Corn Herbicides Research Articles

Using Cover Crops as Means of Controlling Weeds and Reducing the Applied Quantity of Glyphosate-Based Herbicide in No-Till Glyphosate Tolerant Soybean and Corn

Weeds represent a serious drawback affecting the productivity of field crops worldwide. While the most common approach to control weeds in no-till practices is the use of glyphosate-based herbicides (GBHs), reducing their use represents a major challenge. This two-year field study aims to evaluate whether the use of cover crops (CC) in transgenic soybean and corn productions can (1) help control weeds and (2) reduce the amount of GBH needed for managing weeds. Sampling was carried out in 32 experimental field plots (four crop managements with four replicates on both crops). Crop managements consisted of GBH applications at rates of 0.84, 1.67, and 3.3 L ha−1 in plots in direct seeding with CC (DSCC) and at rates of 3.3 L ha−1 in plots without CC (DS). Weed cover rates, plant parameters (fresh and dry weights and heights), grain yields, water, and cation contents in soil were considered as indicators of interspecific competition. Results obtained in both years show that it is possible to reduce GBH use by 50% in plots with CC compared to plots without CC using a rate of GBH application of 3.33 L ha−1 (DS 3.3). However, weeds had a large impact on water content in soil, which was reflected by smaller plants and lower yields in plots with only 0.84 L ha−1 of GBH applied. In the context of the study, the use of CCs seems to facilitate the development of more sustainable agriculture while reducing the quantities of GBH generally used.

Very long chain fatty acid–inhibiting herbicides: Current uses, site of action, herbicide-resistant weeds, and future

Abstract The herbicides that inhibit very-long-chain fatty acid (VLCFA) elongases are primarily used for residual weed control in corn, barley, oat, sorghum, soybean, sugarcane, certain vegetable crops, and wheat production fields in the United States. They act primarily by inhibiting shoot development of susceptible species, preventing weed emergence and growth. The objectives of this review were to summarize 1) the chemical family of VLCFA-inhibiting herbicides and their use in the United States, 2) the VLCFA biosynthesis in plants and their site of action, 3) VLCFA-inhibitor resistant weeds and their mechanism of resistance, and 4) the future of VLCFA-inhibiting herbicides. After their reclassification as Group 15 herbicides to include shoot growth-inhibiting herbicides (Group 8), the VLCFA-inhibiting herbicides are currently represented by eight chemical families (benzofurans, thiocarbamates, α-chloroacetamides, α-oxyacetamides, azolyl-carboxamides, isoxazolines, α-thioacetamides, and oxiranes). On average, VLCFA-inhibiting herbicides are applied once a year to both corn and soybean crops in the United States with acetochlor and S-metolachlor being the most used VLCFA-inhibiting herbicides in corn and soybean production, respectively. The site of action of Group 15 herbicides results from inhibition of the VLCFA synthase, which is encoded by several fatty acid elongase (FAE1)-like genes in VLCFA elongase complex in an endoplasmic reticulum. The VLCFA synthase is a condensing enzyme, and relies on a conserved, reactive cysteinyl sulfur in its active site that performs a nucleophilic attack on either the natural substrate (fatty acyl-CoA) or the herbicide. As of August 2023, 13 weed species have been documented to be resistant to VLCFA inhibitors, including 11 monocot weeds and two dicot weeds (Palmer amaranth and waterhemp). The isoxazolines (pyroxasulfone and fenoxasulfone) are the most recently (2014) discovered VLCFA-inhibiting herbicides. Although the intensity of VLCFA-inhibitor-directed discovery efforts has decreased over the past decade, this biochemical pathway remains a viable mechanistic target for the discovery of herbicide premixes and a valuable component of them.

First report of severe tolpyralate sensitivity in corn (Zea mays) discovers a novel genetic factor conferring crop response to a herbicide.

Tolpyralate, a relatively new inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), is registered for postemergence use in all types of corn (Zea mays L.) and has a record of excellent crop tolerance. A report of severe crop injury to sweet corn inbred (XSEN187) led to the following objectives: (i) determine whether sensitivity to tolpyralate in XSEN187 exists, and if confirmed, (ii) determine the genetic basis of tolpyralate sensitivity, and (iii) screen other corn germplasm for sensitivity to tolpyralate. Inbred XSEN187 was confirmed sensitive to tolpyralate. Inclusion of methylated seed oil or nonionic surfactant in the spray volume was necessary for severe crop injury. Tolpyralate sensitivity in XSEN187 is not conferred by alleles at Nsf1, a cytochrome P450-encoding gene (CYP81A9) conferring tolerance to many corn herbicides. Evidence suggests that tolpyralate sensitivity in XSEN187 is conferred by a single gene mapped to the Chr05: 283 240-1 222 909 bp interval. Moreover, tolpyralate sensitivity was observed in 48 other sweet corn and field corn inbreds. Severe sensitivity to tolpyralate exists in sweet corn and field corn germplasm when the herbicide is applied according to label directions. Whereas the corn response to several other herbicides, including HPPD-inhibitors, is conferred by the Nsf1 locus, corn sensitivity to tolpyralate is the result of a different locus. The use of tolpyralate should consider herbicide tolerance in inbred lines from which corn hybrids were derived, whereas alleles that render corn germplasm sensitive to tolpyralate should be eliminated from breeding populations, inbreds, and commercial cultivars. © 2023 Illinois Foundation Seeds, Inc and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Residual herbicides in corn and their effect on fall‐planted cover crop species

AbstractThe use of residual herbicides as a part of preemergence (PRE) and in‐season layered treatments has proven to be an effective strategy for controlling late‐emerging broadleaf weed species in annual crops. However, the use of residual PRE herbicides has the potential to negatively affect other crops within an annual two‐crop rotation, such as fall‐planted cover crops. The intent of this study was to determine if PRE herbicides commonly used in the upper Midwest United States would affect stand density, height, and biomass production of fall‐planted cover crops. Field studies were conducted at three locations that differed in soil type and climate. Four PRE herbicides were applied in silage corn (Zea mays L.) in the spring: dimethenamid‐P (single application), dimethenamid‐P + saflufenacil, acetochlor + clopyralid + mesotrione, and a layered treatment of dimethenamid‐P at planting and 30 days after first application. Three cover crops were planted in the fall following silage corn harvest with a no‐till drill: winter cereal rye (Secale cereale L.), winter camelina (Camelina sativa L.), and red clover (Trifolium pratense L.). Although some of the PRE HBs tested affected cover crop spring plant density and height in sandy soils, there was no difference in cover crop biomass production at termination between herbicide treatments, regardless of soil type. These results indicate that the application of these residual PRE herbicides for control of late‐emerging weed species did not interfere with cover crop biomass production as long as soil moisture was not limiting.

A follow‐up survey to assess stakeholders’ perspectives on weed management challenges and current practices in Nebraska, USA

AbstractStakeholders across the state of Nebraska, USA, were surveyed in 2019–2020 to assess problem weeds and weed management practices in agronomic crops. A total of 420 complete responses were obtained across four Nebraska districts (Northeast, Panhandle, Southeast, and West Central). Accumulated across the state, 65.5% of farmed or scouted crop ground in Nebraska was under no‐till production, with the major crops being corn and soybean representing 39.3% and 30.7% of agronomic crop production area, respectively. Palmer amaranth, horseweed, waterhemp, kochia, and giant ragweed were ranked the most problematic weeds. In a 2014–2015 survey, Palmer amaranth was the sixth most problematic weed. The most used preplant herbicides were 2,4‐D, glyphosate, and dicamba in the 2019–2020 survey. Atrazine applied alone or in mixture with acetochlor, bicyclopyrone, clopyralid, mesotrione, or S‐metolachlor were the most applied pre‐emergence (PRE) herbicides in corn, whereas the most applied PRE herbicides in soybean were metribuzin/sulfentrazone, flumioxazin/pyroxasulfone, and chloransulam‐methyl/sulfentrazone. Like the previous survey, glyphosate was the most frequent choice of survey respondents as a post‐emergence (POST) herbicide in glyphosate‐resistant corn and soybean, while 2,4‐D was the most applied POST herbicide in grain sorghum and wheat. Most of the respondents (77%) were aware of the new multiple herbicide‐resistant crops, and 86% listed physical drift and volatility of dicamba/2,4‐D as a primary concern. Twenty‐three percent of survey respondents identified integrated pest management as a primary research and extension priority for profitable agronomic crop production in Nebraska.

Preemergence herbicide premixes reduce the risk of soil residual weed control failure in corn

AbstractWidespread occurrence of herbicide-resistant weeds and more variable weather conditions across the United States has made weed control in many crops more challenging. Preemergence (PRE) herbicides with soil residual activity have resurged as the foundation for early season weed control in many crops. Field experiments were conducted in Janesville and Lancaster, Wisconsin, in 2021 and 2022 (4 site-years) to evaluate the weed control efficacy of solo (single site of action [SOA]) and premix (two or more SOAs) PRE herbicides in conventional tillage corn. Treatments consisted of 18 PRE herbicides plus a nontreated check. At the Janesville-2021 site, S-metolachlor + bicyclopyrone + mesotrione, atrazine + S-metolachlor + bicyclopyrone + mesotrione, and clopyralid + acetochlor + mesotrione provided >72% giant ragweed control. At the Janesville-2022 site, none of the PRE herbicides evaluated provided >70% giant ragweed control due to the high giant ragweed density and the lack of timely rainfall. At the Lancaster-2021 site, atrazine, dicamba, and flumetsulam + clopyralid provided <45% waterhemp control, but the remaining treatments provided >90% control. At the Lancaster-2022 site, the efficacy of some PRE herbicides was reduced due to the high waterhemp density; however, most herbicides provided >75% control. At the Lancaster-2021 and Lancaster-2022 sites, only dicamba and S-metolachlor did not provide >75% common lambsquarters control. Group 15 PRE herbicides provided >75% control of giant foxtail. Across weed species, PRE herbicides with two (78%) and three (81%) SOAs provided greater weed control than PRE herbicides with a single SOA (68%), indicating that at least two SOA herbicides applied PRE result in better early season weed control. The efficacy of the PRE herbicide treatments evaluated herein varied according to the soil seedbank weed community composition and environmental conditions (i.e., rainfall following application), but the premixes were a more reliable option to improve early season weed control in conventional tillage corn.

Using soybean chaff lining to manage waterhemp (Amaranthus tuberculatus) in a soybean–corn rotation

AbstractWaterhemp (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 maysL.) rotation in 2020 and 2021 in Ames, IA, and Roland, IA, to quantify the effectiveness of chaff lining for managingA. tuberculatusseeds. About 70% of theA. tuberculatusseeds were retained on the mother plant at soybean harvest in 2020. The chaff lining system concentrated more than 99% of theA. tuberculatusseeds exiting the combine into the chaff line. AlthoughA. tuberculatuspopulation density in 2021 was 76% higher inside the chaff line than outside the chaff line,A. tuberculatusaboveground biomass was 63% lower inside the chaff line than outside the chaff line at 12 wk after corn planting. Similarly,A. tuberculatusinside the chaff line had delayed emergence compared withA. tuberculatusoutside the chaff line. Application of preemergence herbicides in corn inside the chaff line delayedA. tuberculatusemergence by more than 2 wk compared withA. tuberculatusoutside the chaff line. Additionally, a follow-up postemergence herbicide application in corn was needed only inside the chaff line to manageA. 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 HRA. tuberculatusseedbanks.

Mutations in the acetolactate synthase (ALS) enzyme affect shattercane (Sorghum bicolor) response to ALS-inhibiting herbicides

BackgroundShattercane [Sorghum bicolor (L.) Moench ssp. Arundinaceum (Desv.)] is a competitive weed in North America's corn, soybean, sorghum, and other agronomic crops. Control of shattercane with POST herbicides in corn became possible with the introduction of acetolactate synthase (ALS)-inhibiting herbicides in the 1980s, and their extensive use resulted in the evolution of ALS-inhibitors resistant shattercane.ResultsShattercane seeds were collected from 16 south-eastern and south-central Nebraska fields that were treated with primisulfuron for three consecutive years. Three resistant plants were found in greenhouse evaluations of more than 30,000 plants. Results from a greenhouse bioassay conducted to assess the response of each shattercane biotype to ALS-inhibiting herbicides showed a differential response to ALS inhibitors within and between chemical classes. Biotype P8-30 was resistant or partially resistant to all ALS-inhibiting herbicides applied and displayed a unique amino acid sequence substitution (Trp574 to Leu) relative to the other two resistant biotypes, P2-205 and P9-102. Whole plant dose–response studies confirmed a 4- to the 12-fold level of primisulfuron resistance in three shattercane biotypes compared with the known primisulfuron-susceptible shattercane biotype. The ALS gene was sequenced using primers designed from the corn ALS sequence to identify mutations in the ALS gene that confer resistance. A total of seven nucleotide substitutions were detected in the three herbicide-resistant biotypes P2-205, P8-30, and P9-102. These biotypes are being crossed to adapted sorghum lines (grain, sweet, and forage) to broaden germplasm with resistance to ALS-inhibiting herbicides.ConclusionThe discovery of these mutants should accelerate the development of sorghum genotypes that tolerate ALS-based herbicides, which provide additional choices for sorghum farmers to control weeds, especially grasses, in their fields.

Continuous process for preparation of 2,3-dimethyl-4-methylsulfonylbromobenzene via oxidation by in situ formed peracetic acid

2,3-dimethyl-4-methylsulfonylbromobenzene(BDSO) is an important intermediate of topramezone, a highly effective corn herbicide. However, its synthesis requires peroxyacetic acid as oxidant and poses a safety risk. In this work, a continuous flow to in situ generations of peroxyacetic acid and thioether oxidation for the preparation of BDSO was developed using a three-stream micromixing process. By in-situ generation and consumption of peroxyacetic acid, the safety hazard of peroxyacetic acid was eliminated, and a green and efficient preparation of BDSO was also achieved. Compared to the batch reactor, the three-stream micromixing process has a shorter residence time(6 min), and higher space-time yield(8.56 mol L−1 h−1). This method has great potential in industrial applications.

The Discovery of Bicyclopyrone

Two short topics were presented in the lecture titled Some Highlights of an Agro Career presented at the Fall Meeting Swiss Chemical Society, September 10th, 2021. The first of these topics discussed the discovery of the selective corn herbicide Bicyclopyrone. The second topic presented was concerned with host marking pheromones (HMPs), and described the HMP of the Mexican fruit fly anastrepha ludens, and its use in crop protection. The story concerning the host marking pheromones of the Mexican fruit fly has already been published in this journal[1] and thus this review will describe the discovery of Bicyclopyrone.

Preparation of porous carbon-based molecularly imprinted polymers for separation of triazine herbicides in corn.

A synthesis route of using cellulose as the precursor to prepare porous carbon (PC) had been established in this study. The as-prepared PC was introduced as carriers in the synthesis process of porous carbon-molecularly imprinted polymers (PC-MIPs), which greatly improved the absorption capacity of MIPs. Triazine pesticides in corn were extracted with matrix solid-phase dispersion (MSPD) using the PC-MIPs as dispersants and determined by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Under the optimal MSPD condition for extracting six kinds of triazines (simazine, terbutryn, simetryne, prometryne, ametryn, and atrazine), the detection limits were 0.005-0.02ngg-1, while the precisions were 1.2-5.9%, and the recoveries were 92.6-104.7%. Themethod hasbeen extensively applied to analyze various corn samples. Atrazine residue (1.2μgkg-1) was detected in one corn sample, which was lower than the maximum residual limit indicated by the Chinese stated standards (50μgkg-1).

Future efficacy of pre-emergence herbicides in corn (Zea mays) is threatened by more variable weather.

BACKGROUNDBy 2050, weather is expected to become more variable with a shift towards higher temperatures and more erratic rainfall throughout the U.S. Corn Belt. The effects of this predicted weather change on pre‐emergence (PRE) herbicide efficacy have been inadequately explored. Using an extensive database, spanning 252 unique weather environments, the efficacy of atrazine, acetochlor, S‐metolachlor, and mesotrione, applied PRE alone and in combinations, was modeled on common weed species in corn (Zea mays L.).RESULTSAdequate rainfall to dissolve the herbicide into soil water solution so that it could be absorbed by developing weed seedlings within the first 15 days after PRE application was essential for effective weed control. Across three annual weed species, the probability of effective control increased as rainfall increased and was maximized when rainfall was 10 cm or more. When rainfall was less than 10 cm, increasing soil temperatures had either a positive or negative effect on the probability of effective control, depending on the herbicide(s) and weed species. Herbicide combinations required less rainfall to maximize the probability of effective control and had higher odds of successfully controlling weeds compared with the herbicides applied individually.CONCLUSIONSResults of this study highlight the importance of rainfall following PRE herbicide application. As rainfall becomes more variable in future, the efficacy of common PRE herbicides will likely decline. However, utilizing combinations of PRE herbicides along with additional cultural, mechanical, biological, and chemical weed control methods will create a more sustainable integrated weed management system and help U.S. corn production adapt to more extreme weather.© 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Discovery and structure optimization of a novel corn herbicide, tolpyralate.

Tolpyralate, a new selective postemergence herbicide developed for the weed control in corn, possesses a unique chemical structure with a 1-alkoxyethyl methyl carbonate group on the N-ethyl pyrazole moiety. This compound shows high herbicidal activity against many weed species, including glyphosate-resistant Amaranthus tuberculatus. Tolpyralate targets 4-hydroxyphenylpyruvate dioxygenase (4-HPPD), which is involved in the tyrosine degradation pathway. Inhibition of the enzyme destroys the chlorophyll, thereby killing the susceptible weeds. Details of tolpyralate discovery, structure optimization, and biological activities are described.

Evaluation of corn herbicide programs with and without atrazine

AbstractAtrazine is a foundational herbicide in corn (Zea mays L.) because of its broad‐spectrum weed control and utility for pre‐emergence or postemergence applications. Extensive atrazine use has led to traces in groundwater, surface water, and aquifers. This research explored corn herbicide regimes with little or no atrazine. Pre‐emergence herbicide treatments [S‐metolachlor (0.955 lb acre–1); saflufenacil (0.054 oz acre–1) plus dimethenamid‐P (0.473 lb acre–1)] and postemergence herbicide mixtures [bicyclopyrone (0.040 lb acre–1) plus mesotrione (0.161 lb acre–1) plus S‐metolachlor (1.429 lb acre–1); thiencarbazone‐methyl (0.013 lb acre–1) plus tembotrione (0.067 lb acre–1), thiencarbazone‐methyl (0.033 lb acre–1) plus isoxaflutole (0.082 lb acre–1); acetochlor (0.964 lb acre–1) plus mesotrione (0.103 lb acre–1) plus clopyralid (0.065 lb acre–1)] were applied alone or combined with atrazine at 0.50 lb acre–1 to glyphosate‐ or glufosinate‐resistant corn. All postemergence applications contained glyphosate (1.125 lb acre–1) plus glufosinate (0.402 lb acre–1). Palmer amaranth [Amaranthus palmeri (S.) Watson], broadleaf signalgrass [Urochloa platyphylla (Munro ex C. Wright) Nash], and pitted morningglory (Ipomoea lacunosa L.) control were always greater than 95%. Saflufenacil plus dimethenamid‐P injured corn 8 and 5% more than S‐metolachlor 21 d after pre‐emergence application. Averaged over pre‐emergence herbicide and atrazine rate, thiencarbazone‐methyl plus isoxaflutole injured corn by 21% in 2017. The addition of atrazine did not improve corn yield in 7 of 16 instances. According to this research, the weeds assessed at these densities can be controlled without atrazine by some programs.

Soil chemical properties as influenced by pre and post emergence herbicide in sweet corn grown in Vertisols

Field experiment was conducted at Department of Agronomy, College of Agriculture, Dhule during Kharif 2019 to study the effect of pre and post emergence herbicides on soil chemical properties in sweet corn. The treatment of weedy check (T1) recorded significantly higher soil organic carbon of 5.51 g kg-1. There was no variation in the soil organic carbon content among the treatments of pre and post emergence application of herbicides. The soil organic carbon in all these treatments of pre and post emergence application of herbicides was in the range of 5.43 to 5.45 g kg-1. The periodical soil available N was significantly influenced at 7, 15, 21, 30 and 45 days after application due to application of pre and post emergence herbicides to sweet corn. At harvest of sweet corn, the application of halosulfuron-methyl @ 90 g ha-1 as post emergence recorded significantly higher soil available N (208 kg ha-1), available P (17.11 kg ha-1) and available K (333.33 kg ha-1). The treatment of weedy check (T1) recorded significantly lower soil available N (195.33 kg ha-1), available P (15.33 kg ha-1) and available K (306.44 kg ha-1).

Pre‐emergence herbicides, not carrier volume, impacted weed management in conventional tillage systems

AbstractThe use of pre‐emergence (PRE) herbicides is resurging as a standard practice for weed management in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in the U.S. north‐central region. The increased use of PRE herbicides warrants investigation on the impact of spray carrier volume on weed control. Field experiments were established at Arlington, WI, in 2018 and 2019 and Janesville, WI, in 2018 to evaluate the influence of carrier volume on weed control of PRE herbicides in conventional tilled corn and soybean. Each experiment included three PRE herbicide premixes applied at crop planting at five carrier volumes (2.5, 5, 10, 15, and 17.5 gal acre−1). A nontreated control was also included in the experiment. Carrier volume did not influence weed control but PRE herbicide selection did. In corn, acetochlor + clopyralid + mesotrione and bicyclopyrone + mesotrione + S‐metolachlor provided 10–13% better annual grass, common ragweed (Ambrosia artemisiifolia L.), and giant ragweed (A. trifida L.) control than fluthiacet‐methyl + pyroxasulfone. In soybean, dimethenamid‐P + saflufenacil resulted in similar common ragweed control as the flumioxazin + pyroxasulfone treatment (79–85%), and 6 and 14% higher annual grass control and biomass reduction, respectively, compared to metribuzin + chlorimuron‐ethyl at Arlington. At Janesville, due to the high giant ragweed density in soybean, all herbicide treatments provided low levels of giant ragweed control (48–56%). Results from these field experiments suggest that lower carrier volumes could be used for PRE herbicide applications without compromising weed control in conventional tillage systems.

Biologically-Effective-Dose of Tolpyralate and Tolpyralate plus Atrazine for Control of Multiple-Herbicide-Resistant Waterhemp [<i>Amaranthus tuberculatus</i> (Moq.) J. D. Sauer] in Corn

The biologically-effective-dose of tolpyralate, a new 4-hydroxyphenyl-pyruvate dioxygenase (HPPD)-inhibitor, applied alone or tank-mixed with atrazine, for the control of multiple-herbicide-resistant (MHR) waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] has not been studied in corn. Seven field experiments were conducted during a three-year period (2018, 2019, 2020) in Ontario, Canada with MHR waterhemp to determine: 1) the dose-response of MHR waterhemp to tolpyralate and tolpyralate plus atrazine, and 2) the relative efficacy of tolpyralate and tolpyralate plus atrazine to post-emergence corn herbicides, dicamba/atrazine (500/1000 g·ha−1) and mesotrione + atrazine (100 + 280 g·ha−1). Tolpyralate + atrazine (120 + 4000 g·ha−1) caused 13% corn injury at one site two weeks after application (WAA), which was observed as transient foliar chlorosis and bleaching of new leaves. At 12 WAA, the predicted dose of tolpyralate for 50% control of MHR waterhemp at Cottam and on Walpole Island was 8 and 2 g·ha−1, respectively; the predicted dose of tolpyralate + atrazine for 50% control of MHR waterhemp at Cottam and on Walpole Island was 5 + 160 and 1 + 21 g·ha−1, respectively. The difference in predicted dose at the two sites is likely due to differences in MHR density and resistance profile. Applied at the registered rate, tolpyralate (30 g·ha−1) and tolpyralate + atrazine (30 + 1000 g·ha−1) controlled MHR waterhemp similar to dicamba/atrazine and mesotrione + atrazine across sites. This study demonstrates that tolpyralate + atrazine, applied POST, provides season-long control of MHR waterhemp in corn.

The effectiveness of applying herbicides incorn growing technology

Studies conducted on the chernozems of the steppe zone of Ukraine have revealed a direct relationship between thephytosanitary condition of an agricultural ecosystem and the amount of productive moisture used by corn plants from the 0 to 150 cmsoil layer during the period from sowing to harvest. In absolutely cleancrops, corn plants used soil water to the 156 mm depth, while in the plotsfrom which the weeds were not removedsoil water was used to 203 mm and on theherbicide-treated soilto 168–171 mm depth. Full or partial control of weediness of crops makes it possible to save 320–470 m3/ha moisture reserves, which is equal to the average monthly precipitation that fell during the growing season (2018–2019). Effectiveness of the tested crop chemical protection systems was to a large extend determined by the hydrothermal conditions in April - May. High air temperature, lack of agronomically useful rains and dry winds caused drying out of the upper soil layer and decreasedphytotoxicity of pre-emergence herbicides. In this case (2018), the largest percentage of the first wave weeds (89.1 %) was destroyed by a tank mixture of crop protectionagents contained in Frontier Optima (0.8 l/ha + Stellar (0.8 l/ha) + Metolat (0.8 l/ha). In favorable weather, to ensure manifestation of toxicological properties of soil herbicides (2019), the following combined technological schemes for harmful species control in the first stages of corn organogenesis had an advantage: Dual Gold (1.5 l/ha) (before sowing), Stellar (1.25 l/ha) + Metolat (1.25 l/ha) (after emergence of seedlings) and Acris(3 l/ha) (before sowing), Kelvin Plus (0.35 kg/ha) + Hasten (1 l/ha) (after emergence of seedlings). The technical efficiency of the herbicide application reached 98–100 %. In 2018, the highest yield of corn grain (7.85 t/ha) in the protected plots was obtained after application (in the phase of development of 3–5 corn leaves) of the following tank mixture: Frontier Optima (0.8 l/ha) + Stellar (0.8 l/ha) + Metolat (0.8 l/ha). This combination turned out to be the most effective in terms of cost effectiveness of grain production, providing a profitability of 213 %. In 2019, we managed to increase the yields by combining soil and crop protection herbicides. Given the cost and consumption rate of the herbicides used per 1 ha, a combination of synthetic agrochemicals Avatar (2.5 l/ha) (before sowing) + Prima (0.5 l/ha) (after emergence of seedlings) was the best in terms of the main product cost (1579 UAH/t) and profitability (134 %). Key words: weeds, herbicidal system, technical efficiency, productivity, profitability of production.

Annual ryegrass control prior to seeding corn with glyphosate plus group 2 herbicides

AbstractControl of fall‐seeded annual ryegrass (Lolium multiflorum Lam) cover crops with spring‐applied herbicides prior to seeding corn (Zea mays L.) has been variable. Improved herbicide options are needed in order to increase the consistency of annual ryegrass termination prior to seeding corn. Four field experiments were conducted over a 2‐yr period (2018, 2019) in Ontario, Canada, to evaluate the control of fall‐seeded annual ryegrass cover crops with various corn herbicides, applied prior to seeding corn in the spring. Based on visual estimates, glyphosate alone controlled annual ryegrass 80% at 6 weeks after application (WAA). Acetolactate synthase (ALS) inhibitor herbicides, foramsulfuron, nicosulfuron, rimsulfuron, and nicosulfuron/rimsulfuron controlled annual ryegrass 82, 71, 88, and 88%, respectively, at 6 WAA. The tankmix of glyphosate with foramsulfuron, nicosulfuron, rimsulfuron, or nicosulfuron/rimsulfuron controlled annual ryegrass 94–98% at 6 WAA. Glyphosate reduced annual ryegrass density 73%; in contrast, foramsulfuron, nicosulfuron, rimsulfuron, and nicosulfuron/rimsulfuron did not reduce annual ryegrass density compared to the weedy control. The tankmix of glyphosate plus an ALS inhibitor herbicide reduced annual ryegrass density 88−94%. Reduced annual ryegrass interference with glyphosate applied alone resulted in an increase in corn yield of 86% compared to the control. Reduced annual ryegrass interference with foramsulfuron, nicosulfuron, rimsulfuron, and nicosulfuron/rimsulfuron applied alone resulted in an increase in corn yield 61, 61, 93, and 91%, and 98, 105, 95, and 98% when co‐applied with glyphosate, respectively. The tankmix of glyphosate with an ALS inhibitor herbicide resulted in excellent (>90%) annual ryegrass control and increased corn yield.

Microwave absorption medium-assisted extraction coupled with reversed-phase dispersive liquid-liquid microextraction of triazine herbicides in corn and soybean samples.

A new extraction method, microwave absorption medium-assisted extraction coupled with reversed-phase dispersive liquid-liquid microextraction, was developed for the determination of triazine herbicides in corn and soybean samples. Triazine herbicides were extracted with hexane and then directly enriched into the ionic liquid phase. The purification of sample and concentration of target analytes were performed simultaneously. The method combines the advantages of nonpolar solvent dynamic microwave extraction and reversed-phase dispersive liquid-liquid microextraction, which could greatly simplify the operation and reduce the whole pretreatment time. The Box-Behnken design was used to the optimization of experimental factors involved in the dynamic microwave-assisted extraction. In the present study, good linearity in the range of 5.00-500.00µg/kg was obtained. The limits of detection and quantification varying from 1.3 to 4.2 and 4.1 to 13.9µg/kg were achieved, respectively. The intra- and interday precisions were between 2.7 and 6.9%. The present method was applied to the analysis of corn and soybean samples, and the recoveries of analytes ranged from 80.7 to 106.9% with the relative standard deviations of 2.1-7.8%. The present method shows the potentials of practical applications in the treatment of the complex fatty solid samples.