The addition of dicamba or metribuzin to the DFF-containing premixture did not reduce Palmer amaranth or waterhemp density compared to the DFF-containing premixture at 28 or 56 DAT. Overall, the DFF-containing premixture generally provided greater or comparable control over several standard herbicides, providing growers a new product for preemergence control of Amaranthus species in soybean fields.

Bayer Crop Science anticipates launching several premixtures for use in soybean, targeted at control of Palmer amaranth. One of the premixtures will contain diflufenican (Weed Science Society of America [WSSA] Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15) (DFF-containing premixture), offering an alternative site of action for soybean producers. Field experiments were conducted in Arkansas and Michigan to evaluate application timings of the DFF-containing premixture for soybean tolerance and weed control and possible cultivar tolerance differences to diflufenican and the DFF-containing premixture. Soybean injury from the 1X and 2X rates of the DFF-containing premixture ranged from 0% to 60% 14 d after planting (DAP), with injury increasing the closer the herbicide was applied to soybean emergence. Excluding the 2X rate applied 3 DAP in Arkansas in 2023, soybean injury was <20% regardless of location, site-year, application timing, and rate. For weed control experiments, only a 1X rate of the DFF-containing premixture was applied at the various application timings. Control of five weed species, encompassing broadleafs and grasses, ranged from 81% to 98%, regardless of application timing, by 28 DAP. By 42 DAP, weed control ranged from 71% to 97%, with the 14-d preplant application timing typically being the least effective. The DFF-containing premixture and diflufenican alone were applied PRE at 1X and 2X rates for the soybean cultivar study. Soybean metribuzin sensitivity did not affect the degree of crop response, even in a high-pH soil, and injury to soybean never exceeded 20%. Overall, the DFF-containing premixture will be a tool that soybean producers can integrate into a season-long herbicide program for use across the United States regardless of soybean cultivar.

Investigations of the relevance of low-tunnel methodology and air sampling concerning the off-target movement of dicamba were conducted from 2018 to 2022, focused primarily on volatility. This research, divided into three experiments, evaluated the impact of herbicides and adjuvants added to dicamba and the type of surface treated on dicamba volatility. Treatment combinations included glyphosate and glufosinate, the presence of a simulated contamination rate of ammonium sulfate (AMS), the benefit of a volatility reduction agent (VRA), and a vegetated (dicamba-resistant cotton) or soil surface treated with dicamba. Volatility assessments included air sampling collected over 48 h. Dicamba treatments were applied four times to each of two bare soil or cotton trays and placed inside the tunnels. Dicamba from air samples was extracted and quantified. Field assessments included the maximum and average visible injury in bioindicator soybean and the lateral movement of dicamba damage expressed by the farthest distance from the center of the plots to the position in which plants exhibited 5% injury. Adding glufosinate and glyphosate to dicamba increased the dicamba amount in air samples. A simulated tank contamination rate of AMS (0.005% v/v) did not affect dicamba emissions compared to a treatment lacking AMS. Adding a VRA reduced dicamba in air samples by 70% compared to treatment without the adjuvant. Dicamba treatments applied on vegetation generally produced greater detectable amounts of dicamba than treatments applied to bare soil. Field assessment results usually followed differences in dicamba concentration by treatments tested. Results showed that low-tunnel methodology allowed simultaneous comparisons of several treatment combinations concerning dicamba volatility.

Emergency departments are high-risk settings for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) surface contamination. Environmental surface samples were obtained in rooms with patients suspected of having COVID-19 who did or did not undergo aerosol-generating procedures (AGPs). SARS-CoV-2 RNA surface contamination was most frequent in rooms occupied by coronavirus disease 2019 (COVID-19) patients who received no AGPs.

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 threat of herbicide-resistant weed species, such as Palmer amaranth, has driven the development of robust weed management programs that rely on more than chemicals for weed control. Previous research has shown that zero-tolerance weed thresholds, cover crops, deep tillage, and diverse herbicide programs are effective strategies for controlling Palmer amaranth. Unfortunately, research investigating the integration of all four of these weed management strategies in a system is lacking. To better leverage these integrated weed management strategies in cotton production systems, a long-term study was initiated in fall 2018 near Marianna, AR, with zero tolerance, deep tillage, a cereal rye cover crop, and either a dicamba or non-dicamba in-crop herbicide program as factors. Results found that total Palmer amaranth emergence was reduced 76% as the result of deep tillage in 2019 and, in the absence of a zero-tolerance strategy, 73% in 2020. In the absence of a zero-tolerance strategy, the combination of a non–cover crop strategy and dicamba herbicide program decreased total Palmer amaranth emergence by 73%, while the combination of a cover crop strategy and dicamba herbicide program decreased total Palmer amaranth emergence by 78% compared to the combination of a cover crop and non-dicamba herbicide program. Under a zero-tolerance strategy in 2019, tillage reduced cotton yield by 12% and partial returns by US$370 ha−1. In 2020, tillage reduced cotton yield by 14% and partial returns of US$371 ha−1 under a non-zero-tolerance strategy, while a 12% yield reduction and a US$260 ha−1 decrease in partial returns were observed under a zero-tolerance strategy. In 2019, the non-dicamba program resulted in greater partial returns than the dicamba in-crop program because of greater yield and lower program costs. However, in 2020, partial returns were greater for the dicamba in-crop herbicide program owing to greater yields achieved by this program.

The ability of weed populations to evolve resistance to herbicides affects management strategies and the profitability of crop production. The objective of this research was to screen Palmer amaranth accessions from Arkansas for glufosinate resistance. Additional efforts focused on the effectiveness of various herbicides, across multiple sites of action (SOAs), on each putative-resistant accession. The three putative accessions were selected from 60 Palmer amaranth accessions collected in 2019 and 2020 and screened with to 0.5× and 1× rates of glufosinate. A dose-response experiment was conducted for glufosinate on accessions A2019, A2020, and B2020. The effectiveness of various preemergence- and postemergence-applied herbicides were evaluated on each accession. Resistance ratios of A2019, A2020, and B2020 to glufosinate ranged from 5.1 to 27.4 when comparing LD50 values to two susceptible accessions, thus all three accessions were resistant to glufosinate. All three accessions (A2019, A2020, and B2020) were found to have a reduction equal to or greater than 20 percentage points in mortality to at least one herbicide from five different SOAs equal to or greater than five sites of action. Herbicides from nine different SOAs controlled A2019 at least 20 percentage points less than the susceptible accessions, which points to a need for additional research to characterize the response of this accession.

Background: Aerosol-generating procedures (AGPs) performed on COVID-19–positive patients raise concerns about the dissemination of SARS-CoV-2 via aerosols and droplets. Infectious aerosols and droplets generated by SARS-CoV-2–positive patient AGPs or through direct COVID-19 patient coughing or exhalation could potentially contaminate surfaces, leading to the indirect spread of SARS-CoV-2 via fomites within the emergency department (ED). We sampled surfaces of ED patient rooms occupied by known SARS-CoV-2–positive patients or patients under investigation for COVID-19 and undergoing an AGP to determine the frequency of room contamination with SARS-CoV-2 RNA. Methods: Swabs were collected from 5 room surfaces in the ED following AGPs performed on patients under investigation for COVID-19 or positive for SARS-CoV-2. High- and low-touch surfaces 6 feet (2 m) from the patient (door handle and return vent, respectively) and reusable medical equipment were swabbed. Swabs were tested for SARS-CoV-2 RNA by RT-qPCR; positive samples were cultured in Vero E6 cells. Patient COVID-19 results were confirmed through the electronic medical record. Results: In total, 203 rooms were sampled: 43 SARS-CoV-2–positive patients with an AGP, 44 SARS-CoV-2–positive patients who did not have an AGP, and 116 SARS-CoV-2–negative patients with an AGP, for a total of 1,015 swabs. Overall, SARS-CoV-2 RNA was detected on 36 (3.5%) surfaces from 29 rooms (14.3%) (Table 1). RNA contamination was detected more frequently in rooms occupied by SARS-CoV-2–positive patients who did not have an AGP than rooms occupied by COVID-19 patients (30% vs 14%). SARS-CoV-2 RNA was also detected in rooms occupied by SARS-CoV-2–negative patients undergoing an AGP (9%). SARS-CoV-2 RNA was most frequently detected on air vents (n = 15), bedrails (n = 10), equipment and vital signs monitors (n = 4 each), and door handles (n = 3). One bedrail was positive by culture and confirmed by an RT-qPCR cycle threshold reduction from >40 to 13. Conclusions: We detected SARS-CoV-2 RNA contamination on room surfaces in the ED, regardless of patient AGP or COVID-19 status; however, RNA contamination of room surfaces was most common in rooms occupied by SARS-CoV-2–positive patients who did not have an AGP, which may be attributable to stage of disease and viral shedding. SARS-CoV-2 RNA contamination was also present in rooms where APGs were performed on SARS-CoV-2–negative patients, suggesting carryover from previous patients. SARS-CoV-2 RNA was found most often on room air-return vents, further emphasizing the importance of aerosols in the spread of SARS-CoV-2.

Funding: None

Disclosures: None

Palmer amaranth has developed resistance to at least seven herbicide sites of action in the Cotton Belt of the United States, leaving producers with fewer options to manage this weed. Previous research with corn and newly commercially released soybean systems have found the use of 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides such as isoxaflutole (IFT) to be effective at managing Palmer amaranth. Consequently, a new transgenic cultivar of cotton is being developed with tolerance to IFT, allowing for in-crop applications of the herbicide. Two separate studies were conducted near Marianna, AR, in 2019 and replicated in 2020, to investigate the crop safety and utility of IFT when added to cotton herbicide programs. Herbicide programs featured IFT as a preemergence or early-postemergence option, residual herbicides in subsequent postemergence applications, and the presence or absence of a layby application. The use of IFT did not significantly impact cotton injury or yield, whereas the use of layered residual herbicides, including IFT, increased Palmer amaranth control compared to those without. Regardless of earlier use of IFT, layby applications were needed for season-long control of Palmer amaranth, entireleaf morningglory, broadleaf signalgrass, and johnsongrass, as evidenced by greater than a 20 percentage point improvement in control of all weeds when a layby application was made. Overall, findings from these studies indicate IFT to be a suitable tool for managing Palmer amaranth and will provide an additional site of action for cotton herbicide programs. Sequential herbicide applications and overlaying residuals were found to be paramount for managing Palmer amaranth throughout the season.

Dicamba residues in sprayers are difficult to remove and may interact with subsequent herbicides, including contact herbicides labeled for use in soybean. Without proper tank cleanout, applicators treating dicamba-resistant and non–dicamba resistant crops are at risk of contaminating the spray solution with dicamba residue from previous applications. Experiments were conducted in Fayetteville, AR, in 2018 and 2019, with the first experiment evaluating consequences of dicamba tank contamination with contact herbicides and the second experiment addressing the impact of dicamba exposure on a glufosinate-resistant soybean cultivar relative to a contact herbicide application. Experiments for tank contamination and timing of dicamba exposure were designed as a three-factor and a two-factor randomized complete block with four replications, respectively, considering site-year as a fixed effect in each experiment. Dicamba at 0, 0.056, 0.56, and 5.6 g ae ha−1 was applied alone, with glufosinate, with acifluorfen, or with glufosinate plus acifluorfen to V3 soybean. Dicamba applied in combination with contact herbicides exacerbated visible auxin symptomology over dicamba alone at 21 and 28 d after treatment (DAT), while dicamba at 5.6 g ae ha−1 reduced soybean height. Injury and height reductions caused by dicamba mixtures with contact herbicides did not reduce grain yield. In the second experiment, dicamba was applied at 2.8 g ae ha−1 at VC, V1, V2, and V3 and at 3, 7, and 10 d after a glufosinate application to V3 soybean (DATV3). Greater soybean injury was observed when dicamba exposure followed a glufosinate application than when dicamba preceded glufosinate or was applied in a mixture with glufosinate, with yield reductions resulting from 7 and 10 DATV3 dicamba applications. Dicamba exposure in the presence of contact herbicides resulted in increased auxin symptomology and can be intensified if soybean are exposed to dicamba following a contact herbicide application.

Previous research has shown that glufosinate and nicosulfuron at low rates can cause yield loss to grain sorghum. However, research has not been conducted to pinpoint the growth stage at which these herbicides are most injurious to grain sorghum. Therefore, field tests were conducted in 2016 and 2017 to determine the most sensitive growth stage for grain sorghum exposure to both glufosinate and nicosulfuron. Field test were designed with factor A being the herbicide applied (glufosinate or nicosulfuron). Factor B consisted of timing of herbicide application including V3, V8, flagleaf, heading, and soft dough stages. Factor C was glufosinate or nicosulfuron rate where a proportional rate of 656 g ai ha−1 of glufosinate and 35 g ai ha−1 of nicosulfuron was applied at 1/10×, 1/50×, and 1/250×. Visible injury, crop canopy heights (cm), and yield were reported as a percent of the nontreated. At the V3 growth stage visible injury of 32% from the 1/10× rate of glufosinate and 51% from the 1/10× rate of nicosulfuron was observed. This injury was reduced by 4 wk after application (WAA) and no yield loss occurred. Nicosulfuron was more injurious than glufosinate at a 1/10× and 1/50× rate when applied at the V8 and flagleaf growth stages resulting in death of the shoot, reduced heading, and yield. Yield losses from the 1/10× rate of nicosulfuron were observed from V8 through early heading and ranged from 41% to 96%. Yield losses from the 1/50× rate of nicosulfuron were 14% to 16% at the flagleaf and V8 growth stages respectively. The 1/10× rate of glufosinate caused 36% visible injury 2 WAA when applied at the flagleaf stage, which resulted in a 16% yield reduction. By 4 WAA visible injury from either herbicide at less than the 1/10× rate was not greater than 4%. Results indicate that injury can occur, but yield losses are more probable from low rates of nicosulfuron at V8 and flagleaf growth stages.

A non-GMO trait called Inzen™ was recently commercialized in grain sorghum to combat weedy grasses, allowing the use of nicosulfuron POST in the crop. Inzen™ grain sorghum carries a double mutation in the acetolactate synthase (ALS) gene Val560Ile and Trp574Leu, which potentially results in cross-resistance to a wide assortment of ALS-inhibiting herbicides. To evaluate the scope of cross-resistance to Weed Science Society of America Group 2 herbicides in addition to nicosulfuron, tests were conducted in 2016 and 2017 at the Lon Mann Cotton Research Station near Marianna, AR, the Arkansas Agricultural Research and Extension Center in Fayetteville, AR, and in 2016 at the Pine Tree Research Station near Colt, AR. The tests included ALS-inhibiting herbicides from all five families: sulfonylureas, imidazolinones, pyrimidinylthiobenzoics, triazolinones, and triazolopyrimidines. Treatments were made PRE or POST to grain sorghum at a 1× rate for crops in which each herbicide is labeled. Grain sorghum planted in the PRE trial were Inzen™ and a conventional cultivar. Visible estimates of injury and sorghum heights were recorded at 2 and 4 wk after herbicide application, and yield data were collected at crop maturity. In the PRE trial, no visible injury, sorghum height reduction, or yield loss were observed in plots containing the Inzen™ cultivar. Applications made POST to the Inzen™ grain sorghum caused visible injury, sorghum height reduction, and yield loss of 20%, 13%, and 35%, respectively, only in plots where bispyribac-Na was applied. There was no impact on the crop from other POST-applied ALS-inhibiting herbicides. These results demonstrate that the Inzen™ trait confers cross-resistance to most ALS-inhibiting herbicides and could offer promising new alternatives for weed control and protection from carryover of residual ALS-inhibiting herbicides in grain sorghum.

Atrazine offers growers a reliable option to control a broad spectrum of weeds in grain sorghum production systems when applied PRE or POST. However, because of the extensive use of atrazine in grain sorghum and corn, it has been found in groundwater in the United States. Given this issue, field experiments were conducted in 2017 and 2018 in Fayetteville and Marianna, Arkansas, to explore the tolerance of grain sorghum to applications of assorted photosystem II (PSII)-inhibiting herbicides in combination with S-metolachlor (PRE and POST) or mesotrione (POST only) as atrazine replacements. All experiments were designed as a factorial, randomized complete block; the two factors were (1) PSII herbicide and (2) the herbicide added to create the mixture. The PSII herbicides were prometryn, ametryn, simazine, fluometuron, metribuzin, linuron, diuron, atrazine, and propazine. The second factor consisted of either no additional herbicide, S-metolachlor, or mesotrione; however, mesotrione was excluded in the PRE experiments. Crop injury estimates, height, and yield data were collected or calculated in both studies. In the PRE study, injury was less than 10% for all treatments except those containing simazine, which caused 11% injury 28 d after application (DAA). Averaged over PSII herbicide, S-metolachlor–containing treatments caused 7% injury at 14 and 28 DAA. Grain sorghum in atrazine-containing treatments yielded 97% of the nontreated. Grain sorghum receiving other herbicide treatments had significant yield loss due to crop injury, compared with atrazine-containing treatments. In the POST study, ametryn- and prometryn-containing treatments were more injurious than all other treatments 14 DAA. Grain sorghum yield in all POST treatments was comparable to atrazine, except prometryn plus mesotrione, which was 65% of the nontreated. More herbicides should be evaluated to find a comparable fit to atrazine when applied PRE in grain sorghum. However, when applied POST, diuron, fluometuron, linuron, metribuzin, propazine, and simazine have some potential to replace atrazine in terms of crop tolerance and should be further tested as part of a weed control program across a greater range of environments.

Narrow-windrow burning has been a successful form of harvest weed seed control in Australian cropping systems, but little is known about the efficacy of narrow-windrow burning on weed seeds infesting U.S. cropping systems. An experiment was conducted using a high-fire kiln that exposed various grass and broadleaf weed seeds to temperatures of 200, 300, 400, 500, and 600 C for 20, 40, 60, and 80 s to determine the temperature and time needed to kill weed seeds. Weeds evaluated included Italian ryegrass, barnyardgrass, johnsongrass, sicklepod, Palmer amaranth, prickly sida, velvetleaf, pitted morningglory, and hemp sesbania. Two field experiments were also conducted over consecutive growing seasons, with the first experiment aimed at determining the amount of heat produced during burning of narrow windrows of soybean harvest residues (chaff and straw) and the effect of this heat on weed seed mortality. The second field experiment aimed to determine the effect of wind speed on the duration and intensity of burning narrow windrows of soybean harvest residues. Following exposure to the highest temperature and longest duration in the kiln, only sicklepod showed any survival (<1% average); however, in most cases, the seeds were completely destroyed (ash). A heat index of only 22,600 was needed to kill all seeds of Palmer amaranth, barnyardgrass, and Italian ryegrass. In the field, all seeds of the evaluated weed species were completely destroyed by narrow-windrow burning of 1.08 to 1.95 kg m−2 of soybean residues. The burn duration of the soybean harvest residues declined as wind speed increased. Findings from the kiln and field experiments show that complete kill is likely for weed seeds concentrated into narrow windrows of burned soybean residues. Given the low cost of implementation of narrow-windrow burning and the seed kill efficacy on various weed species, this strategy may be an attractive option for destroying weed seed.

Weed control in corn traditionally has relied on atrazine as a foundational tool to control problematic weeds. However, the recent discovery of atrazine in aquifers and other water sources increases the likelihood of more strict restrictions on its use. Field-based research trials to find atrazine alternatives were conducted in 2017 and 2018 in Fayetteville, AR, by testing the tolerance of corn to PRE and POST applications of different photosystem II (PSII) inhibitors alone or in combination with mesotrione or S-metolachlor. All experiments were designed as a two-factor factorial, randomized complete block, with the two factors being (1) PSII-inhibiting herbicide and (2) the herbicide added to create the mixture. The PSII-inhibiting herbicides were prometryn, ametryn, simazine, fluometuron, metribuzin, linuron, diuron, atrazine, and propazine. The second factor consisted of either no additional herbicide, S-metolachlor, or mesotrione. Treatments were applied immediately after planting in the PRE experiments and to 30-cm–tall corn for the POST experiments. For the PRE study, low levels of injury (<15%) were observed at 14 and 28 d after application and corn height was negatively affected by the PSII-inhibiting herbicide applied. PRE-applied fluometuron- and ametryn-containing treatments consistently caused injury to corn, often exceeding 5%. Because of low injury levels caused by all treatments, crop density and yield did not differ from that of the nontreated plants. For the POST study, crop injury, relative height, and relative yield were affected by PSII-inhibiting herbicide and the herbicide added. Ametryn-, diuron-, linuron-, propazine-, and prometryn-containing treatments caused at least 25% injury to corn in at least 1 site-year. All PSII-inhibiting herbicides, except metribuzin and simazine when applied alone, caused yield loss in corn when compared with atrazine alone. Diuron-, linuron-, metribuzin-, and simazine-containing treatments applied PRE and metribuzin- and simazine-containing treatments applied POST should be investigated further as atrazine replacements.

This paper presents a comprehensive investigation into flow past a circular cylinder where compressibility and rarefaction effects play an important role. The study focuses on steady subsonic flow in the Reynolds-number range 0.1–45. Rarefaction, or non-equilibrium, effects in the slip and early transition regime are accounted for using the method of moments and results are compared to data from kinetic theory obtained from the direct simulation Monte Carlo method. Solutions obtained for incompressible continuum flow serve as a baseline to examine non-equilibrium effects on the flow features. For creeping flow, where the Reynolds number is less than unity, the drag coefficient predicted by the moment equations is in good agreement with kinetic theory for Knudsen numbers less than one. When flow separation occurs, we show that the effects of rarefaction and velocity slip delay flow separation and will reduce the size of the vortices downstream of the cylinder. When the Knudsen number is above 0.028, the vortex length shows an initial increase with the Reynolds number, as observed in the standard no-slip continuum regime. However, once the Reynolds number exceeds a critical value, the size of the downstream vortices decreases with increasing Reynolds number until they disappear. An existence criterion, which identifies the limits for the presence of the vortices, is proposed. The flow physics around the cylinder is further analysed in terms of velocity slip, pressure and skin friction coefficients, which highlights that viscous, rarefaction and compressibility effects all play a complex role. We also show that the local Knudsen number, which indicates the state of the gas around the cylinder, can differ significantly from its free-stream value and it is essential that computational studies of subsonic gas flows in the slip and early transition regime are able to account for these strong non-equilibrium effects.